DE3117757A1 - Method and system for detecting an aerosol, such as smoke, in a gaseous medium - Google Patents

Abstract

The invention relates to a self-calibrating dimming smoke detector and to a method of operating such a detector. In this case, a light source and a photodetector are arranged in a spatial relationship to one another. The output signal of the photodetector is a function of the quantity of light which the detector detects from the light source. The analog output signal of the photodetector is converted with the aid of an analog-to-digital converter into digital signals which are then transmitted into a digital processor which is capable of periodically calibrating the detector and of carrying out the operations of taking samples or scanning between calibrations. Other sensing devices can be connected to the system, in which case the automatic self-calibrating properties are referred thereto. The use of two photodetector cells which detect the light directly from two separate light sources or indirectly from a single source produces a thermally stable system in which one cell supplies a reference output signal for the other cell.

Description

Method and system for determining an aerosol,

like smoke, in a gaseous medium The invention relates generally to dim-out smoke detectors, and more particularly to one new darkening smoke detector and a method for operating such Detector, according to which automatically belly calibration functions on a regular basis be performed.

When smoke detectors are tested, one of the applied passes Method for determining the sensitivity of each unit in a Arrange the photodetector at a certain distance from a light source, the are approx. 1.5 m (corresponding to 5 feet) in the case of the underwriter laboratory test.

The sensitivity of the detector is then expressed in darkening values with typical values in the range of 0.2 - 4; measured per foot or 30 cm. Even though however, such a device has good short-term stability has poor long-term stability and requires calibration before each test. In addition, the facility in question is affected by temperature changes as well Dirt or a film that settles on the optical surfaces of the components trains, whereby stronger transmission changes are caused than them caused by smoke alone.

The invention is accordingly based on the object of improvements in smoke detectors as well as the operating procedure for such detectors. In addition, a thermally stable, self-calibrating dark smoke detector should be used and a method for operating the detector in question can be provided.

The object indicated above is achieved by what is stated in the patent claims detected invention.

According to the invention, a self-calibrating smoke detector is provided, which comprises a light source and a photodetector which are in spatial relationship is arranged to the light source in question and which is capable of an analog electrical To generate output signal which is a function of the Is the amount of light that is determined with the help of the detector from the light source. An analog-to-digital converter is connected to the detector, the analog output signal of the detector is able to generate corresponding digital signals. With the analog-to-digital converter is connected to a digital processor, the memory devices and signal processing means which periodically re-create the detector to allow calibration and which between such new calibrations smoke sample tests allow to perform. In addition, sensing elements such as heat sensors can be connected to connected to the system and reconnected periodically on an automatic basis respectively.

be recalibrated.

According to a modification of the invention is a pair of photodetectors provided, a photodetector of which is visible to a light source passing through Smoke can be darkened, and its other detector from a second source or is visible from the first source via an attenuator to a temperature-stable System to form.

The invention also provides a method of operating a darkening smoke detector provided with a light source and a photodetector, the analog output signal of the detector in question is first converted into digital signals, which then periodically with one previously stored in a memory as a reference signal level Output signal are compared, the relevant reference signal level if necessary is corrected for an automatic calibration of the system. Anyone can do this Reference level after automatic recalibration as reference level for sample operations can be used to determine the presence or absence of smoke. Based The invention is explained in more detail below by way of example from drawings.

Fig. 1 shows in a simple schematic block diagram a self-calibrating according to the invention Breath detector.

FIG. 2 shows a view similar to FIG. 1, but with further Details the functional components of a processor shown in FIG are illustrated.

Fig. 3 shows a circuit diagram of an analog-to-digital converter can be used in conjunction with the detector.

4 shows a waveform of the characteristic output signal the circuit arrangement shown in FIG.

Fig. 5 shows a circuit diagram of a modified analog-to-digital converter.

FIG. 6 shows a waveform of the output signal in FIG. 5 circuit arrangement shown.

Fig. 7 shows a circuit diagram of yet another modification of the Analog-to-digital converter.

FIG. 8 shows a waveform of the output signal in FIG. 7 circuit arrangement shown.

Fig. 9 shows a circuit diagram of yet another analog-to-digital converter.

FIG. 10 shows a waveform of the output signal in FIG. 9 circuit arrangement shown.

Figure 11 shows a circuit diagram of a twin cell modification of the invention.

Fig. 12 shows schematically a modified double cell arrangement in a plan view.

Fig. 13 schematically shows an ionization type smoke detector, which can be used in the invention.

FIG. 14 shows a view similar to FIG. 2, but with one Modification is illustrated.

The following are the preferred embodiments of the invention described in detail. First of all, particular reference is made to FIG. 1, in which in a simple block diagram a dimming smoke detector with automatic Self-calibration properties is illustrated. The system will automatically and periodically compensate for any change in its own operating characteristics, but with the exception of those that go back to the presence of smoke. In Fig. 1, 10 generally denotes a light source, such as a light-emitting diode LED, those in spatial relation to a light-sensitive or light-sensitive Device such as a photodetector 12 is provided. The order in question is made such that a light beam 14 shines on the detector 12. at the usual or customary embodiment of a smoke detector can be air pass between the light source 10 and the photodetector 12 so that any Smoke contained in the air is carried along by the light beam 14, the relevant The beam is dampened and the smoke detector system is actuated or triggered, when the smoke density reaches a certain level.

The photodetector 12 can be any of a variety of devices from different photosensitive devices.

In the Pwgis it turned out that a photodetector with a Cadmium sulfide cell providing a peak output of 6150 A is satisfactory Produces results. This material has an average overall spectral behavior with good temperature and resistance characteristics. The photo detector 12 is an analog device capable of generating an electrical output signal is capable of which corresponds to the amount of light determined by the light source 10. During normal operation under steady state conditions with regard to temperature and in the absence of smoke, the detector output is thus over be stable for a short period of time. Any smoke coming through the beam 14 but will decrease the amount of light that hits the detector, whereby its electrical output signal will in turn be reduced.

over a long period of time, a system of the above type tends to be however, tends to be unstable due to various factors such as the Accumulation of film dirt, dust, etc. on the optical surface of the Facility 12 and due to changes in the electrical properties of the Facility due to aging, temperature and the like. Consequently the electrical output signal of the facility in question is more typical Diminish wisely over a long period of time. In the present invention changes in the operating characteristics of the system are corrected by the system is recalibrated or recalibrated on a regular periodic basis.

As shown in FIG. 1, the output of the photodetector 12 becomes an analog-to-digital converter 16 fed to the analog signals from the photodetector to convert into digital signals. From the analog-to-digital converter the digital signals are fed to a digital processor 18, which is a full computer, be a fixed link arrangement or a microprocessor, for example can.

The function of the digital processor 18 is to act as the detector to be re-calibrated or re-calibrated at discrete intervals as well as smoke samples - carry out operations between the calibrations concerned. The digital processor is connected to an alarm device 20, which is actuated or

is triggered that the smoke density between the light source 10 and the detector 12 exceeds a certain value which is periodically determined by the calibration operation is set.

A typical time span or period between the through the digital Calibrations performed by processor 18 could be set at 10 minutes, with the smoke sampling procedures take place every 5 seconds. Accordingly, the alarm level becomes adjusted every 10 minutes to reflect any changes in operating characteristics of the system to compensate.

Scanning the atmosphere for the presence of smoke or other aerosols will be used on a more frequent basis between respective calibrations namely to ensure that the presence of smoke promptly detected and the alarm is triggered.

In addition to its main function as an optical smoke detector in In the manner shown, the system could also be used to monitor the temperature by using a temperature sensitive device such as a thermistor 22 to which the analog-to-digital converter 16 is connected. The output signal the thermistor 22 represents an analog input signal for a converter 16, which in turn emits digital signals that are required for processing in the digital Processor 18 are suitable. The output signal of the thermistor can thus be used for this purpose are to trigger the alarm device 20 when a rate of temperature change or if a fixed or fixed reference temperature is exceeded. The signal could also be used by the processor to determine whether the unit in question should be recalibrated or recalibrated. The system can also be used in conjunction with an ionization type smoke detector 23 as indicated in the form of a box and in FIG. 13 closer is shown.

In order to perform automatic calibration operations in the system, the digital processor can also be used to switch between low levels the smoke formation commonly caused by a group of smokers and a real danger that is present when the smoke occurs emanates from a fire.

Although the digital processor 13 is a full computer or a fixed Linkage arrangement is used in the preferred embodiment of the invention a microcomputer, such as a single-chip microcomputer, such as the one used by him available from Motorola. One such microprocessor that is preferred for use in connection with the present invention is used, is a four-bit KS microcomputer such as that from Motorola Semiconductors Products, Inc., which is part of the MC 141000 family of microcomputers. A function block diagram of the microcomputer is illustrated in FIG. The unit in question draws are characterized by low power requirements; it works in the range of 3 to 6.5 V at 0.36 to 11.5 mW.

The input signals for the processor 18 are from the analog-to-digital converter 1G supplied, which can be operated in multiplex mode in the event that it is on various AbSühleinrichtungen is connected, as illustrated in FIG is. A device MC 144447 can be used for this purpose.

An optional input device for the microprocessor may be a manually operated push button 25 having an input connection to ground or mass connects. The function of the push button 25 is to compulsorily New or To enable re-allocation of the system. One such property is in those cases that the alarm is beneficial as a result non-dangerous States that are triggered by a transition property, for example then when there is excessive smoke from cooking when there is a fire on a hearth is kindled or the like. If the alarm is triggered under such conditions, then the system can be recalibrated by pressing button 25.

This sets a new reference level in the system.

This will turn off the alarm and the system will after the short-term smoke appeared - - - - - - -. - - - - - - -solves / automatically re-calibrate itself to the existing conditions.

Another such microprocessor is that shown in FIG Single-chip NMS microcomputer MC 3170 from Motorola. Such microprocessors comprise highly integrated circuits on a single chip that provide a substantial Flexibility with regard to the structure and the functional mode of operation of the circuit arrangement at low cost and in a compact form. The processor 18 ' 14 is an eight-bit microcomputer employing N-channel silicon gate technology using ion implantation. The microcomputer in question uses a mask-programmable 2048-By! pest value memory 24 and a 64-By @ sNotizbl-ockspeinher RAM 26 with random access and 4 input and output connections 28,30,32 and 34. In practice, two of the ports involved are like the ports 28 and 30 connected to the analog-to-digital converter 16 '. The processor also includes a programmable binary timing circuit 36 operable in three modes is, namely, in an interval timing mode, in a pulse width measuring mode and in an event counter operation. The time base for the unit in question can be created with the help of a crystal, an LC or RC circuit, and although external or internal. The system operates at low power, with the typical Performance requirement in the order of 275 mW when in use a single voltage supply arrangement, which has a voltage of 5V + 10% gives away.

For converting the analog output signal from the photodetector into digital Signals can be used in various types of analog-to-digital converters. The digital signals in question can then be processed by the digital processor 18 will. 3 to 10 are examples of several different analog-to-digital converters shown that can be used for this purpose, with the typical waveforms are illustrated which are generated by the transducer in question. The in Fig. 3 converter shown consists of a hysteresis link 40, with the a photosensitive type photodetector 42 is connected.

This link is on the one hand via a capacitor 44 connected to earth or ground, and the output of the relevant logic element is connected to one port of the digital processor 18. That on the photosensitive Means 42 incident light will control the frequency of the circuitry, which generates a train of digital pulses as illustrated in FIG are.

FIG. 5 shows a converter similar to that in FIG. 3, but with there is an exception to the extent that instead of the photoresistor device 42 a Photodiode 46 is connected to the hysteresis logic gate 48 to generate pulse shapes of the type shown in FIG. 6.

In the circuit arrangement shown in FIG. 7, any Type of photodetector device 50 connected in series with a capacitor 52, this series connection of the series connection of resistors 54 and 56 in parallel is switched. Between the resistors and the photodetector 50 is a diode arrangement 58 provided, the output signal controls the base of a transistor 60, the in turn a series of output pulses via a line 62 the in Fig. 8 type shown.

The transducer shown in Fig. 9 is a photoresist cell 64 on one side with a hysteresis device 66 and on the other side connected to the digital processor. The hysteresis device 66 is on one connected to another connection of the processor. A capacitor 68 is between the connection point of the two devices and earth or ground. The person in question Circuit arrangement generates a series of output pulses that overlap, as indicated in FIG. Each overlap shown in FIG. 10 marked with T, measured by the digital processor.

In practice, the digital processor is programmed to take smoke and exhaust measurements of the photodetector output signal on a frequent basis and calibration of the system can be made on a less frequent basis.

The digital output of the Analog-to-digital converter - which is a function of the output signal of the Photodetector acts, compared with a reference signal which is in a memory of the processor during a previous calibration operation is. Typical calibration operations can be on the order of, for example performed every 10 minutes, while smoke-sensing operations every 5 seconds could be done. If during a calibration operation the output signal of the analog-digital converter is given for example by 3000 pulses the data are accommodated in the memory area of the processor, and the previous ones Reference data will be eliminated.

During the frequent smoke-sensing operations in between is the output signal of the photodetector, which is converted into digital pulses is compared with the reference data in no difference between the data in the memory. Assuming that / memory and the data are present from the scan operation it will no alarm generated. However, if the sample data is below which is a certain value reference data, namely around / then the processor trigger the alarm device 20. The Diminished Digital Degraded Ausganyssigna, $ output signal of the converter represents a / aes photodetector, which is made up of the Presence of smoke between the light source and the photodetector results. Under assuming normal operation between calibration cycles of the system the processor automatically restores the old reference value in memory by one new benchmark for use in the next series of smoke sensing operations Accordingly, any change in the long-term operating characteristics of the Detector compensated by periodic automatic calibration of the system so that each smoke measurement is made with respect to a new, valid reference base. The accumulation of dust, dirt or a film, for example on the optical Areas of the detector over a period of time or a change in sensitivity of the detector as a result of a change in temperature or other factors automatically through the automatic periodic calibration of the system using the corrected digital processor.

The processor is now not only self-calibrating, but it can too generate a warning signal in the event that the detector is incapable for any reason is to calibrate yourself.

Such a condition could occur, for example, that one of the components of the system deteriorates beyond a usability value has an excessive film accumulated on the surface of the optical element or that a catastrophic failure of a component has occurred. A smoke detector of the specified type using a microprocessor is quite simple and extremely compact, and moreover it eliminates the need for any complex Arrangement or design in the smoke chamber. The detector shows only a minimal Change in response to different colored smoke, as with variations of gray to black. The detector level is a function of programming, and it can be an external function of the detector. The system detector would only the light source need the sensor and the processor. The processor unit itself can be located remotely from other parts of the detector; she can also be designed to accommodate a large number of units rather than just one Unit is controlled as illustrated. This can be done easily Use of known multiplex methods can be made. Because the same procedure would be used to determine the review of the operation, points in this regard the system has a high degree of determinability. The new or re-enrichment of the system does not necessarily include a full summation at the end of each Calibration cycle. For example, the data may have some digital increase a lump sum so that it compensates for a slow change in states will. In addition, the data processing operations do not need simple counting operations to be to quantify operational data insofar as others as well Quantification processes, such as successive approximations, are advantageous can be applied.

Referring now to FIG. 11, a modification of the Invention is illustrated. In this embodiment, facilities are provided to ensure operational stability regardless of changes in the operating temperature and / or Ensure line or supply voltage. That shown in FIG System uses two light sources 70 and 72, which are preferably LEDs I, ED, which are connected in series, and the cells 74 and 76 to illuminate. Each cell is part of a vibration or oscillator unit, which are the gates 78 and 80 in the upper circuit and the gates 82 and 84 in the lower circuit. Also, a resistor 86 and a Capacitor 88 in the upper circuit as well as a resistor 90 and a capacitor 92 included in the lower circuit.

The waveforms of the oscillator areas are close to the associated ones Outcomes illustrated. In practice, the capacitance of the capacitor Cl be significantly larger than the capacitance of the capacitor C2. In the illustrated Embodiment, the ratio should be over 1000 to 1.

The circuit arrangement now works in the following manner. if a 1 signal is supplied to the input terminal G1, the output signal becomes in pass a 1 state.

This change in state can be used to create an oscillator to key or to signal a counter that the oscillator has started and enumerate the input information until the G signal has a Zero state reached. Since the light-emitting diodes 70 and 72 are connected in series and Are housed in the same environment, any change in the thermal Ambient conditions and / or the supply voltage affect both LEDs, and both cells 74 and 76 are operated at the same impedance level. In the Practice can air, which may contain smoke or another aerosol, between the light emitting diodes 72 and the cell 76 enter, while the light path between the Light emitting diode 70 and cell 74 are not exposed to smoke interruption is.

Because the capacitor 88 has a higher capacitance than the capacitor 92, the number of operations at the output FO of the lower circuit is compared to the output GO of the upper circuit occur by the ratio between the two capacitors. As already indicated, there is a typical one Example of the ratio at 1000 to 1.

As any change in the ambient temperature and / or the supply voltage affects both cells, the same proportion of pulses at FO will occur. if Smoke is present the amount of the pulses at output 1110 decrease. The digital processor connected to the circuit arrangement of FIG will sample these impulses and compare them with a reference value that is periodic is updated. The regular and automatic update or recalibration procedure with the help of the processor cancels deteriorations within reasonable limits the hewing cement in the system and any remaining supply voltage or temperature fluctuations and a loss of signal strength due to the build-up of dirt on the surfaces of the optical elements.

Referring now to FIG. 12, there is another modification of the invention is illustrated. In this embodiment, there is a respect the temperature and voltage compensated smoke detector is provided, in a similar manner the detector provided in both embodiments according to FIG. The one in the present However, the smoke detector used only requires a single light source instead of two light sources. According to FIG. 12, a single light source illuminates like a light emitting diode 94, two cells 96 and 98, both in a common housing 100 are housed. The light emitting diode 94 is attached to one end of the housing and directed at a mirror 102 at the opposite end. The mirror serves to divert the light path from the light diode 94 to the cell 98, which also executed to the mirror. The cells are from the light source through a Wall 104 separated, in which an optical attenuator 106 in series with the Cell 96 is located. The function of the optical attenuator 106 is 3 to reduce the light from .der light emitting diode 94 so that the impedance of the cell 9G is similar to that of cell 98.

Each cell is connected to an analog-to-digital converter 108 or 110, which in turn on a digital processor 112 112 connected is. The processor 112 has an output leading to an alarm device 114 on, as in the basic embodiment.

A smoke detector of the type described above gives a long beam within a small room and thereby generates a strong signal change in the event that smoke passes through the chamber. The system is in equilibrium remain independent of thermal changes or line voltage changes. In operation, any scan operation will result in a gate being opened or becomes capable of transmission in order to reach the processor with a pulse burst to let its pulses counted and with the previously defined reference value can be compared in the manner described above.

In a preferred embodiment of that shown in FIG Analog-to-digital converter, better operational adaptation can be achieved by that capacitors of the same or approximately the same capacitance of, for example, 510 pF can be used. With such an arrangement, what would fall on cell 74 Light can be adjusted mechanically with the help of known devices so that about the same level occurs as caused by the light falling on cell 76. In one such a case would be F1 r F2. The digital processor would then have the sizes F1 and F2 enumerate, and after reaching a fixed size of FX, F2 would be compared. This arrangement brings greater flexibility than when using a capacitor for the generation of a key signal with itself, since the logic element is a software function were. In addition, the thermal adaptation would be improved since the cell 1 - cell 2 would be since Cl - C2 and since oscillator 1 would be r oscillator 2.

The resolution of the measurement took place under the control of the programmer, and simpler oscillator circuits can be used. If desired, the oscillator functions can be incorporated into the processor itself.

Reference is now made to FIG. 13, in which a circuit arrangement for use in the detection of smoke using ionization methods is illustrated. The circuit arrangement in question comprises an ionization chamber 116 and an insulated gate FET transistor 118. This transistor 118 emits an output signal to an analog-to-digital converter 16. When smoke in the ionization chamber gets inside, the output voltage of the relevant Device sink and cause an alarm to be triggered in the event that the Reduction exceeds a certain value.

Claims (9)

Claims 1. to a method for determining an aerosol, such as Smoke in a gaseous medium, characterized in that a) that at least one Light beam (14) is emitted through the medium in question, b) that the light energy of the light beam after passing through the medium in question in analogy electrical Signals is converted, c) that the analog signals are converted into digital signals d) that the digital signals are cyclical and at relatively long intervals quantified and the relevant quantified variable as a reference variable instead the previously recorded size is stored, e) that cyclically and relatively short intervals the digital signals are quantified and the relevant short-term quantity is compared with the reference value, f) and that an alarm is triggered in the event that that any difference between the short-term quantity and the reference quantity is definite Amount exceeds. 2. System for performing the method according to claim 1, wherein the The presence of an aerosol, such as smoke, in a gaseous medium is determined, characterized in that a) a light source (10) is provided which emits a light beam (14) able to deliver through the medium in question, b) that at a distance of the light source (10) and a light-sensitive one in the relevant light path (14) Facility (12) is provided that the intensity of the light beam (14) is able to generate corresponding analog electrical signals, c) that with the light-sensitive device (12) an analog-to-digital converter device (16) which is connected to the analog signals from the relevant photosensitive Device (12) to be converted into digital signals, d) that a digital Processing device (18) is provided with a storage device (26), which allow reference data to be stored, the processing device in question (18) with the converter device - - - - - - - - - - - - in -tung t15) connected in this way is that the output signal of the converter device is cyclical and / or relatively long periods of time (16) is compared with the reference signal in una aass cycles una / relazlv iangen clamp aas output signal of the converter device (16) measured and stored in the memory device is set as a new reference variable, e) and that with the processing device (18) an alarm device (20) is connected to generate an alarm signal in the event can make any one a certain amount during a short-term comparison excess difference is determined. 3. System according to claim 2, characterized in that an analog temperature-sensitive devices (22) generating an electrical signal on the Converter means (16) are connected in such a way that this converter means (16) the output signal of the relevant temperature-sensitive devices (16) corresponding digital signals are available. 4. System according to claim 2, characterized in that the converter device (16) a hysteresis link (405-48; 66) and a capacitor (44; .68) contains, the one with the photosensitive device (42; 46; 64) connected is. 5. System according to claim 2, characterized in that the light source a pair (G) of light emitting devices (70,72) connected in series are and the two light rays are able to emit that in each light path a light-sensitive Device (74,76) is provided and that the converter device for each light path contains a separate analog-digital circuit, which is connected to the respective light-sensitive Device (74,76) is connected. 5. System according to claim 2, characterized in that the light source a single light emitting device (94) that contains two light sensitive devices (96,98) are provided that a light reflecting device (102) in a such a position is provided that part of the light beam from the light emitting device (94) is directed to one of the photosensitive devices (98) that a optical attenuator (106) between the light output device (94) and the other photosensitive device (96) is provided and that the converter device includes separate analog-digital circuits (108,110) with the light sensitive Facilities (96,98) are connected. 7. System according to claim 2, characterized in that with the processing device (18) a manual steering device (25 ') is connected, which is used for manual New or re-enrichment of the system is used. 8. System according to claim 2, characterized in that with the converter device (16) an ionization device (23) is connected to the amount of smoke in its Proximity is able to generate a corresponding analog electrical signal, and that the relevant converter device digital Signals for the processing device (18) provides. 9. System according to claim 5, characterized in that the analog-digital circuits (108,110) are largely identical and that with the help of light control devices largely the same amounts of light can be emitted onto the light-sensitive arrangement.