DE2154537A1 - Fire alarm system - Google Patents

Description

PAT T ' H ΓΑ ^ι «Υ:« "ί Γ F = Securitas

Osnabrückj November 1st, 1971
VB / Pi

AB Securitas alarm
ileliosvägen 12
Stockholm, Sweden

Fire alarm system

The invention relates to a fire alarm system with a two-wire, with a load with finite impedance closed loop loop, a plurality of the Loop line of connected individual detectors with each a rectifying element, an impedance and one that can be switched from a rest position to an actuation position in the event of a fire Switches, which detectors are set up to only let through in one direction when the current is actuated, wherein the loop line is connected to one for generating a ™

Voltage with a first and a second polarity suitable voltage source is connected and an in the loop switched on together with the load forming a voltage divider impedance with a specific impedance Resistance and a voltage measuring device connected via the impedance with specific resistance connected is.

Modern fire notifications of this kind require that a control center connected to the loop, which is in the

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hereinafter referred to as measuring device, receives signals that are significant for the various states that can occur in the loop, namely normal state, fire, short circuit, interruption and earth fault. The most important thing for these signals is that the signal in the event of a fire is unique and is therefore lost. prevents, for example, an earth fault in the line from triggering a fire alarm. In known systems that meet this requirement, the individual detectors are relatively expensive and contain, among other things, two elements acting in only one direction to create a line νori- ^;; W to allow electricity in two directions. This makes the systems relatively complex and expensive.

Accordingly, the invention aims to provide a fire alarm system to create the, although they meet the stated requirements a clear distinction between different signal states is sufficient, only one acting in one direction Contains a link in each individual detector, making it simpler, cheaper and more reliable. Another The purpose of the invention is to create such a system that each individual detector depending on the type of detector used with a switch-on or switch-off contact in series - can work with the link acting in one direction, ™ this is in contrast to the known requirements mentioned above systems that only work with a switch-on contact in the detector that indicates the fire situation can. ,

These purposes are fully realized with the help of the invention, which is essentially based on the fact that the system is constructed as a voltage divider with an end load which is passive, conducts electricity in both directions and has the same impedance in both line directions that

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the detectors in normal operation for voltages of the first and the second polarity is the normal impedance in which the load containing branch of the voltage divider does not change that when the switch is operated at least one of the detectors the impedance of this branch has a first value for the first polarity and a different one for the second polarity, from the first deviating value and that in the event of a ground fault between the conductors of the loop line, the impedance of the Branch is reduced by the same amount for both polarities.

In the simplest version, the impedance with specific resistance and the load are ohmic resistances.

Each detector expediently contains an ohmic resistor, the member that conducts a current in only one direction and a normally open switch is connected in series while the detector is between the two wires of the Loop lines are connected in parallel to each other.

In the reverse embodiment, each detector can contain an ohmic resistor which is connected in series with a current in only one direction conducting member and a normally closed switch connected in parallel to the resistor and the member, while the detectors are connected to each other and to the loop line Are connected in series.

In both embodiments, the current conducting member in only one direction is preferably a diode.

It is particularly advantageous to use the Stron in only one direction conductive member and the associated switch to a controlled To summarize silicon rectifier, its control electrode is set up to receive control signals from a detector in the event of a fire.

-U-

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215453 '

Instead of the controlled silicon rectifier, a transistor can also be used, which in the event of a fire Control signals from a detector is set up to record.

The invention is illustrated below by means of working examples described in more detail with reference to the accompanying drawings. Show it:

Fig. 1 schematically the structure of a system with detectors, which are connected in parallel between the conductors of a loop line,

2 shows the corresponding circuit diagram for the system in its normal state,

Fig. 3 shows the corresponding circuit diagram for the system according to Fire detection,

Fig. 4 shows the corresponding circuit diagram for the system Earth fault,

Fig. 5 shows a modified fire alarm system and 6 shows a system with series-connected detectors.

In Fig. 1, a fire alarm system according to the invention is shown very schematically. The system consists of a closed loop with conductors 1 and 2, which are connected to a load R ₁ with a high specific resistance, such as 5 Kohm, which in the simplest case consists of an ohmic resistance. The closed loop is supplied with voltage from a voltage source 3. A low-ohmic resistor R n of, for example, 200 ohms is connected to the loop and to a point common to the end points of the loop, and

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across the latter is the voltage Vm across the ohmic one Resistance R "measuring device 4 switched on. the The closed loop, together with the resistor R, thus forms a voltage divider.

In the closed loop there are detectors Al, A2, A3, A4 ... An switched on. In the embodiment shown in FIG. 1, these detectors are connected in parallel to one another between conductors "1 and 2. Each individual detector, for example Al, consists of an otimic resistor R-, the member that conducts a current in one direction, for example a diode 5, and one normally open switch 6, which closes in the event of a fire, is connected in series.

The voltage source is designed so that it is uninterrupted or a DC voltage Vin is generated at a selectable point in time, the polarity of which is at a frequency of, for example 1 hz changes. An alternating voltage with any frequency can also be used; DC voltage is however, it is preferable in view of the disturbance field generated around the loop when AC power is fed in.

In the normal state of the system shown in FIG. 1 are all switches 6 open, and if the voltage source 3 feeds constant DC voltage, the rectifier 5 of the conductor 2 is positive when the pole reversal is shown Potential with respect to conductor 1. The corresponding circuit diagram for the system in the normal state is shown in FIG. The voltage VmI fed into the measuring device 4 is when the voltage source Vin has:

Vin -R _1}

VmI =: - ^±}

R ₁₊ R ₂

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It is evident that if the circuit is fed with a periodically changing direct voltage or with an alternating voltage the absolute value of VmI remains unchanged and only the sign changes.

If a fire breaks out and the switch 6 in the detector A1 is closed as a result, the corresponding circuit diagram of the system takes on the appearance of FIG. 3 and accordingly the resistor R_ is connected in parallel _{to the resistor R 1.} If you disregard the contact resistance in switch 6 and the resistance in diode 5 and assume, as before, that conductors 1 and 2 are subjected to constant DC voltage and that conductor 2 is at a higher potential than conductor 1, current is passed through the diode 6 and consequently the voltage + Vm2 measured by the measuring device 4 will be as follows:

Vin · R _{9 0Λ}

+ vm2 = - ^l)

^R l ' ^R 3

-i - + R ₉

R _{1 +} R ₃

This measured voltage Vm2 obviously deviates from the voltage VmI according to equation (1) and represents a Fire alarm voltage. So that the signal is safe as a fire alarm signal becomes recognizable, the constant DC voltage is automatically one by means of means not shown here Subject to polarity change, so that the conductor 1 becomes more positive than the conductor 2, whereby the diode 6 blocks and the measuring device the voltage - Vm2 measures, so:

Vi _n · R ₉

- Vm2 = - 3)

R _{1 +} R ₂

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By comparing these two signals, it can be clearly established from what is to be described below conceivable case will emerge that fire has broken out and the fire alarm is triggered via the conductor 7 in FIG. 1.

A condition similar to a fire is a ground fault in the Loop, but this state must not trigger a fire alarm. An earth fault of conductors 1 and 2 means that a resistor is connected in parallel to R. This resistance st a-rilfxVt in the corresponding digit The circuit diagram of FIG. 4 is illustrated by the ohmic resistor R ^. Since no switch 6 has been closed, no diode 6 is switched on either, and that from measuring device 4 measured voltage Vm3 becomes independent of the polarity of the voltage of voltage source 3, i.e. + Vm3 becomes equal -Vm3:

Vin · R

+ Vir.3 =. 4)

^R l * \

~ ^{+ R} 2

R _{1 +} R ₄

Even in the case where R = R, the fire signals according to equations (2) and (3) can easily be distinguished from the two signals according to equation (4) and the triggering of the fire alarm can be prevented when the latter "signals occur .

In the event of a simple earth fault on one conductor, the system will not be operated if the voltage source 3 and the Measuring device 4 are isolated from earth. In the case where the earthed system according to FIG. 1 with one or the other Line is grounded, signals occur that are easily distinguishable from the other conceivable signals, and therefore no fire alarm is triggered.

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If the lines 1 and 2 of FIG. 1 are short-circuited - neglecting the resistance of the lines - the voltage source 3 will be above the resistor R ", and therefore the entire voltage Vin is fed to the measuring device · +, regardless of its polarity. This error signal can also be distinguished from the fire signals, and a fire alarm is set
not triggered.

It can easily be shown that other conceivable
erroneous states in the loop, such as
Interruptions in a ladder and signs of aging
in the contacts, measurement signals can arise that are
noticeably different from other signals and therefore do not cause a fire alarm to be sent.

In the simplest case, the measuring device 4 can be a voltmeter
which is designed to transmit signals according to equations (2) and (3) to the alarm trigger line, an analog-digital converter or some other suitable device.

The voltage source 3 can be a direct current source which is able to continuously feed direct current into the loop and which is provided with a commutator that is active
an abnormal voltage condition occurs across resistor R ₉ or another member with specific resistance,
and the periodically the polarity of the DC voltage in the
Switches ladders 1 and 2. If desired, the
Change polarity even during the whole time when the system is operating normally. As mentioned, the voltage source can also be designed in such a way that it generates an alternating voltage with any frequency.

The switch 6 shown can be a mechanical contact, which is activated by means not shown here in the event of a fire

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is closed, or a transistor or a silicon rectifier, a control signal from a smoke detector or the like. Or from another conventional device receives. In the case of the application of a controlled rectifier, this Jauch replaces the rectifier shown separately 5, as shown in FIG. 5, which shows a modification of the alarm A1.

As can be seen from FIG. 5, the controlled Silicon rectifier 5a both the diode 5 as well as the Switch 6 of FIG. 1. The control electrode of the silicon rectifier 7 is normally without voltage, but on a detector (not shown here), for example a smoke gas detector, is connected which, when it occurs generated by smoke to the control electrode 7 going signal, whereby the silicon rectifier current in a Direction, i.e. in the present case when conductor 2 is at a higher potential than conductor 1.

In Fig. 6 is a system according to the. Invention shown

»Which is intended for detectors with a normally closed switch 6", which opens in the event of a fire and can, for example, be a simple fuse. The switch 6 ¹ in this case is parallel to the diode 5 'and the resistor R · in each detector, For example, the detector A ¹ I. The detectors A ¹ I - A'n are connected in this case with each other in series in the simple loop consisting of the conductor 1 ', the load resistor R' and the conductor 2 '. The voltage source 3 ¹ , which is similar to that described for the previous AusfUhrungsbeispiel is connected with its one pole to the conductor 1 'and with its other pole to one end of the resistor R ^f _ and the other end to the conductor 2'.

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The measuring device 4 ¹ , which is of the same nature as the measuring device 4 described above, is connected via the resistor R 'and is provided with a conductor 7' for triggering a fire alarm.

With the shown polarity reversal on the diodes and with steady DC voltage from the voltage source 3 'becomes appropriate positive potential is applied to the conductor 2 ', whereby in the normal state the voltage measured by the measuring device H' at a voltage Vin fed in from the voltage source 3 ' becomes as follows:

P Vin · R '

If the switch 6 ¹ interrupts, the measuring device 4 'measures the voltage under the conditions given above

Vm5 = 0 6)

This deviation from the normal value means that the voltage source, as described above, is subject to a current reversal and thereby the loop across the diode 5 'is closed P and the measuring device the voltage

Vin - R «
Vm6 = -— ⁿ

^R V ^R V ^Rf 2

will measure what is confirmation that the fire has occurred.

It can be shown that the signals Vm5 and Vm6 of the signals generated in the event of other conditions in the circuit, such as a short circuit, earth fault or wire break clearly distinguish.

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Claims (8)

2,54537 M. Pat ent an s ρ r Π ehe Fire alarm system with a two-wire loop line (1, 2; 1 ', 2') terminated with a load (R- ,; R ") with finite impedance, a plurality of individual detectors (Al - An) connected to the loop line, each with one rectifying Element (5; 5 '), an impedance (R "5 R ¹ J and a switch (6; 6'; 5a) which can be switched from a rest position to an actuation position in the event of a fire, which detectors are set up to allow current only in one direction in the actuation state , wherein the loop line is connected to a voltage source (3; 3 ¹ ) suitable for generating a voltage with a first and a second polarity and an impedance (R ";R"") with specific resistance that is connected to the loop and forms a voltage divider together with the load and a voltage measuring device (U, 4 ') connected via the impedance (Rr ₁ ; R'o) with specific resistance is connected, characterized in that the load is passive and current in both directions en is set up to let through and has the same impedance in the two line directions that the detector in normal operation for voltages of the first and second polarity the normal impedance in which the load (R- ,; F ¹ ) containing branch of the voltage divider do not change that when the switch is operated at least one of the detectors the impedance of this branch receives a first value for the first polarity and a second, different from the first fourth value for the second polarity and that in the event of a ground fault 209821/0599 BATH ORIGINAL between the conductors of the loop line is the impedance of the Branch is reduced by the same amount for both polarities, 2. Fire alarm system according to claim 1, characterized in that that the impedance with specific resistance is an ohmic resistance (R "i R'J. 3. Fire alarm system according to claims 1 and 2, characterized in that the load is an ohmic resistor (R ₁ ; R ^). 4. Fire alarm system according to one of claims 1-3, characterized in that each detector contains an ohmic resistor (R ₀ ) which is connected in series with a current in only one direction conductive member (5) and with a normally open switch (6) is switched, while the detectors (Al ... An) are connected in parallel to one another between the two wires (1, 2) of the loop line. 5. Fire alarm system according to one of claims 1-3. characterized in that each detector contains an ohmic resistor (R ') which is connected in series with a current in only one direction conducting member (5') and a normally closed switch (6 ^f ) connected in parallel to the resistor and the member is switched, while the detectors are connected in series with each other and with the loop line (1 ', 2'). 6. Fire alarm system according to claim 4 or 5, characterized in that the current is conductive in only one direction Member is a diode (5, 5 '). 7. Fire alarm system according to claim 4 or 5, characterized marked that the current is in only one direction BATH ORIGINAL 209821/0599 conductive member (5; 5 ') and the associated switch (6; 6') consist of a controlled silicon rectifier (5a), whose control electrode (7) in the event of a fire control signals from a detector is set up * 8. Fire alarm system according to claim 4 or 5, characterized characterized in that the current in only one direction conductive member and the associated switch from one There are transistor, which is set up to receive control signals from a detector in the event of a fire. 20982 1/0599