CA1178678A - Bidirectional, interactive fire detection system - Google Patents

Abstract

BIDIRECTIONAL, INTERACTIVE FIRE DETECTION SYSTEM

Abstract of the Disclosure A communication system useful for fire detection which transfers data/commands bi-directionally between a controller and connected transponders on a real time, interactive basis.
This system makes possible accurate data recovery, whether a transponder has its output shorted, or although multiple transponders are replying at the same time. The system makes possible the remote determination and constant monitoring of transducer sensitivity, at the controller. The sensitivity can be adjusted remotely at the controller, and different transducers can have different thresholds simultaneously.
These thresholds (limits) can be changed collectively or individually to different settings manually or automatically at the controller. The system trans-mits reference data for supervision of system ac-curacy. Compensation for long-term changes is provided for both transponders and transducers in this system.

Description

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BIDIRECTIONAL, INTERACTIVE FIRE DETECTION SYSTEM

Background of the Invention Various detectors and systems have been de~ieloped ~o detect and indicate the presence of particles of combustion, or of a fire, or of an increase in temperature. Such systems generally use two or more conductors between a control panel or control unit, which is coupled to the individual detectors. In general, the individual detectors determine when an undesired condition is present, by comparing some parameter (such as current flow or voltage level) with a predetermined reference value. When the detector determines the reference value has been exceeded, the undesired condition is present and the detector latches in the alarm condition. Generally the control unit does not know the precise location of the alarmed detector, and a ter three or more detectors have gone into alarm on one zone, cannot recognize how many detectors are in the alarmed condition on that zone~
Prior art detectors generally are not capable of having their sensitivity checked from the control panel over a two-wire loop, or having their sensitiv-ity adjusted ~rom the control panel without taking the system out of operation.

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A serious shortcoming of prior art systems is that loop continuity is supervised, bu~ detector presence and/or operation is not supervised. If any detector is removed and replaced by a cardboard form or some other mechanical unit to simulate detector presence, continuity along the conductor pair is maintained and the control unit does not "know" that the detector is in fact missing from the area.
Several of these shortcomings are overcome in the system of this invention which includes a bidirectional, interactive fire detection system in which only a single conductor pair is required. The control panel (or controller) selectively addresses the individual transponders, and each transponder responds when addressed. The controller also issues command signals to the addressed transponder, which command signals represent desired functions or actions to be taken by the selectively addressed transponder, which then accomplishes the functions or actions. Such command signals can con~rol the operation of various devices coupled to the transponder, such as relays, visual and/or audible indicators~ or any other device.
In the system of this invention the transponder returns a signal which identifies the type of transducer associated with that transponder. For example, the transducer could be an ionization detector, a photo-electric detector, alarm-causing switches (such as a manual pull station or a thermal switch), non-alarm-causing switches (such as an abort control for Halon, or day-night switches) or a complete zone of detectors This return signal is termed the "identification response".

The transducer also returns a "transducer response", a signal from which the controller determines the transducer sensitivity. Successive transducer response signals can be recorded to provide a continuing record of transducer sensitivity, as described in the earlier application. In the system of this invention, it is desirable to compensate for changes in the transducer response signal~
Even with the significant improvements just described~ there are areas in which such a bidirectional, interactive system can be further improved. It is highly desirable that the transponder return a reference signal from which the controller can determine that the transponder is functioning properly. This signal will be referred to as the "calibration response". In addition, it is dèsirable khat the system be equipped to compensate for changes in the calibration response signal, and further that at least certain transducers be capable of selective and remote calibration.
Also very ~mportant is that the transponder return signal, the l'transducer response" from which the con-troller determines the transducer sensitivity, be used in a manner to provide adjustable sensitivity of the transducer.
Anokher important consideration is that the improved system be useful to control a multi-zone system.
In addition, where a plurality of zones are coupled to the same two common terminals, it is desirable to identify the separate zones one from another. The "identification response" signal ~an be 7~67~

used to provide this identification of the individual zones.
Another significant consideration is that the controller of the system should be able to "read through a short", that is, discern usable and significant information whe:n a transponder is replying over the conductor pair, even though one or more additional transponders may inadvertently have its output fail in an open or shorted state when the addressed transponder 10 iS replyinq.
Yet another important consideration is that the system be a~le to poll the transponders at a time when the controlled premises are substantially un-occupied and quiescent (for example, 2:00 a.m. Sunday), to obtain and/or store various reference data.
Another desira~le advantage of the improved system is that it be able to identify the precise location of a break in one wire of the conductor pair.
Another important consideration of the improved system is that ;t be able to measure the analog representation of the signal returned from the trans-ponder with a greater accuracy than would be possible with a simple, coarse measuring arrangement, without imposing the requirement of greater accuracy on the system over the entire information-return time interval.
Yet another important consideration is that th~
new system be capable of providing a compensation signal to the controller as a function of various conditions, such as component aging, wind velocity, temperature, humidity, supply voltage at the associated transducer, and so forthO
A ~idirectional, interactive system for detectiny and indicating a predetermined condition, such as the 81 099-BKR ~7~6~3 presence of fire or products of combustion, when constructed according to the teaching of this earlier invention, need employ only two conductors. A controller and a plurality of transponders are each coupled to the same conductor pair, without any need for an end-of-line resistor or other termination unit,~or without any other means for supplying power to the transponders and/or transducers~ The controller sends out a series of signal groups or sets, with each signal group addressing a paricular transponder. One or more of the signals in a given group can be modified by the controller to pass information to the addressed transponder. Each transponder has a unique address and, when it recognizes its own address, can return information to the controller by modifying some characteristic of one signal directed back to the controller. It is important that each transponder does not depend on the proper operation of the other transponders for receiving or sending information.
Each transponder can return information concerning the identification and condition of associated transducers.
Particularly in accordance with the present invention, the controller includes means for operating upon a transponder-response signal to derive an "answer"
siynal. The answer signal is a function of both the time duration and the amplitude of the transponder-response signal. The answer signal is then examined to determine whether a particular transducer has returned a signal implying alarmf trouble, or some other condition. The sensitivity level -- or alarm threshold -- can be simply adjusted in the controller. In addition the answer signal , , ~3L7~67~
provides the desired calibration response from the transponder, in answer to the appropriate command from the controllerO The system compensates for changes in the calibration response as well as in the transducer response, and allows the individual transducers to be selectively and remotely calibrated, in real time, without affecting system operation during the calibration interval.
The answer signal is provided from each zone in a multi-zone sys-tem, and thereafter processed to provide the lQ desired information (such as alarm, trouble, "read through a short" (where a "short" means a shorted output driver), or whatever is desired). The "reading-through-a-short"
capability is included in the amplitude-responsive portion of the circuitry which produces the answer signal.
Specifically, the invention relates to a fire detection system comprising a pair of electrical conductors, a controller connected to transmit data over the electrical conductors, a plurality of transponders coupled to the conductors for returning data to the controller~ and a transducer coupled to one of the transponders. The transponder includes means for returning the data as a function of the transducer response. The controller includes means Eor storing a limit signal, means for receiving a data signal denoting transducer response from the transponder, and is characteri~ed by means connected to compare the received data signal against the stored limit signal, to provide a transducer sensitivity signal as represented by the difference between the stored limit signal for the particular transducer and the transducer response information provided by the received data signal.
In accordance with an important aspect o~ the invention, the "answer" signal is derived by using both vernier and coarse mea-suring circuits during the response period, with the vernier or fine counting only used for a portion of this response interval to enhance the accuracy of the answer signal.

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1~7~36~8 In addition, the system provides a compensation signal which can modify the processed information as a function of different variables, such as changes in wind velocity, temperature, humidity, supply voltage to a transducer coupled to a transponder, and so forth.

The Drawings In the several figures of the drawings, like reference numerals identify like components, and in those drawings:

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7~67~3 FIGURE 1 is a block diagram of a prior art fire detection system;
FIGURE 2 is a block diagram of a fire detection and signalling system constructed in accordance with the principles of the inventive system;
FIGURE 3 is a simplified schematic illustration of the controller and one transponder of the system of this invention;
FIGURES 4 and 5 are graphica1 illustrations useful in understanding operation of the system of the present invention;
FIGURES 6A, 6B and 6C are graphical illustrations, taken on a scale enlarged relative to that of FIGURES
4 and 5, useful in understanding operation of the lS present invention;
FIGURE 7 is a functional block diagram o a transponder useful with this invention;
FIGURE 8 is a schematic diagram of a transponder used with the present invention;
FIGURE 9 is a functional block diagram of an integrated circuit useful in the transponder shown in FIG. 8;
FIGURES 10 11 and 12 are graphical illustrations useful in understanding how the present invention derives information contained in a parameter of a signal;
FIGURES 13, 14 and 15 are block diagrams of one : system for implementing the present invention;

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FIGURE 16 is a schematie diagram of a Class A
arrangement, useful in understanding eertain advanta~es of this invention;
F~GURE 17 is a block diagram useul in understanding the signal--processing in the present invention; and FIGURES 18, l9A-19F, and 20A~20F are graphical illustrations useful in understanding the invention.

Detailed Description of the Invention FIG. 1 depicts a known arrangement of a plurality of detectors 20 coupled between a pair of conductors 21, 22. A control panel 23 is coupled to the conduetor pair for supervising the loop, and an end-of-line device 24 is connected across the conductor pair to provide a termination. This affords continuity of current flow along the lines. In sueh arrangement the actual detection is aecomplished by one of the deteetors sensing the fire or presence of particulate matter, going into alarm and providing a ehange in voltage or eurrent on the conductor pair which is detected at the control panel. With such an arrangement it is not possible to determine the exact location o the alarm condition, but only the loop (completed by conductors 21, 22) on whieh the alarm condition has occurred.
FIG. 2 shows a plurality of transponders 25 rather than simple detectors, conneeted to operate in conjunction with a controller 26, coupled to the same conduetor pair 27, 28 to which the transponders are eonneeted. The term "transponder" as used herein ~nd in the appended elaims signifies a unit which can eontrol -i :

.7~367~3 _g_ and/or monitor some condi.tion and/or as.sociated component which may or may not be adjacent its physi.cal location, is selectively addressed by the controller and recognizes not only- its address but additionally o~her information which may be transmitted from the controller, such as command signals for controlling the operation o the transponder itself and/or various assoc;ated devices.
In addition ~he transponder i~self transmits information, such as the transducer response and ident;fication response, back to the controller. Thus, the trans-ponders 25 truly interact with. the controller to provide a ~idirectional r interactive system. Each transponder is not a passive device which merely transmits some signal when activated by a master transmitter. It is also emphasized that there are no terminations at the end of the conductor pair 27, 28, or on either of the other pairs 31, 3~ and 33, 34 which branch off ~rom t~e main pair 27, 28 in zone 2. It will become apparent that such branching is possible without 2Q regard either to physical location or to the order i.n which each tranæponder is addressed. Such an arrangement, with no requirement for termination at the end o any conductor pair, provides a system which.is simple and economical to install and operate.
FIG. 3 depicts in simplified form the manner in which interactive signalling is accomplished between controller 2~ and one of the transponders 250 As there shown, controller 26 operates with a reference voltage V applied bet~een conductors 35, 36. Conductor 35 is coupled through a resi~tor Rl to conductor 37, which is connected over a connecting screw 38 to conductor 27. Conductor 3~ in the controller i5 connected over a screw 40 to line conductor 28. In the controller a switch Sl is coupled in parallel '~ ` - - .

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with a resistor R1. Another resistor R2, is con-nected between conductors 37 and 36. A sensing conductor 41 has one end connected between resistor R2 and conductor 37, to provide an indication of the voltage across resistor R2.
In the transponder, a resistor R3 has one end coupled to conductor 27~ and its other end coupled through another switch S2 to conductor 28. In this preferred embodiment all of resistors R1, R2 and R3 are the same resistance value. However, those skilled in the art will appreciate other values and/or ratios can be selected without departing from the principles of this invention. A command circuit 42 regulates the opening and closing of switch S1, and other components in transponder 25 (not shown) regulate the open and closed times of S2. The remaining components depicted in FIGo 3 will be described hereinafter.
The interactive communication is accomplished with the modification of at least one characteristic, such as voltage amplitude or the time duration of a signal, or the modulation of more than one such characteristic, such as both time and amplitude.
The amplitude of the voltage used in signalling is simply controlled by switches S1 and S2. Switch S1 is closed to "send" each signal or pulse in each signal group of pulses from the controller over the conductor pair 27, 28. With switch S1 closed,~ a voltage of amplitude V is passed over conductors 27, 28 to all the transponders. The duration of switch closure can also be recognized at the trans-ponder, as can the number of times switch S1 is opened and closed in each group of signals or pulses.

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7~36~13 In the case where Rl, R2 an~ R3 are of equal resistance, and with switch S1 open and switch S2 opPn, the voltage on sense conductor 41 is V/2, determined by the resistance bridge including resistances Rl and R2. Thus when transponder 25 is answering back to the controller, a voltage V/2 received on sense conductor 41 signifies switch S2 is open. When S2 is closed, while Sl remains open, this places R3 in parallel with R2, and this parallel combination is in series with Rl to determine the voltage at conductor 41. Thus with switch S2 closed, sense conductor 41 "sees" a voltage level of V/3 returned to thP controller.
Additionally the number of switch openings and closings are also readily determin~d in the controller.
Closure time of S2, while Sl remains open, can be made a function of a signal developed by an associated transducer (not shown~ r or can be made a unction of any desired information-bearing signal. By measuring the time duration of the S2 closure time, the information represented by the original signal can be determined.
Closure time of Sl can be regulated to control issuance of command signals from the controller to ~he trans-ponders.
Controller 26 derives information from the transponder replying by measuring ~he time duration of S2 closure, or time duration of voltage ~/3 appearing across R2. An important aspect of the invention i5 that significant information can still be derived by the controller, when one or more additional trans-ponders are replying concomitantly with the a~dress~d ~ransponder. To this end it is important that con~roller 26 be able to discern when --- and how much --- the voltage on sense conductor 41 falls below V/3. Ac-cordingly, ~ontroller 26 includes a signal examining .

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circuit 43 to make thls determination. In examining circuit 43 is a voltage divider circuLt 44, including four resistors 45, 46, 47 and 48 connected in series between a source of unidirectional voltage and ground.
An array 50 of comparatoxs 51, 52, and 53 is provided and connected as shown, with. one input of eac~ com-parator coupled to sense conductor 41 and the other input coupled to a connection in voltage divider circuit 44. Comparator 51 is connected to provide an output signal on conductor 54 when the signal on sense conductor 41 is V~3 or less (plus or minus a suitable tolerance~. This signifies ~t least one transponder is replying by closing its switch S2. In accordance with an important aspect of the invention, comparator 52 is connected to provide an output signal on conductor 55 when the signal on sense conductor 41 is V/4 or less (again, plus or minus an appropriate tolerance value).
Such an output signal indicates two or more transponders are replying, each closing its switch S2 and placing its respective resistor R3 in parallel with R20 By making a logical comparison of the output signals on lines 54 and 55 at any given instant, the presence of a signal on line 54 with no signal on line 55 indicates that one, and only one, transponder is then replying over the lines 27, 28. Also important is the connection of comparator 53 to provide an output signal over line 56 to command circuit 42 whenever the amplitude of the signal on sense conductor 41 is at a level of V/5, or less. This denotes three or more trans-ponders are replying, or t~ere is a short across lineconductors 27, 28. Under such. conditions the output signal on line 56 is used to shut down command circuit 42 and indicate the trouble condition. By making a logical comparison between the presence of a signal on line 55, from comparator 52, and a determination that the command circuit 42 has not been shut down, it is possible to determine that two transponders are responding ~signal on line 55) and also that a third transponder is not responding at this time, ~ecause such a condition (third transponder replying) would have been indicated by a signal returned over line 56 to shut down command circuit 42.
Those skilled in the art will appreciate that the number of comparators 'n' in examining circuit 43 of FIG. 3 (where in the illustrated embodiment n = 3), n-l number of transponders replying may be specifically identified, while n or more txansponders replying, or a short across conductors 27 and 28, is considered an unacceptable operating condition, which is identified by a signal on line 56 out of comparator 53.
To ~ettar understand the system operation, a description of ~he signal groups transmitted from the controller and returned by the transponder will be helpful. FIG. 4 indicates a series of signal groups for sequential passage over line conductors 27, 28 to the different transponders connected across these conductors. Each signal group such as the group shown under the legend 'Itransponder 1", includes the same number of pulses. In a preferred embodiment four pulses were used in each group for one transponder address, but those skilled in the art will appreciate that a different number of pulses can ~e utilized.
The extended pulse at the high amplitude le~el shown under "address 31" and the first portion of "addxess 0" indicates a reset action, and is also used to , .~ .
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7t~6 ~8 charge up a component in the transponder to provide energization of that transponder throughout the polling cycle. As will become apparent, each transponder includes a counter circuit to acc~mulate the number of pulse groUps sent over ~he line conductors, and thus recognize when its address is indicated ~y the controller. All the high level pulses ~after address 0) shown in FIG. 4 are of short duration, signifying that no command signal was sent by the controller but only different addresses, as indicated ~y the number of pulse groups.
FIG. 5 illustrates the manner in which one pulse group is modified to pass a command signal to a particular transponder. As there shown, when the seventeenth transponder is ~eing signaled, the second pulse in the group has its high level portion extended for a considerable time, which may be 40 milliseconds.
The precise time is not critical, because each transponder can include a simple timer to determine when the pulse amplitude has remained high for a minimum time, represented in FIG. 5 ~y the distance between to and tl. This time was about 20 milliseconds in the preferred embodiment, representing a "wait" period.
Because the transponder recognizes that this is the second incoming pulse, it knows the action to be taken if the pulse high is stretch beyond the "wait"
time tl. Suppose the elongation of the second pulse denotes a command to turn on a light-emitting diode (LED), or other suitable Yisual indicator. As soon as the pulse high extends heyond tl, the LED is turned on and it remains on until time t2. T~e transponder can recei~e different command signals as different high level pulses in the group are "stretched" to various lengths. Those skilled in the art will appr ciate that , ~7~6~

the controller may vary the duration of the S1 closure, and thus the duration of the high level pulses (such as the pulse between to and t2, thereby encoding information in addition to that shown in the illustrated embodiment, and thus the flexibility of the system is substantial. It is important to note that after the wait period, the appropriate component (LED), relay or other unit) is energized while the pulse is still high. This means the energy for the component is supplied from the controller over lines 27, 28, rather than being supplied by the transponder~
This will be explained more fully hereinafterO In a similar manner the transponder returns information by closing its switch S2 and thus providing a data return signal at amplitudé V/3, analogous to an extended closure of switch S2 in FIG. 3. This will be explained in more detail in connection with FIGURES 6A, 6B and 5C.
FIGURES 6A, 6B and 6C are helpful to understand the transmission of data from any of the transponders 25 to the controller 26. This is accomplished with the switch S1 of the controller in the open position, and switch S2 in the transponder is selectively closed to transmit the data. With each closure of switch S2, the voltage on sense line 41 o the control-- ler goes to V/3. The length of time that the voltage on conductor 41 remains at V~3 is a function of the controller (time duration o~ S1 open), and also the transponder ~time duration of S2 closure). The S2 closure time in turn depends upon some characteristic ., . : .
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(such as voltage amplitude~ of a detector or any other transducer associated with the transponder, or of information generated within the transponder circuit. Such associated detector ~or transducer~, or internal information generation, will ~e explained hereinafter.
FIG. 6A depicts one of the pulse groups, such as those in FIG. 4 under t~e legends "transponder 1" and "transponder 2", taken on a scale enlarged relative to that of FIG~ 4. In FIG. 6A the four pulses have "lowsl', or the low-amplitude portion of each pulse, designated 141, 142, 143 and 1440 The fourth low 144 occurs in the time duration referenced 145, and, in this embodiment, this duration is itself subdivided into three "windows" or time intervals 146, 147 and 148. It is manifest that any d sired number of windows or time intervals can be provided, depending on the degree of accuracy required. There is a transition 150 in the fourth iow, which as shown occurs in the center of window 147. This transition is within the "normalll window 147, and indicates llnormalll aperation of the component under discussion (whether an as-sociated transducer or a component internal to the transponder) providing the inormation for return in the interval 145. By way of example, this could signal the normal condition of an associated detector, or the open condition of an associated switcho If the transition occurred in the initial part of the interval 145, within time window 146, this is a low~voltage indication and could be used to indicate a txouble condition o an associated detector, or t~at a switch is not connected. If the transition ccurs wit~;n . . ~

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window 148, toward the end of time duration 145, this could be a signal, by way of example, that the as-sociated detector is in an alarm condition, or an associated switch is in the closed position. It is emphasized that the time duration of t~e initial portion of the pulse low, ~efore the transition, is made to represent the voltage amplitude at t~e trans ponder. Of course, t~is time duration could be made a function of other parameters, such as frequency or current level. In addition, transducers other than smoke detectors or switches can provide condition-indicating responses within time frame 145. For example, if a temperature-indicating transducer were connected to the transponder, a transition within window 146 could indicate a low temperature, a transi-tion within time interval 147 could signal a medium or normal temperature, and a transition within window 148 could mean a high temperature. While the transition 150 has been emphasized in the general description of FIG.
6A, it will become apparent that the time measuring scheme of the invention does not look fox the transition, as such. Rather the system continually examines, at predetermined intervals such as one millisecond, the level of the voltage during interval 145, and ac cumulates a count related to the time that the signal is at V~3 durin~ time interval 145. This provides a substantial improvement in noise immunity and measure-ment accuracy, as will be explained b~low. With the simple s~stem and respon~e indications shown in FI5.
6A, those skilled in the art will appreciate the many modîfications that can ~e made in this flexi~le system.

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The interval 145 wa~ "stretched" or elongated by 51 remaining open to provide an adequate time duration for signifying the amplitude of a related analog voltaye level. Of course, any of the other pulse lows 141, 142 or 143 could have been elongated to send back information, ~ut if elongated, the data transmitted would have ~een different. In the illustrated em~odiment, stretching or elongating the first pulse 141 permits the transponder to transmit its cali~ration information in its entirety, based on a xeference voltage. Stretching of the second low 142 permîts the transponder to provide information identifying the transducer or other component associated with the transponder.
Stretching either of the lows 143 or 144 permits the transponder to return information concerning an analog signal supplied to the transducer. In the example, only one pulse low was stretched, but more than one pulse low~can ~e elongated in a single return. Alternatively, no pulse low will be stretched if no information is desired to be returned. Thus there can be 0, 1, 2, 3, or 4 pulse lows stretched in any single group of pulses, in the embodiment where 4 pulses are used fox one transponder address.
Because the first two pulse lows 141, 142 extend ~elow line 43Q but short of line 431, the controll~r is able to determine (~y examining the voltage level on sense conductor 41~ that the transpondex switch S2 was closed. The switch closure establishes the voltage level V/3 on the sense conductor 41, and that level is within the amplitude range defined between lines 43Q and 431. At the time the third pulse 143 would ~e transmitted from the transponder, with no associated transducer or a zero signal level at that transponder, its switch S2 is not closed. ~t this time ' .7~367~

the voltage on the sense conductor i5 Y/2, determined by Rl and R2, and representea by lo~ 143 in FIG. 6A.
This response at level V/Z does provide infoxmation, namely there are no S2 closures --- in the addressed transponder or in any other ~ransponder -- at this time.
If an ionization type smoke detector were connected to the responding transponder, ~he "stretched"
pulse lsw in time interval 145 can convey information as follows. The entire time interval might have a d~ration of 32 milliseconds (ms)~ to denote a voltage amplitude range of 0 to 8 volts. Thus each millisecond of pulse duration represents 0~25 volt~ In this em~odiment the first or trouble window extends l~
ms, representing 3 volts; normal window 147 is of 8 2Q ms duration, denoting ~ volts; and the third, or alarm, window lasts for 12 ms, indicating 3 volts.
Thus with the transition 150 occuring as shown, the transponder is "telling" the controller that a voltage level of 4.0 volts has been connected to the appropriate input of the transponder from thei associated transducer, in this case an ionization-type smoke detector. The controller then operates upon this voltage level to determine how far this ~oltage (4.0 volts) is ~rom a reference level for that specific transducer to determine the state of that transducer. In addition this measured voltage level may be compared with a previously recorded voltage level from the same transducer. When the previous voltage level was recorded prior to a relatively long time period, say a week or more, the comparison can provide an indication of gradual ~ ~ i .
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changes in the detector operation/ which might be caused ~y component aging or dust acc~nulation.
By noting the extent of the change in detector operation, the change can be compensated in the system and thus avoid an erroneous indication of alarm or other condition. In addition the extent of the change caused by dust or aging can be utilized to indicate that maintenance is needed (cleaning and/or other repair of the system), to avoid an unwanted alarm or trou~le condition. By compensating for the long term changes in the detector voltaye, the controller is continually able to determine the true sensitivity, or "distance" from alarm, of each detector. This is an important advantage over the earlier described system, and over prior art systems.
In this embodiment only three windows or measuring intervals are used, to simplify the ~xplanation. If the transition 150 had occurred in the window 146, this is in the time range of 0 to 12 ms and represents a voltage amplitude of 0 to 3 volts at the detector~
A transition in this range signifies there is some trouble condition, such as an open circuit at khe connected transducer, or a circuit malfunction in the transducer. If the transition occurs in the third window 148, this signifies a voltage in the range of 5 to 8 volts within the time duration of from 20 to 32 milliseconds. A transition occurring during this time frame indicates the connected transducer is in the alarmed state, when this signal 3a is processed at the controller. That is, the con-troller compares thR returned signal to the previously stored alarm threshold reference level, and when it determines the return signal i5 a~ove this level, , 1.

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the alarm condition is indicated by the controller.
It is thus apparent that a timing arrangement is necessary in the controller to identif~v the par~
ticular duration of the signal being returned over sense conductor 41, and this will be explained in connection with FIG. 13. For the present it is sufficient to note that t~e timing is measured in the controller, and thus neit~er the transponder nor its associated transducer can initiate an alarm.
1~ In this em~odiment the controller determines and indicates when an alarm or trou~le condition is present at a specific transponder.
FIG. 6A indicates the response when a single transponder is closing its switch S2, but in FIG. 6B
the response shown occurs when another transponder (that is, a transponder which has not been addressed) has its switch S2 failed in a shorted position. That is, S2 of the other transponder remains closed through-out the time period in which information is returned by the addre~sed transponder. The ability to "read through"
this short is an important advantage of the present invention. In FIG. 6A the negative-going excursions of the first two pulses were between the lines 430 and 431.
These lines are similarly referenced in FIG. 6B. Line 430 represents a voltage level intermediate the V/2 and V/3 levels, and reference line 431 represents a voltage level intermediate the V/3 and V/4 levels. Line 432 denotes a voltage level between the V/4 and V/5 amplitudes. With ~2 of one tran~ponder closed, the resistor R3 of that transponder is in parallel with R2 of the controller, providing a voltage level of Y/3 on sense conductor 41 as has already ~een ' .

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8109~-BKR

explained. This is evident from the negative-going excursions of the firstr second and fourth pulses shown in FIG. 6A. However, with an additional transponder having its swntch S failed în the shorted position, an addit;onal R3 is paralleled with the other resistors, and this produces a negative-going excursion of the first, second and ~ourth pulses to the V/4 level as shown in FIG. 6B. It is apparent from inspection of the signal pattern in FIG. 6B that the information can still be received from the transponder and utilized, notwithstanding the shorted output condition of the additional transponder. Examination of the signal being returned is readily effected by measuring khe time duration during which the pulse amplitude remains at V~4, from ~he beginning of interval 145 to the transition 150. The method of measuring this time duration will be explained in connection with FIG. ll. By measuring this time interval the controller is able to read "through" the short and still determine the information being provided by the responding trans-ducer. This ability to read through (and also write through) a transponder's shorted output is not present in the prior systems and is an important advantage of the present invention. Sequential systems are usually dependent upon proper operation of previously addressed transponders for a subsequently addxessed transponder to return accurate information. In some systems such improper operation prevents the return of any information from suhsequently addressed transpondersO
Digital systems are usuall~ dependent upon proper operation of all transponders. If any one transponder ~s its output element shorted, no useful information can be received. If two or more transponders are sending information simultaneously, again no discernible in-formation can be received.

, :

, ;78 81099-~KR

F~G. 6C illustrates a different type o~ response, where an additional transponder is not shorted ~ut is nevertheless returning information concomitantly with the addressed transponder. Again the first two pulses reach the V/4 level, in that S2 of both transponders are closed at the same time. However, neither S2 is closed during the third pulse i~terval, and hence the controller is a~le to determine there is not a short at the second transponder, but 1~ instead both are providing information simultaneously.
During the stretched pulse interval 145, the initial portion 160 of the pulse is at the V/4 level.
However, there is a first transition 161, followed by a portion 162 at the V/3 level, and a second transition 153 before the pulse returns to the Vj2 level in the final portion 164 of this pulse. If both transitions 161, 163 are within normal window 147, as shown, the controller "knows" there is no alarm condition. Should one response fall in the 2Q alar~ region, the controller "knows'l that one detector is at the ala~m level, but at this time cannot identify the precise detector returning the alarm-level signal. Time interval 165 represents the lower analog voltage value of the two being ~5 returned, and time period 166 represents the higher of the two values. Had period 166 extended into alarm window 148, the controller would have determined that one of the t~o answering trans ponders was returning an alarm-level signal.
3a FIG. 7 depicts the functional arrangemen~ by which received signals issued by t~ controller are processed with any transponder. As there shown signals received over the line conductors 27, 28 :

:, .

~7~6~

enter the signal~power separator 60, which ef-fectively passes a d-c energizing potential difference for the transponder components over line 61 to t~e individual ones of those component~, and over line 62 to associated components (such as a detector~
~hen required. Those skilled in the art will appreciate that the line 61 may represent several conductors, such as a ground conductor, a conductor with 5 volts with respect to ground, another with 12 volts with respect to ground, and so forth.
Signals received from the line conductors are passed from the separator 60 to common bus 63, which in turn passes the signals to an address detection circuit 64 and an output command controller 65~ A plurality of address select switches represented ~y block 66 are individually coupled to address detection circuit 64. The switches are simple on-off switches, each of which can be set in the open or closed position to collectively determine the address of the specific txansponder in which the circuit is located. With five switches in the illustrated embodiment, up to 32 addresses can be individually assigned by opening and closing dif~erent ones of the switches. Thus these switches represent circuit means for determining the unique address of the transponder in which the switches are located. A
comparator or other arrangement within detection circuit 64 recognizes coincidence of the address received o~er bus 63 from the line conductoxs with the un;que address set ~ ~witches 66 and, upon recognizing this coincidence, provides an enable signal over line 67 to both the analog conditioning circuit 68 and the output command controller 65.
The analog conditioning circuit 68 includes . . ~:

7~367~3 means for recogni.zing when command information has been received from the controller, and makes th.e ap-propriate circuit connections required by such command information. Analog conditioniny ci.rcuit 68 also receives a first analog slgnal over conductor 70, which ~n t~i.s em~odiment is zero volts, and a second analog signal over conductor 71. The received analog signal can ~e any type of information-connoting signal.
By way of example, a detector 72 is shown coupled over conductor 71 to analog conditioning circuit 68. When the circuit is directed to return information to the controller concerning the analog signal r~ceived over line 71, the analog conditioning circuit transmits the response information signal, generated as a fu~ction of the analog signal received over conductor 71, over ~us 63 and the signal/power separator 60 to the line conductors, and thence to the controller. In this way the sensitivity level of the particular detector can be monitored in every cycle of operation if that is desira~le or necessary under given conditions. A
reference or calibration voltage is provided over line 73 to the analog conditioning circuit 68~
This reference voltage can be derived from a Zener diode (not shownl or other suitable unit. The reference or calibration voltage is returned to the controller when requested, so ~hat the controller circuitry can evaluate the operating condition of the transponder. For purposes of this ~xplanation, and the appended claims, line 73 represents means for providing a reference voltage.
A plurality of de~ice i.dentity switches 74 are also shown coupled to analog conditioning circuit 68. Like the other switc~es 66, identity switc~es 74 are simple open-closed or on-off switcAes, ~ut can ~e any suita~le means for completing a circuit to the most negative or most positive power rails. Such switches : ~ .
:.

~7~

can be set to provide a numeri.cal combination ~from 1 through 8, in this embodiment~ to identify the transducex type (such as detector 721 responding oYer the line conductors. By way of example, the setting of these switches can identîfy the type of connected transducer as an ionizati.on-type smoke detectox, a photoelectric-type ~moke detector, an instrument signifyi~g air velocity, a temperature-indicating unit, a mechanical s~îtch such as those used with manual pull stations t.toggle type), a momentary .switch of the type used to dump Halon, or some other device. The analog conditioning circuit also passes the signal indicating a particular command has been recognized over ~us 63 to output command controller 65, which is also enabled at this time over line 67. T~is controller can accomplish various functions. For example, one signal can regulate an electromechanical actuator 75, shown as a set-reset or on-off latching relay, to reset~ A
signal over line 76 can order this operation and the illustrated contacts 77 will be displaced rom the position shown to the alternate position (reset).
A signal from output command controller 65 passed over conductor 78 can displace the contact set to the illustrated (set) condition. Another possibility is to pass an output command signal over line 80 to illuminate a signal lamp 81, such as a light-emitting diode ~LEDI.
A basic schematic of a transponder suitable for operati.on with the present inv~ntion is shown in FI~.. 8. A pair of screw-type terminals 83, 84 connect the line conductors 27, 28 to conductors 85, 86 of ~he transponder. A surge protector 87 is coupled ~etween conductors 85, 86 to protect the transponder components from transients on the line.

, .

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,.

~7~7~

A diode 8B is coupled between signal line 85 and power line 90 o~ ~he ~ransponder. A capacitor 91 has one side coupled to conductor 86 and its other plate coupled to the common connection between power condu~tor 90 and ~he cathode of diode 88.
When a long positive-going pulse is received at the transponder, current flows through diode 88 to charge capacitor 91. The charge on capacitor 91 maintains the voltage on power conductor 90 during normal operation, when the lines are low, that is, when the voltage across conductors 27, 28 is a~ V/2 or lower. This voltage on conductor 90 is applied to the collector of an NPN type transistor 92, which is connected as a series regulator to provide a regulated output voltage on conductor 93. A
resistor 94 is connected between the collector and the base of transistor 92, and the base is also coupled through a Zener diode 95 to conductor 86.
A resistor 96 is coupled between conductor 90 and, over line 99, to input connection 10 of integrated circuit 1 (ICl).
When the voltage level on line conductors 27, 28 changes, there is a corresponding change in the amplitude of the signals passed to pin 17 of ICl.
A low-pass filter, comprised of resistor ~7 and capacitor 98, effectively blocks out high-fre~uency noise pulses. In order for ICl to receive a low-going pulse at pin 17, the signal level on conductor 27 must go low (to V/2) for at least one-half millisecond before the low-going pulse is recognized as a clock signal to IClo The voltage level on conductor 110 is compared against the voltage level on conduc~or 99, which is derived from the line vol~age (across conductors 27, 28~ is used as a reference . .

~L~.7~Çj7~

81099~BKR

signal to determine whether the clock signal is high or low~ Utilization o~ this reference signal compensates for large variations in th.e line voltage.
In the em~odiment disclosed, the system was found to function accurately despite line voltage variations from 15 to 30 volts~ a 2:1 voltage c~ange.
Other input signals are provided to ICl from the arrays o~ on-off switches 66 and 74 shown to the left of ICl. The first array includes switches 1-5 which~are the address select switches 66.
These are set ~y selective open;ng and closing before the:equipment ls energized~ to determine the unique addre~s of eac~ transponder. The second array includes switches 6-8, which are the device identity switches 74. These are set according to the particular components (not shown) which are coupled individually to the conductors 70 and 71 (FIG. 7). to provide the A and B analog input signals to the integrated circuit.
Wh.en an output command is issued by the transponder circui.try, the appropriate signal is passed over one of the conductors 76, 78 or 80 in FIG. 8. An output signal passed over line 80 energizes led 81, coupled to conductor 86. An output signal on line 78 is effective to energize the "set"
winding 101 of latching relay 75 and to close the norm~lly-open contact set 102 of this relay. An output signal over conductor 76 energizes the reset winding 103 of the relay to close the normally-closed contact set 104 of the relay. When thetransponder output circuitry pxovides a signal at pin connection 8, over line 79 to gate on NPN type transistor 10Q, resistor 89 wh.ich. in t~is em~odiment .. . .

. , . , - ~

8~

;2~-is a 4.7K resistor, is effectively connec~ed between conductors 85, 86, to pull do~n the amplitude of the voltage then being presented to the controller.
Thus the operation of transistor lOQ in response to the transistor control signals on line 79 is analogous to the opening and closing of switc~ S2 as shown in FIG. 3 and explained earlier in connection with the transponder operation. It is apparent that resistor 89 ~FIG. 82 thus corresponds to the resis~or designated R3 in the earlier discussions of the general system operation.
It is important to emphasize that an output command signal on line 79 to gate on transistor 100 is only provided during a low portion of any signal pulse. However the other a~tuating signals, to set or reset relay 75 or illuminate LED 81, are provided only during the high portion of a pulse; this is important because the transponder utilizes energy provided from the controller on lines 27, 28 to actuate these components, without imposing any drain on the energy stored in capacitor 91 which energizes the components illustrated in FIG. 8.
Other components such as variable resistor 105, fixed resistor 106, and the capacitors 107, 108 are useful in connection with the circuitry of ICl.
A general block layout of the integrated circuit is shown in FIG. 9, and a functional description of the circuitry follows. The signal pulses in each group received at the transponder are passed over line 110 to input pin 17 of ICl, and thence to clock pulse gener~tor stage 111~ This stage includes conventional pulse shaping circuitry, such as a comparator which compares the signal voltage lPvel ~L~7~i~

on line 110 against the reference voltage level on line 99. The clock pulse generator provides its output to a 2-bit counter 112 and a clock identification circuit 113. The clock identification circuit also receives a reference oscillator ~ignal from resistor 106, capacitor 108, and conductor 93, also shown in FIG. 8. A 5-~it counter 114 (,FIG. ~ is connected to receive overflow pulses over line 115 from the

2-bit counter 112. ~hen the incoming pulse remains high beyond a preset time (20 ms in t~e described embodiment~, a "stretched clock" identification pulse is passed over line 117 to a 2-to-4 line decoder circuit 118. When the incoming pulse remains high for a duration of 80 ms (in this embodiment), stage 113 provides a reset pulse over line 116 to both counters 112 and 114.
The 2-~it counter 112 provides a "clock decode"
output signal on its output conductors 120, 121.
Basically this signal idéntifies which o the several possi~le commands is to be executed by the transponder. This signal on lines 120, 121 is passed to 2-to-4 line decoder 118, the 4-channel analog multiplexer 122, and a switch logic circuit 123. The switch logic circuit is operative to provide external switch operation "memory" for two polling cycles of this transponder, should the external switch be operated for a duration less than two polling cycles. In this embodiment a polling cycle ---the time interval between two successive enable pulses being provided at the output of stage 131 --- is three seconds. Thus the memor~ duration for s~itch logic cïrcuit 123 is from 3 to 6 seconds, d~pending on the exac~ time in the polling cycle ~he'external switch is operated.

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367~
81099~BXR

Such. an external switch.can be a momentary, mechanical switch providing a signal over line 7Q and pin connection 6 to the switch logic circui.t. It is emphasized that notwithstanding the presence o~
this s~itch. and its actuation, the switch logic circuit does not store the actuation indication for subsequent transmission to the 4-channel analog multiplexer 122, unless the appropriate switch.
identification information is received over t~e three lines connected to pin connections 18, 19 and 20. These pin connections are connected to the device identity (ID~ switches 74, as already explained.
If the device ID switches 74 are in the appropriate combination to enable switch logic circuit 123, then this stage 123 is conditioned to pass the information regarding the switch actuation (at line 70) to the 4-channel analog multiplexer 122.
In the system of this invention r certain combinations of the device ID switches coupled to pin connections 18, 19 and 20 are effective to turn the switch logic stage 123 on, that is, to open the circuit between conductors 119 and 129 to the 4 channel analog multiplexer 122. In the preferred embodiment 2 of the 8 possible switch combinations were used to provide this operation. Under this condition, the switch logic circuit 123 receives the signal over line 70, pin 6, and line 119, and operates upon this signal to provide a specific state voltage ~hich is passed over line 12~ to multiplexer 122. In the other 6 combinations of the switches coupled to pins 18, 19 and 20, switch logic stage 123 effects a straight-throug~ coupling between lines 119 and 129.

1~78671~

Opexati,on of the switch logic circuit will be better understood wi.th.re~erence to FIG. 6A. W~en the device ID si.gnal denotes a two-positi.on switch.
coupled to line 70, the information received ovex line 119 from th,~ switch must be "translated" or converted to identi.fy one of the 3 possi~le states, either not connected, open or closed. Alternatively, a temperature sensor device coupled to line 70 would produce an analog output signal, and the device ID signal would dictate a straight pass-through of this information, without conversion in switch log;c stage 123.
A generator circu;t 124 is provided to develop the device identification (ID) signal and calibration (reference), signal. The ID signals are applied over a plurality of conductors represented by bus 125 to an 8-channel analog multiplexer 126. The switch ID output signal from multiplexer 126 i5 passed over line 127 to the 4-channel analog ~ultiplexer 122, which also receives the calibration voltage signal over line 73 from generator 124.
Multiplexer 122 also receives the analog A signal over conductor 71, and the analog B signal received over line 70, via lines 119 and 129, when the circuit is completed by switch logic stage 123.
The output of multiplexer 122 is passed over line 128 to a voltage-controlled one-shot stage 130, which has connections as shown to the variable resistor 105 and capacitor 107 in ~he lower right portion of FIG. 8.
A digital comparator circuit 131 (FIG. ~), is connected to receive the outputs from 5-~it counter 114, and ~he inputs from the address seIect switches 66. Upon recogn;tion of coincidence ~etween the . .

,' 6'~

unique transponder address determined by ~hese switches and the address represented by the pulses transferred from counter 114, digital comparator 131 passes an enable signal o~er line 132 to the voltage-controlled one-shot 130, and t~e enable signal is also passed over line 133 to the 2-to-4 line decoder 118. The output of the clock pulse generator on line 139, when high, resets voltage-controlled one-shot 130. When this clock output signal is low, this provides a second e.nable signal to stage 130. The voltage-controlled one-shot stage 130, upon receipt of both enable signals, functions to provide an "energize" output signal on line 134 which is amplified in the appropriate one of the output drivers 135~ a.nd passed over the output pin connection 8 of ICl. Pin 8 is selected whenever the transponder is sending information back to the controller. This is analogous to gating of transistor 100 in FIG. 8, or closure of switch S2 as explained above in connection with FIG. 3.
To select any of the other output pin connections 136 (1, 2, 3 or 4), the 2/4 line decoder 118 must provide an appropriate output signal on one of its four output lines 137. This requires three signals to decoder 118: (11 clock decode output on lines 120, lZl which selects the output driver to be energized; (2 enable signal on lin. 133, corresponding to a "trans-ponder select" signal; and (3) another enable signal (:"stretched clock."~ on line 117, which signifies the command hac indeed been i.ssued. Selection of pin 1 ma~ be used to energize an associated alarm apparatus, ~ut pin 1 is not used at this time. Selection of pin 2 indicates t~a~ LED 81 is to ~e energixed. Selection of pin 3 is equivalent to providing a signal on conductor 78 (FIG~ 7) to set the latching relay, and .

, ~ .

1~L7~6~
8109g-BKR

selection of pin 4 i.s equi~alent to providin~ a signal on conductor 76 to reset th.e latching relay~
The foregoing functional descripti.on is sufficient not only to ena~le one skilled in the art to provide an appropriate specific circuit design for IC1 in FIG.
8, but by explaining the entire functional sequence, it further enable~ one skilled in the art to implement the circuit operations with various circuits, or to regulate differ~nt ou~put functions as may be desired.
Now that the operation and circuit arrangement of the transponder has been set forth, it will be heLpful to consider the manner in which controller 26 operates upon the information returned from the transponder to derive and utilize useful signals and provide ap-propriate indications.
FIG. 10 shows in idealized form a return pulse,that is, a "stretched" pulse low similar to that designated i44 in FIG. 6A. The pulse low in FIG. 10 is designated 180, and like the other pulses occurs during a time interval of 32 milliseconds (in this embodiment) from the leading edge 181 of the pulse to the trailing edge 182 of the pulse low. The stretched low 180 includes an initial low portion 183, a positive-going portion 184, where the signal goes from the V/3 to the V/2 level, and a final portion 185. Ref~rence line 186 indicates the alarm threshold, and the lines 187, 188 depict the range of adjustable sensitivity.
As a practical matter, the actual sensitivity is represented by the diference between line 184 of the pulse signal and the alarm threshold line 186. In a preferred embodiment an 8 ~olt measurement ra~ge was depicted over 32 milliseconds, with the initial portion 183 of the pulse low representing the analog input :, .
,:

7~36~8 value from the transponder to the controller. How-ever, as a practical matter the returned information is not represented with an ideal waveform of the type depicted in FIG. 10. Rather the YariOuS transitions are distorted by the components in th~ system, to produce transitions of the type generally represented in FIG. 11.
FIG. 11 s~ows a "real-life" pulse, produced with some line capacity effects. As there shown t~e initial edge 192 of the actual response does not descend vertically ~ut follo~s a generally logarithmic curve. In this returned signal, the end or the analog or information period is represented at the positive-going portion 193, w~ich likewise is curved rather than a sharp, vertical displacement. Because these are critical portions affecting the measurement of the V/3 level portion, it would be desirable to have some vernier or more precise measurement during these two transition periods. On the "coarse range"
time scale 194 the units are sepa~ated by one milli-second (ms) intervals. It would be helpful to have another time scale, delineated as "vernier range" 195, where the units are separated in smaller intervals, such as one-half or one-quarter ms, to provide a more precise recognition of the pulse ~ransitions and thus a more accurate derivation of the exact analog value represented by the low or zero level of the returned signal. Such a measurement, for this enhanced accuracy, is made on different time scales during different time periods as represented in FIG. 12.
As there shown, ~e~ore any measurement starts the apparatus is at the 1 level or in the non-measuring mode. At time 0 ~zero millisecondsl an appropriate r~

81099~BKR

-3~-measuring apparatus is switched in, operating on the vernier scale for the first 2 milliseconds of the return pulse, represented as the 3 leveI in FIG. 12.
After the time of the initial transition, t~e measuring apparatus can operate at a more coarse level identified as level 2, until half the period or 16 milliseconds has expired. In t~is example the alarm thres~old is "po~itioned" during the following 4 milliseconds, and hence the measuring apparatus is returned to the vernier or fine measurement mode for this time interval, from 16 to 20 milliseconds. For the remainder of the pulse return period, from 20 to 32 milliseconds, the apparatus can ~e returned to, and left in, the coarse measurement mode, and switched off at the expiration sf the period. For other voltage ranges to be transmitted and different degrees of precision desired with the vernier measuring system, those skilled in the art will appreciate that changes in the voltage ranges and/or measurement intervals can readily be implemented.
FIG. 13 depicts in simplified form the arrangement in controller 26 for operating upo~ the signal returned from the transponder and passed through comparators 51, 52 to provide useful information such as "alarm", "trouble", and so forth. Basically, the system receives the signal on line 54 when one transponder is responding with a V/3 level signal, and this signal is passed over switch 200 and line 201 to two AND circuits 202, 203~ Command circuit 42 is ~onnected to regulate operation of switch 2Q0, as well as two additional three-position switches 204, 205. These latter switches are "ganged" or mechanically intercoupled ., . :

7~

81099~BKR

for simultan~ous actuation between the three positions illustrated. The circuit effects of the switching functions represented by switches 200, 2Q4 and 205 are actually accomplished, in a preferred embodiment, under the control of an algorithm stored in the memory portion of the CPU used with t~e system.
However, the mechanical switch illustration serves to depict the manner in which the signal~ and pulse trains are routed, ta~uiated and utilized to provide an appropriate "ans~er" signal from which significant, useful data are received from the appropriate trans-ponders and/or intercoupled transducers.
Switches 204 and 205 have their switch contacts designated 1, 2 and 3 to indicate mechanical positions corresponding to the showings in FIG. 12 of the off (or non-measuring mode) 1, coarse measuring mode 2, and vernier or fine measuring mode 3. Basically the system provides a pulse train from an oscillator 206 (FIG. 131 over the switches 204, 205, for passage through the ~ND circuits so long as the signal on line 201 indicates the analog information is being returned from the transponder. The low level signal 183 shown in FIG. 10 is applied over line 54 to line 201 to gate the pulse train through one of the AND circuits to the then-ef~ective counting system to provide an "answer"
signal on line 2Q7.
In more detail, oscillator 206 can be a conven-tional pulse genera~ing unit operable~ in the illustrated embodiment, to provide a pulse train at a frequency of 4,000 cycles per second. This frequency is chosen in relation to th~ duration of the returned analog signal and other considerations, including the degree of precision desired for operation in the vernier ~7~1~7~

measuring mode. The oscillator signal is provided on line 208 directly to a divide-by-4 circuit 21Q and over line 211 to position 3 (for fine counting of switch 205. The output of divide-by-4 circuit 210 is coupled over line 212 to position 2 of switch 204, the contact engaged during coarse counting. The movable contact of switch 204 is coupled over line 213 to one input of AND circuit 203, and the mo~able contact of switch 205 is coupled over line 214 to one connection of AND circuit 202. The output of AND circuit 202 is coupled over line 215 to a fine counter 216, which ac-cumulates the total number of pulses received on line 215 and provides a signal on line 217 repxesenting that total. Likewise the output of AND circuit 203 is coupled over line 218 to a coarse counter circuit 220, which accumulates the total number of received pulses and provides on its output line 221 a signal repxesenting that total. This signal is passed to a multiply-by-4 sta~e 222, which multiples this resultant signal on line 221 by 4 and provides the net result on line 223. The signals on lines 217 and 223 are then combined in adder stage 224, providing a resultant signal on line 225.
Those skilled in the art will appreciate that the counting, multiplication, division, and addition (or algebraic summation) of the various signals can be implemented with analog or digital techniques, but in this embodiment the arrangement has been implemented wi~h a digital system.
The output signal on line 225 is coupled to another adder stage 226, which also receives a compensation signal over line 227 from compensation stage 228. The precise compensation provided by stage 228 may vary as will be -explained later. The output signal from stage 226, on l~ne 207, is thus an answer signal representing the time duration during whic~ t~e s-tretched low pulse 180 .~
: :: ~

(FIG. 10) of the transponder respons~e remained low, at the V~3 level~
Common line 207 (FIG. 13~ provides ~he answer signal over line 230 to a first comparator 231, which includes an output l;ne 232 for providing an alarm-indicating signal when warranted by th~ value of the answer signal and the setting of multiple position switch 233. As shown, this switch is displaceable to one of three ~in this em~odiment~ settings ~y adjustable sensitivity stage 2~4, whic~ can be controlled over line 235 from a program stored in the memory (not shown) of ~he digitaI s~stem controlling the~operations, or over line 236 from a keyboard or other terminal (not shown) interfacing with the system~ The stored program can modify the position of switch 233, prior to comparing the answer signal, for each transponder connected in the system. This makes possible the assign-ment of any sensitivity setting to any detector on the system. Such control of switch 233 represents the function of adjustable sensitivity, as each detector can have its sensitivity adjusted from the control panel without taking the system out of operation. By chan~in~ the position of switch 233 to engage different contacts, where the number adjacent the contact denotes the value o~ ~he alarm threshold value, the answer signal on line 230 must equal or exceed this number represented by the setting to provide an alarm-indicating signal on output line 232. The numbers 65, 75 and 85 represent sensitivity thresholds on a scale of 0 to 128, a scale achieved by multiplying the 32 millisecond response interval b~ four~ The reason for t~is will become apparent in the su~sequent operational description.
The answer signal on line 207 is also applied over line 240 to another comparator stage 241, which .
', , ~ . :
.

receives another reference input signal over line 242.
This comparator is connected so ~h.at wh.en the answer signal on line 207 is less than or equal to t~.e reference signal on line 242, a trouble-indicating signal is provided on output line 243.
In operation r it is initially understood that controller 26 has "told" an addressed transponder to return information, and ~hus command circuit 42 in FIG. 13, at the beginnin~ of the response period, place.s switch 200 in the illustrated position.
Switches 204, 205 are displaced to position 3, for fine counting. Thus, at this time oscillator 206 is passing signals over line 211, switch. 205, and line 214 to one input of AND circuit 202. As soon as the fourth or stretched lo~ commences t the other input to this AND
is provided over line 201 from comparator 51, so that the pulse train is passed over line 215 and registered in counter 216. Suppose the leading edge 192 (FIG.
11~ of the responding pulse reaches the V/3 level after 1.5 milliseconds, or 6 counts on time scale 195, then the remaining 2 pulses or counts are passed through AND circuit 202 (FIG. 13) to counter 216.
This occurs because command circuit 42 maintains switches 204, 205 in position 3 for the first 2 milliseconds of the response period, after which the switch contacts are displaced to position 2 fox coarse counting. Accordingly, the AND cixcuit 202 is effectively removed from the circuit, and AND circuit 203 i5 coupled over switch 204 to stage 210. Thus the train of pulses from oscillator 206 is divided down in stage 210, and applied over line 212, switch 204 and line 213 to AND circuit 2Q3. The pulses are now effectively at 1,000 cycles, or one every millisecond, as represented on time scale 194 in FIG. 11. In that switches 204, ~L71~6~3 205 remain in position 2 during the interval from 2 milliseconds to 16 milliseconds, 14 pulses are passed over line 218 and accumulated in counter 220. This number is effectively multiplied in stage 222 to provide a value of 56 on line 223, whic~ is added in stage 224 to the value (two) previously received over line 217. At this time (16 miIliseconds~ adder staye 224 registers a count of 58, and switches 204, 205 are returned to pos;tion 3 for fine counting.
Assuming that transition 193 (FI~ occurs at 18 milliseconds, then 8 pulses are passed from the oscillator over switch 205 and AND stage 202 to register in fine counter 216, in the time interval ~etween 16 and 18 ms, and this count is passed over line 217 for addition in stage 224. These 8 pulses are added to the previous total of 58, and thus the total in addex stage 224 is now 66. At time equal to 18 ms, the gating signal is no longer provided from line 54 to line 201.
After 20 milliseconds (from time 0~ the switches 204, 205 are restored to position 2 for coarse counting, but as noted there is no longer any gating signal present to gate the pulses through AND stage 203 to the coarse counter. At this time the signal on line 225 is passed to adder stage 226.
Cornpensation stage 228 can be used to modify the preliminary result at this time. For example, if the last interrogation of the particular transponder indicated a "reference" signal voltage had risen from

4.0 volts to 4.06 volts, due to aging of the system components or other long term system change, the result on line 225 could be modified by substracting 1 from the count of 66 to provide a new count, 65, for comparison to the alarm thres`hold level and similar 7~6t78 use in the other processing stages. Accordingly, it is assumed that a count of 65 i~ the answer signal on line 207 which is passed to the comparators 231, 241.
Comparator stage 231 is connected over switch 233 to a relatively lo~ sensitivity level of 65, representing ~5/128 of R volts, or a~out 4.06 volts. Because the signal on line 230 ~a total of 65~ is equal to the 65 reference signal on the other input of comparator 231, an alarm output signal is provided at this time.
1~ operation of comparator 241 determines t~at 65 is greater than its reference ~nput 35 ~representing 2.19 volts~, and thus no trou~le signal is provided on line 243. Other processing stages will be described below in connection with FIGo 15. However, it is important to emphasize that the system illustrated in FIG. 13 provides a very high degree of precision in converting the analog signal on line 201 into the digital answer signal on line 207, even though the ine mode of counting is only employed for 2 milliseconds at the initiation of the response signal and 4 milliseconds near the middle of the response time. In a broader sense a vernier operation at a frequency higher than a reference frequency is utilized in a limited time span to provide accurate and effective measurement over a much longer time span.
FIG. 14 shows a system for obtaining an "answer"
signal on line ~07, from one of a plurality o~ zones in which different transponders and transducers are located. Each zone provides an information-denoting signal over its respective conductor 41A, 41, 41B, or 41N. This is analogous to the showing of different conductor pairs in FIG. 17 under the regulation of a plural~ty of controllers 26. Thus the various swi~ching functions shown in FIGURES 13, 14 and 15 are represented : ; , : ' ;

:

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.

7~
81099~BKR

as regulated by a command circuit, that i5, regulated by a CPU and associated program, and a plurality of controllers 26. The multipIe zones dep;cted in FIG.
14 have their respective information signals analyzed and evaluated ill the mul*~ple channels shown ~n FIG.
14, and provide on their respec~ive output conductors 251, 252~ 253 and 254 different "answer" signals representing the respective zone conditions. Command circuit 250 then activates switch 255 for sequentiaI
connection to the various output conductors 251, 254, and provides only one "answer" signal on conductor 207 at any given time.
Those skilled in the art will appreciate that the routiny of individual zone signals can be accomplished under the direction of the program stored in the controller or associated with the CPU ~not shown), to provide an operation which is the functional equivalent of the switch arrangement shown in FIG. 14.
FIG. 15 illustrates an arrangement ~or operating upon the "answer" signal developed as explained in connection ~ith FIGS. 13 and 14. Again the circuit illustration depicts the translation and/or manipulation of data to provide the desired functional output.
Such manipulation can be under the control of the stored program, but the hardware illustration is useful to explain the underlying system arrangement and operation.
FIG. 15 sho~s the "answer" signal is distributed over bus 207 for presenting "answer" data to various operational stages. The processing of this data to obtain the "alarm" and "trou~Ie" signals has already ~een descri~ed. As shown in FIG. 15, a divide-~y-16 stage 260 is coupled to line 207~ Since 128 counts represent a voltage amplitude of eight volts in this ', ' .
, ,.,, ,, 1~.7~

embodiment, then dividing 8 by 128 (as in dïvide-by-16 stage 260~ establishes a ratio for converting the answer signal on line 207 into a signal (on line 261) representing the actual transponder voltage. Thus an answer signal value of 67 (for example) would be divided in stage 260 and produce an output value of 4.2, signifyîng 4.2 volts r on line 261. When a Zener diode or other device is used to produce a calibration voltage of 4.0 volts at a transducer, this results in an answer signal of 64 on line 207, which is divided by stage 260 to prsduce a calibration voltage value of 4 . O volts on line 261.
~ nother divide-by-16 stage 262 is coupled over line 263 to the movable contact of switch 233, which receives the selected aIarm threshold voltage. Suppose switch 233 is positioned to the center or medium threshold setting, identified with a count of 75 in the drawing. This value is passed over line 263 and divided down in stage 262 to produce a value of approximakely 4.7 volts on line 264, the input connection to summation stage 265. With a voltage of 4.2 volts passed over lines 261, 266 to the negative input of stage 265, this stage provides an algebraic summation of these values, subtracting 4.2 volts from 4.7 volts to provide a resultant value of 0.5 volt on output line 267.
This resultant value is thus a measure of the trans-ducer sensitivity, as it indicates how "~ar" the transducer is from the alarm threshold. If the voltage increases another 0.5 voltr the actual voltage will reach ~he alarm threshold and provide an alarm signal on line 232. By monitoring the long-term change of sensitivity value on line 267, the controller record ran sho~ changes due to component aging, dust accumulation, and similar effects. This sensitivi~y value on line :~ ~
. ., :

~ ~ ~7~

267 is a significant measurement and provides in-for~ation at the controller which has not previously been o~taina~le.
Coupled to line 207 is another albegraic summation sta~e 27Q, whIch also receives the "answer" signal oyex Its 1nput l~ne~ 271. A storage stage 272 i5 also coupled, over l~ne 273, to ~us 2Q7. ~en the equipment is originally installed, the desired cali~xation signal is returned from each transducer, t~rough its transponder. This ini~ial calibration signal is stored ;n stage 272, provid;ng a benc~mark for sub-sequent reference. Thereafter in the "Sunday morning"
poll, a measurement taken at a low-occupancy, quiescent time such as 2:00 a.m. Sunday morning, a calibration signal is returned over lines 207, 271 to stage 270.
The original stored calibration signal is passed over line 274, and suhtracted fxom the "Sunday morning"
signal in stage 270. T~e resultant compensation signal on line 275 is a measure of the long~term changes in the circuitry, the electric conductors, and the other varia~les which affect the generation and transmission of the c~libration voltage. Thus the signals on lines 275 and 308 or a portion thereo~ can be used to modi~y the data, for example, to raise/lower the answer signal as the compensation signals change, to help mai`ntain the normal operating sensitivity of the system.
Stage 400 is coupled over line 4Ql to stage 270, to receive a si~nal denotin~ the extent of the change in the original calibration signal. A reference level ~ignal i5 applied over line 4Q2 to stage 400, and when the cali~rati`on variation signal exceeds the reference level, a "maintenance required" signal is provided on line 4Q3.
The device ID signal is derived by passing the '~
, 81099-~KR

"ans.wer" signal on line 207 over line 28Q for examination by a series of com~arators 281-288, only the first and last of which are depicted. The devi.ce identi.ty switches 74 are represented generally in FIG. 7 and in more deta~.l in FIG. 8. Th.e switch ~ettings are translated in multipiexer 126 CFIG. ~ ~.nto a s~i.tch ID signal on line 127, and then passed to the controller as ~as already been explained. Thus, the ~ignal on line 280 ~.FIG. 15) is one of elg~* different values, ~ith the precise value to ~e determined by the serie~ of comparators 281-288. For example, a "type 1" si~nal may identify a smoke detector of the ionization type, and if the signal on line 28Q îs within the range predetermined by the input signals supplied over conductors 290, 291 to comparator 281, then an output signal is provided on conductor 292 to indicate the connected device is indeed a "type 1" unit. In this way the voltages establ~.shed ~y the different comhinations o~ the ID
switch settings are e~fectively decoded and used at the controller to identify the particular device then returning information through its associated transponder.
Reference has been made to the "Sunday morning"
service, a term u~ed to indicate a sequential poll of the transponders and storage of the data returned, which. poll is at a ~requency substantially lower than the normal pollîng frequency, and is preferably taken at a time when the premises are v-.rtually unoccupied and thus guiescent. At such a time the conditions in the controlled areas will have stahilized 9 and a sample poll taken at thi:s time is useful to obtain reference information. For example, th.e respon~e volta~e of a tran~ducer can be recelved, and then comp~red to th.e initial transducer response to determine if ther~ has been any c~ange in t~is re~ponse signal.

J
~ i:
': .
' ~;7~

The three stages 300, 301 and 302 shown at the bottom o FIG. 15 are utilized only in the less-frequent poll, the "Sunday morning" po}1. The original trans.ducer response received in the first Sunday morning polI after system start-up is passed over line 303 and stored in stage 30Q, and this value is not changed thereafter. In each subsequent weekly poll, the response on line 207 is passed over line 304 to the alge~rai.c su~nation stage:301, in which the ariginal transducer response (from stage 300~ is subtracted, providi.ng a resultant output signal on line 305.
Stage 302 is a simple comparator to determine whether the amplitude of the signal on line 305 -~- and thus the extent of the transducer response change ---falls within an acceptable range. In the event theextent of the signal variation is greater than that denoting an acceptable range, a signal is provided on line 307 to indi.cate maintenance is required. Such a signal can ~e a visual signal, such as illuminating a lamp in a panel~ or an audible signal varying in some predetermined manner, or physical displacement of a "flag" or indicator, or some other indication. The precise device and manner of using the "maintenance required" signal is not critical. It is important to 2S note this is an extxemely useful signal 9 as it alerts the equipment user to the need for maintenance before a malfunction or erroneous signal can occur.

' '' .
.

Another important feature of the invention is that select;ve and remote~calibration of any trans-ponder can be effected. This:can be accomplished at any transponder, ~y changing the five address select ~witches (21-25,.FI&S. 8 and 9~ to register addxess 31. The controller is then operated to examine the cali~rat;on voltage retuxned from this transponder and, if the voltage falls within acceptable limits, to indicate this by illuminating the LED at the transponder. Other actions, such as setting of the relay, can be used to indicate the acceptable range of the calibration voltage. If the calibration rPturn is not within the preset limits, a variable resistor (105, FIGS. 8 and 9) is adjus:ted until the callbration is correct as signalled by the LED. After the correct cali-bration is verified, the address select switches are returned to their original settings.
FIG. 16 shows a general arrangement of a Class A
system with.a plurali.ty of transponders 25a and 25b connected ~or energization over the loop. Controller 26 includes a pair of conductors 311, 312 over which the voltage signals are sent and receivedO Conductor 311 is coupled to a scre~ terminal 313 and a conductor segment 314. Conductor 311 is al50 coupled over a normally-open contact set 315 to another screw terminal 316, which is connected to another conductor segment 81099 BKR ~7867B

317O Segments 314, 317 are connected h.y a short conductor segment 318 to form a continuous electri.cal circuit extendin~ from line 311, over.screw terminal 313, line se~ment~ 314, 318, 317, and scre~ terminal 316.
Line 312 is coupled over anoth.er screw terminal 320 to a line conductor segment 321. L~ne 312 is also coupled over a normally-open contact set 322 and anoth.er screw terminal 323 to a conductor segment 324.
A sh~rt segment 325 of a line conductor completes the electr~cal path.~oetween segments 321 and 324. A
resistor 326 is coupled ~etween term;nals 316 and 323, to provi.de the function of resistor R2 in FIG. 3.
In normal operation it is apparent that an energizing potential d;fference and voltage signals can be applied to all of the transponders over con-ductors 311, 312. Fox example, when the potential on l~ne 311 is positive with respect to that on line 312, current flows from line 311 over terminal 313, line segments 314, 318 and 317, transponders 25a and 25b, line segments 324, 325 and 321, and ~crew terminal 320 to conductor 312. Suppos-e however that a break occurs in line segment 317 at the location designated 327.
All transponders would no longer be in the loop over the just-described circuit. Transponders 25b still receive power, ~ut are not connected to resistor 326;
therefore data from transponders 25b cannot be received at resistor 326. Transponders 25a are no longer powered and therefore cannot function. In accordance with normal Class A operation, ~h.en-this occurs contact sets 315 and 322 would ~e closed (by means not illustrated but ~ell-kno~n and understoodl. In spite of the ~reak, the three transponders 25b to ~he rig~t in FIG.
16 are now-again connected_to resis~or 326, and trans-ponders 25a are now energized as current flows from ~7~, line 311 over contact ~et 315, screw terminal 316, and line segment 317 to the transponders 25a. In earlier arrangements the contact sets were closed and it was assumed that the transpondexs were returned to service by this operation. However, with the present invention there are advantages not o~tainable with previous Class A systems.
For Class A operation with the present invention, contact sets 315, 322 are closed, the transponders are again polled, and the addresses of the replying trans-ponders are noted. If all transponders are now replying, t~en the application of the Class A circuit restored proper operation of the system. This demonstrates that there was only one break on one or both sides of the loop.
This proof that the system is again fully operational is not available from prior art systems. Hence, the operation of the present invention with a Class A
system is a substantial advantage over prior arrange-ments.
There may be two or more breaks in the conductor loop including segments 314, 318 and 317, or in the other loop. With prior art Class A systems, the normally-open contact sets 315, 322 would be closed. However, with those earlier arrangements, there i5 not positive recognition that the contact closure, or other Class A
circuitry, has failed to restore the system, and that the transponders are non-operative. With the present invention, those transponders are polled and it is determined, from the failure to respond, that the system is inoperative by reason of a multiple break, and those transponders still not replying are specifically and individually identified.
To illustrate Class B wiring~ ~IG. 16 is modified as follows. Line segments 314 and 318 are removed, and replaced ~y a jumper 319 connec~ing screw terminals 313 and 316. ~ikewise on the other loop, line segments .

:.
. - : . : ;.

- - :

~L~7~

321 and 325 are removed, and replaced by a jumpex 320. With a single break as shown at 327, the location of the break can be determined as ~eing between two specific detectors. In the modified system of FIG. 16, the controller polls the system and notes th~e addresses of those transponders vhich do not respond. If all transponders on the loop are sequentîally addressed, then the ~reak is located between the last responding transponder and the first transponder not responding.
With additional information it i5 also possible to locate the break with non-sequentially addressed transponders.
The term "controller", as used herein and in the appended claims, refers not only to the controller 26 shown in FIG. 3, but also to a central processing unit (CPU) and its associated program. FIG. 17 illustrates the association of a CPU 330, over a bus 331, with a plurality o~ controllers designated 26, 26a, up to 26n.
A plurality of controllers ~6, 26a, . . . 26n, can share the storage and processing capability of a single CPU.
In addition, input device(s) 332, such as a keyboard, can be coupLed to the CPU to insert information such as a request for a response from a particular trans-ponder in a designated zone. Suitable output device(s) 333, such as a printer, loudspeaker, CRT display, or other arrangement can be provided to indicate the status of the data processed by the CPU. Accordingly, it is again emphasized that the term "controller" includes not only the actual control circuits but also a central processing unit, at least on a shared basis. Those skilled in the art will recognize that a CPU on a chip (integrated cîrcuit chip) can be provided with the controller circuitr~ in a compact arrangement.

:

~7~367~3 810~9-BKR

With this understanding of the controller, it is appropriate to emphasize the subs:tantial flexibility which such a controller imparts to th.e inventive system, and the ~road extent of the information included in the controller output si~nals. This will ~e set out in connection ~ith FIGS~ 18 r l9A-19F, and 20A-20F.
While these waveforms are not precisely to scale, one inch on the abcis~a of each waveform represents a time duration At 32 ms.
Considering first the showing in FIGo 18 ~ the 5 pulses there shown include 4 pulses of one pulse group representing both înformation and a particular trans-ponder address, akin ~o the four-pulse groups shown in FIGS. 6A-6C, and an elongated pulse such as the signal shown at address 31 in P'IG. 4. In FIG. 18 the low level of the pulses represents the condition with controller switch Sl (FIG. 3) open, and the high amplitude denotes the condition with Sl closed. The rise and fall of each pulse indicates a closing or an opening of switch Sl.
In FIG. 18, the rise of the first pulse at time tO is provided as switch Sl closes, and this conveys certain information. The switch closuxe and consequent pulse rise commands the previously-replying transponder to termina~e its transmission, and further "tells"
every transponder to increment its respective counter.
This is done in order that the individual pulses, and thus the pulse groups, can be tallied so that the successively addressed transponders recognize their individual addresses. After Sl has been closed, if it remaîns closed for a predetermined minimum time (repre~
sented as the duration ~etween tO and t2)l t~e command is given to the transponder to turn on its output ~l.
In the described system, this is represented by a signal at ou~put pin l of the output dxiver array 135 "
,: ' , : .:

7l3 in FIG. 9. The other output pins 2-4 are also xelated to the commands embodied in the second, third and fourth pulses in FIG. 18. Because the pin 1 connection of the output driver is not used at this~time, the fact that the command issued by stretching the first high pulse past t2 does not produce an output action.
At time t3 Sl is opened, t~e pulse goes low-, and this aCtiQn tells the addressed transponder to terminate its output ~ y removing the signal from pin 1 in FIG. 9), and aIso for the transponder to begin trans-mitting its calibratiQn data~ Note that if the pulse had gone low at time tl, this indicates that the #l output of the addressed transponder is not to be turned on.
After time t3, if switch Sl is left open in the controller, the duration of the low level signal between t3 and t4 can be up to 32 ms, in that 32 ms was the time duration chosen for the preferred embodiment.
Of course, the low level signal is continuously sampled as has been explained to determine where the transition occurs, and thus indicate the actual. value of the calibration data returned to the aontroller.
If the controller does not desire the return of calibration data from the addressed transponder, Sl is again closed after only 1 or 2 ms so that the time between t3 and t4 would thus ~e 1 or 2 ms. It is apparent that each rise and fall of every pulse in the pulse group provides information and/or commands to the addressed tran~ponder, or to all the transponders.
~t time t4 Sl is closed and th.e pulse goes high, either terminating the transmission of calibration data or preventing it, and incrementing the counters of all the txansponders. Switch.Sl is again opened at time t5 and the pulse goes low, before the time ~t6) ; :

---~ 1.'17~67~3 ~53-at which the high level pulse ~ould have commanded the transponder to turn on its output #2. In this case that would have meant driving pin 2 of driver array 135 high (FIG. 91, and illuminating LED 81 (F~GS. 7 and 8~. How~ver, t~e pulse did go lo~ at time t5, which signifies that ~ere is no action to ~e taken at the #2 LED outpùt. During the time between t5 and t8, the transponder is allowed to return the I~ data. Had the pulse gone high soon after t5, the transponder would not have been allowed to return this data.
At time t8 Sl is again closed and the pulse goes high, terminating the transmission of ID data and incrementing all the counters. The third pulse remains high, with switch Sl open, only to t9. At this instant Sl is opened, prior to the time (tlO) to which the high pulse level must be extended to command the transponder to drive pin 3 high in the driver array 135, an a~tion which commands the setting of relay 75 (FIG. 7). Thus the opening of swit~h Sl at kime t~ is in effect a command not to set the relay. The pulse remains low to tl2, an extended time during which the transponder is allowed to return information corresponding to the analog 1 input, on line 70 in FIGS. 7-9. The analog value of this signal is derived in the transponder as explained above in connection with FIGS. 11-15. At time tl2 switch Sl is again closed, sending the pulse level high in FIG. 18, terminating the response from the replying trans-ponder and incrementing all the counters.
The fourth pulse must remain high for a predetermined time interval, represented as the distance between tl2 and tl4, to order the transponder to turn on its ouput #4 and thus reset the relay. Had the pulse gone low at time tl3, the practical ef~ect is to tell the transponder not to reset the relay. However, the pulse remained `:
- , high past tl4 to time tl5, and thus the command is issued and the relay i5 reset. Between times tl5 and tl6, the transponder attempts to return the information from the second analog device, received over conductor 71 as shown in FIGS. 7-9. However, as shown in FIG. }8, it is assumed that switch Sl is closed after only 1 or 2 ms, which in effect tells the transponder not to transmit the data from the second analog de~ice. At time tl6 Sl is again closed and t~e pulse level goes high, praventing transmission of the analog 2 information and incrementing all the counters.
The four pulses just described constitute one pulse group, addressing a single transponderO Thus at time tl6 the address of the next transponder in the address sequence (which is not necessarily the next in physical locationl is commenced. The fifth pulse stays low past time t22. Had the pulse gone low by opening Sl at tl7, the effec~ would have been to command the trans-sponder not to turn on its #l output. By staying high past tl8, the command is issued to turn on the #l output.
At tl9, the timing circuit recognizes tin this embodiment) that the #l output should be terminated. The pulse remains high past t21 and t22, and at time t22 all the transponders recognize that this extended high pulse is a reset pulse, and the counters in all the transponders are thus reset. This description emphasizes the extra-ordînary amount of information and command signals packed into a single pulse group in the interactive system of this invention.
FIGS. l9A-l~F indicate one pulse group of signals from the controller in FIG. l9A, and the transponder's response or non-response to each pulse in the group in FIGS. l9B-lgE. The waveforms in FIGSo 19B-19E depict the signals at the respecti~e output pins 8 and 1-4 to `!

;

7f~7~

the right of ICl in FIG. 8 and to the xight of output driver array 135 in FIG. 9. The legend "transmitter"
at the right of FIG. 19 indicates that every time the waveform in l9B goes high, pin ~ goes high and attempts to transmit information from the transponder to the controllerO The other four outputs indicate responses developed as a functlon of the command information in FIG. l9A.
In more detail, FIG. l9A shows that at time tO Sl is closed, and t~e first pulse às initiated. Sl remains closed until tl, a time duration too short to produce a response at output pin 1, and at tl switch Sl is opened. At this time pin 8 goes high and the transponder attempts to reply, as indicated by pulse 340 in FIG.
l9B. However, at time t2 Sl is again closed to terminate t~e first command pulse, ana as the controller pulse goes high the pulse 340 at the transponder is terminated as shown. Because of the short duration of the first command pulse, that is, the high portion between tO
and tl, no act;on ~as commanded and there is no change in the output at pin 1, as depicted by FIG. l9C.
At time t2, switch Sl is closed and remains closed past the minimun time, shown at t3, required for a command for output 2 to go high. Accordingly, the output of pin 2 goes high as shown at the leading edge of pulse 341 in FIG. l9D. Pul~e 341 is that used at output pin 2 to turn on LED 81, as already described.
Thus the LED is energized between t3 and t4 while switch Sl remains closed in the controllex. At t4 switch Sl is opened, pulse 341 i5 ended, and the LED
is deenergized. At this time the transponder attempts to return information, as shown ~y pulse 342 in FIG.
l~B. However, the time duration between t4 and tS is too ~rief to allow the return of the ID data, and .~ . .
', pulse 342 is terminated when switch S1 is again closed at time t5.
The third pulse in the ~roup of FIG. 19A remains high for a short period, too brief to command any action at output pin 3~ Thus the waveform at pin 3 remains low as sh~wn ~y FIG. l9E. At time t6 S1 is opened and the third pulse goes lo~ as shown in FIG.
l9A, but not as low as the previous lo~s in the pulse group. This occurs because the third low includes the time interval during which the ~irst analog voltage is returned from a connected device. The reduced-ampli-tude low indicates there is no such device connected at the transponder then replying. Had there been a device providing a zero level signal, the third pulse low would have been at the same level as the previous lows.
At time t7 Sl is closed to commence the fourth pulse in the group. The pulse remains high past time t8, indicating a command to drive output pin 4 high and effect the corresponding action. In this case the action is to reset the associated relay, and at time t8 the leading edge of pulse 343 (FIG. l9F) is generaked at pin 4 to accomplish this reset. Pulse 343 remains high until t9, when Sl in the controller is again opened to terminate the command and at that same time pulse 343 is also terminated. The fourth low com-mences at t9, and the extension of this low allows pin 8 to go high and remain high, returning information from the second analog device, At tlO pin 8 again 3Q goes lowl simultaneousl~ with the transition in the fourth lo~ as already described, and this condition remains until tll. At tll the described pulse group is terminated and the next pulse group is ini~iated.

., ;:

7~7~

From the description in connection ~ith.FIG. 18 and FIGS. l9A-19F, the flexi~ilit~ o~ the syst~m i.n trans-mitting commands and recelving information is manifest.
However, those skilled in the art will appreciate that the system can also transmit other data information, by regulating the Sl closure time and thus t~e duration of the controller pulse highs, and also receive ~arious information from the transponders and/or associated transducers. One example of such additional data transmission is evident from considering ~IGS. l9A and l9D. Because the second pulse remained high for more than 20 ms (.the preset time in this embodiment~, represen~ed at t3, the LED was illuminated. Pulse 341 shows the duration of this illumination was about another 20 ms. Of course, the pulse 341 could have been shortened, or could have been lengthened beyond 20 ms, to conve~ differen~ information. That is, the duration of such pulse can itself sig~ify information eith.er to equipment connected at the transponder, or to personnel viewing the transpondex operatio~.
Such control of the switch Sl to pass data signals is depicted in FIGS. 20A-20F. The controller output pulses in FIG. 20A are again four in number, constituting a pulse group. The first pulse goes high at time t0 and remains high, with switch Sl closed, past tl, the minimum time to drive output pin 1 high and commence data transfer ~y producing the leading edge of pulse 345. This pulse remains high until time t2, when Sl in the controller is again opened, terminating pulse 345 at time t2. As sh.own this represents a pulse duration of about I2 ms, which can be a command to accomplish a certain function or a represen~ation of an analog value correspond;ng to the pulse time duration.

At time t2 Sl is opened, and output pin 8 goes high as the transponder attempts to reply. HDwever, after only 4 ms switch Sl is again closed, the second pulse in the transmission group is commenced and the attempted output of the transponder is terminated as pin 8 goes low at time t3.
The second pulse remains high as Sl remains closed past t4, the minimum time to command a function to pass information to output 2 of the transponder. Thus at t4 the leading edge of pulse 346 in FIG. 20D is generated, and this pulse remains high until the controller switch Sl is again opened, at time t5. This~opening of Sl terminates pulse 346, and allows pin 8 to go high as the transponder attempts to reply, but this attempt is terminated at t6 as switch Sl is closed. Thus the generation of pulse 346 represents a 32 ms data pulse forwarded to the addressed transponder.
The third pulse remalns high past t7, at which time the leading edge of pulse 347 is generated as output pin 3 goes high. The duration of this pulse between t7 and t8 denotes an 8 ms inter~al, and Sl is opened at t8 to terminate this pulse. The transponder does not attempt to reply between t8 and t9 because there is no device connected to supply the analog l signal.
2~ At t9 the fourth controller pulse is initiated as Sl is again closed, and Sl remains closed past tlO, at which time output pin 4 goes high and pulse 348 is initiated.
Pin 4 remains high until time tll, when controller switch Sl is opened to terminate pulse 348 after a 40 ms data trans-mission. At time tll output pin 8 goes high and the trans-ponder returns the pulse 350 until time tl2, where the transition occurs in the fourth low of the pulse group.
This last pulse in the group ends at tl3, at which time the counters are incremented and t~e next transponder begins to respond to the pulse group.

: ' ' .
., ~ .

.

, ~ ~

L7~6~

_5~_ Summary of TechnicaL Advantages The system of the present invention, by its use of a bidirectional, interactive communication system provides many advantages over prior art systems. As used herein and in the appended claims, a "~idirectional"
communication s~stem~is one in which commands and/or information are transmitted from a source (controller) to a receiver (transponder) over a communication path such as a conductor pair, and data and/or status in-formation may be selectively transmitted from the receiver over the same communication path to the source. The term "interactive" describes a com-munication system in which command and/or data information ~s included in a pulse group, comprising more than one pulse, transmitted from the source to the receiver and, before that one pulse group is terminated, selected data andjor status information will always be transm;tted from the receiver to the sourae, until th~ source terminates the receiver's transmission with an overriding, simultaneous transmission. The receiver does not transmit additional pulse(s), but modifies one ~or more) o~ the source-generated pulses, and this modification is translated into appropriate data b~ the source.
The unique, interactive system of this invention has many important advantages over known arrangements.
Among the more salient features are:
1. Vernier measurement in the controller to enhance accuracy of the answer signal;
2. Accurate decoding of data from the replying transponder, even though another transponder may be malfunctioning at that same time;

.

:

li7867B

81099-sKR

3. Decoding of the answer signal to rec~ver (1~ data from an associated transducer, ~21 calibration response information from the replying transponder, ox (3~ identification data from the repl~iny transponder;
4. Compensation of the transponder and trans~
ducer responses;

5. Automa~ic call for main~enance when extent of any compensation signal reaches a preset level;

6. Continuous determination of transducer sensitivity at the controller, which is remote from the transduc r itself;

7. Use of the transducer sensitivity measurement in supervising all devices, and determining --- at the controller --- when alarm and trouble conditions Occur;

8. Sensitivity adjustment for the remotely located transducer at the controller, which can be controlled constantly and automatically (e.g., by a stored program related to time of day and/or day of week) or manually (.through a keyboard). The various trans-ducers can be set to the same, or different, thresholds, and some or all of th.e transducers can have their respective thresholds changed at any time;

9. Supply of electrical power to the transponders and the transducers from the controller, over the same conductor pair which transfers the data; and

10. Unique supervision of Class A and Class B
systems~

Claim Int~erpretation A "fire detection" system, as used in the appended claims, is not limited to a system using ionization detectors, obscuration detectors, rate of temperature-rise . - , .

~7~367~

detectors, or any o.ther particular detector ype.
Rather it broadly ïncludes systems for detecting incipient and/or actual combustion.
In the appended claLms the term "connected" means a d-c connection ~etw~en two components wi.th virtually zero d-c resistance ~et~een those components. T~e term "coupled" ~ndicates there is a functional relationship ~et~een two components, with. the possible interposition of other elements ~etween t~e two components described as "coupled" or "intercoupled".
While only a particular embodiment of the invention ~as been descri~ed and claimed herein, it is apparent that various modifications and alterations of the invention may be made. It is therefore the intention in the appended claims to cover all such modifications and alterations as may fall within the true spirit and scope of the invention.
What is claimed is:

Claims (18)

1. A fire detection system comprising a pair of electrical conductors, a controller connected to transmit data over the electrical conductors, a plurality of transponders coupled to said conductors for returning data to the controller, and a trans-ducer coupled to one of the transponders, which transponder includes means for returning said data as a function of the transducer response, and in which the controller includes means for storing a limit signal, means for receiving a data signal denoting transducer response from the transponder, and characterized by means (265) connected to compare the received data signal (on 207) against the stored limit signal (on 264), to provide a trans-ducer sensitivity signal (on 267) as represented by the difference between the stored limit signal for the particular transducer and the transducer response information provided by the received data signal.

2. A fire detection system as claimed in Claim 1, in which said controller comprises means for adjusting said stored limit signal (233) to provide adjustable sensitivity of the transducer, even though the transducer may be coupled to said conductors at a location remote from said controller.

3. A fire detection system as claimed in Claim 1 or 2, in which the sensitivity is controlled constantly and automatically at the controller (e.g., by a stored program).

4. A fire detection system as claimed in Claim 1 or 2, and further characterized by means (300) for storing a first data signal denoting transducer response data from the transponder, a subsequent data signal (on 207) provides later transducer response information, and summation means (301) is connected to compare the subsequent data signal against the first data signal, to provide a transducer compensation signal (on 308) for use in the system.

5. A fire detection system as claimed in Claim 1, further characterized in that at least one of said transponders has means (73) for returning reference data to the controller as a function of transponder calibration, and the controller includes means (260,261) for receiving the data denoting calibration response of the replying transponder to indicate accuracy of the system circuitry.

6. A communication system as claimed in Claim 5, in which the replying transponder includes an indicator (81), and means (400) in the controller for recognizing when a returned calibration response signal is within preset limits and, upon such recognition, for actuating said indicator to verify that the calibration response signal from said one transponder is within said preset limits.

7. A communication system as claimed in Claim 6, wherein said one transponder includes an adjustable component (105) connected to effect a variation in said calibration response signal, thus allowing modification of the calibration response signal at the transponder until the signal is within the preset limits, as signalled by actuation of the indicator at said one transponder.

8. A communication system as claimed in Claim 5, and further characterized by means (272) in the controller for storing calibration response information, and summation means (270) for utilizing subsequent data in comparison with the stored calibration response information to provide a transponder compensation signal (on 275) for use in the system.

9. A communication system as claimed in Claim 8, and further comprising comparator means (302 or 400) coupled to the summation means (301 or 270), for providing an output signal when the magnitude of any compensation signal exceeds a preset level.

10. A fire detection system as claimed in Claim 1, in which the system is a bidirectional, interactive communication system, the controller is connected to transmit a series of signal groups (FIGS. 4,5) sequentially over the pair of electrical conductors, wherein each signal group includes a plurality of pulses, the replying transponder has means (S2) for replying to the controller by selectively modifying a portion (e.g., 184, FIG. 10) of at least one pulse transmitted by the controller and thus encoding information on said one pulse, which reply is terminated by the controller with an overriding simultaneous transmission (S1 closure), and the controller includes means (200-205) for sampling the pulse modified by the replying transponder at regular intervals to decode the information encoded on said modified pulse, and for providing the answer signal (on 207) denoting said information.

11. A communication system as claimed in Claim 10, in which the sampling of the modified pulses is conducted at a reference frequency over a sampling period, and means (206, 216) is provided for increasing the sampling rate to a second frequency higher than the reference frequency over a limited time interval which is substantially shorter than the sampling period, to enhance the accuracy of the answer signal without necessitating sampling at the higher frequency during the entire sampling period.

12. A communication system as claimed in Claim 11, in which the higher sampling rate is utilized at the beginning of the modified pulse, and in a central portion of the modified pulse.

13. A communication system as claimed in Claim 10, in which each pulse in a group includes high and low portions, each transponder includes means (S2) for lowering the voltage appearing across said pair of electrical conductors to encode the information on the low portion of one pulse, and characterized in that although a non-selected transponder has its output shorted, the controller is nevertheless capable of recovering the encoded information provided by the replying transponder (FIG. 6B).

14. A communication system as claimed in Claim 10, in which each pulse in a group includes high and low portions, each transponder includes means for lowering the voltage appearing across said pair of electrical conductors to encode the information on the low portion of one pulse, characterized in that although a non-selected transponder is replying simultaneously with a selected transponder, the controller has the capability of determining whether both answer signals, from the non-selected and selected transponders, are within an acceptable range (FIG. 6C).

15. A fire detection system as claimed in Claim 10, in which each transponder includes a counter (64), circuit means (66) determining its own unique address, and means (64) operative upon recognizing coincidence of its own address with the address represented by the number of signal groups sent by the controller to enable the transponder to respond to such additional information as may be incorporated in the signal group.

16. A fire detection system as claimed in Claim 15, in which each transponder also includes means (14) adjustable to provide an identification signal for transmission to the controller, to provide identification of the device forwarding the analog signal to the enabled transponder.

17. A fire detection system as claimed in Claim 10, in which each transponder includes a signal lamp (81) for selective illumination upon receipt of a predetermined command information signal from the controller.

18. A fire detection system as claimed in Claim 10, in which at least certain ones of said transponders include an electromechanical actuator (75) connected to be operated in response to receipt of a predetermined command information signal from the controller.