DE2340041A1 - FIRE ALARM - Google Patents

Description

FATEMTAN ~ .VAI.TE

dr. ing. H. NEGENDANK · dipu-isg. H. HAUCK Dipl-Phys. W. SCHMITZ

HAMBViRG-MUNICH ADDRESS FOR SERVICE: HAMBURG 36 ■ NE UER W ALL 41

TKI .. 367428 AND 364113

TKLEGR. NEGEBAPATEST HAMBITRG CHUBB I ¹ IRB SECURITY LIMITED Munich is mozartstr. 23

TE1..138O58I1

Pyrene House, Sunbury-on-Thames , Telegh. nega patent Munich Middlesex, England

HAMBURG, August 7th

Fire alarm

Fire alarms that use optical detectors generally rely on the display of smoke. In a first type, light from a light source is incident directly on a light detector, whereby the incidence of light on the detector in the presence of smoke, and in a second type a barrier prevents the direct light transmission from the source to the detector, which light, however, in the presence of smoke passes the detector in indirect ways after diffraction and / or reflection achieved by the smoke particles. This latter form of detector is generally preferred.

Detectors in which the photosensitive device is directly exposed to a beam of light can use the Light source and the photosensitive device in

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a detector cell or may be constructed so that the photosensitive device is also exposed to the light of the environment. A difficulty with a detector that reflects the light of the environment is that the signal which is produced according to the light of the environment is such Amplitude that it becomes difficult to sense changes in light from the source. Subject a proposal A laser is used to create a narrow beam of light, this beam passing through the heated air and Other heated gases will break in the presence of fire and in some cases turn out to be photosensitive Device moved out, while creating a sharp separation of the ray is produced in the presence of fire, however, the effect of the surrounding light will still be felt, with a further disadvantage that the alignment of the laser beam is very critical and the The stability required by the laser assembly is greater than can be obtained in some buildings in which normal wall movement causes the laser beam to deviate from the target area. Although it is possible to have one to indicate such movement and to restore the beam position by means of a servomechanism is this Solution relatively expensive.

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The fire alarm according to the present invention comprises: a radiation source having a solid-state emitter which is inserted into emits radiation in a series of pulses; a radiation receiver, which is set up so that it can receive radiation from the radiation source through a gaseous medium located in between penetrated is, wherein the otradungsempfang a radiation-sensitive Includes apparatus for producing a corresponding electrical signal and that on the radiation receiver incident beam overlaps the radiation receiver over its entire circumference; one responsive to the frequency Circle for selecting a pulse signal from the detector output, resulting from the radiation pulses the radiation source results; and an alarm circuit connected to receive this pulse signal, and reacts to a change in amplitude, which has the effect of fire in the gaseous medium in between indicates.

Such a detector system does not use the change of position of the to indicate the presence of hot gases incident beam as a whole relative to the detector surface, since the broad beam always covers the entire detector surface covered, but refers to intensity fluctuations within the radiation cross-section, where

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an intensity fluctuation of the received radiation is displayed over the detector surface over time

The use of a radiation pulse source in conjunction having a frequency responsive circuit in the receiver allows most "noise" signals, i. Signals from the radiation of the environment from which the receiver output can be filtered out. Usually assigns the modulation of the beam, which is caused by the heating of the air in between by a fire a frequency between 1 Hz and 150 Hz, where the strongest modulation is in a range from 2 Hz to 25 Hz.

In the preferred alarm circuit according to the invention, a Semiconductor light source used, for example a G-allium arsenide infrared light source, this infrared light source oscillates at a frequency of 1,000 Hz, with each pulse lasting approximately 2 microseconds. To this In this way, signals caused by ambient light can be used together with those caused by the light guide Signals which have a frequency lower than 1000 Hz are filtered out, in addition to the fact that that signals at 1000 Hz are easier to amplify than a DC signal. That way, the ad from a very weak signal allows what in turn

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makes the use of a "wide beam possible. The. Impulse emission has the further advantage that the g-allium arsenide source can be made to vibrate with very high energy, since it is only switched on for a very short time will.

Since in the device according to the present invention, the radiation cross-section of the radiation receiver via his overlaps the entire circumference when the beam reaches the receiver, only minor directional fluctuations occur of the beam due to wall movements, for example only a deviating part of the beam is on the detector-receiver surface emotional. The total amount of radiation received by the detector is essentially due to such Movements not touched.

A silicon phototransistor is conveniently used as a detector. According to a preferred embodiment the phototransistor receives a constant bias by passing through an auxiliary light source with an essentially constant light level is irradiated, but alternatively an electrical bias voltage to the Base of the phototransistor can be applied. As will be explained, the preload has the effect that the The operating point of the phototransistor is shifted along its characteristic curve to a point at

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further increases in the collector current due to fluctuations of the surrounding light no longer show any significant effect on the transistor gain.

If desired, the output of the radiation-sensitive device or of another radiation-sensitive device that receives the same pulse transmitted by the emitter is used to transmit the through
Smoke-induced obscuration of the beam as well as the refraction caused by the passage of hot gases. In this way it is possible for the device to react instantly to both fires in which there is considerable heat but little smoke and to fires which develop puffs before there is sufficient heat to modulate the pulse signal.

For a better understanding of the present invention, an example of the device according to the invention will be described with reference to the accompanying drawings, voi *
those

Pig. 1 is a block diagram of the device according to the invention represents, and

Pig. Figure 2 is a circuit diagram of the H.P. amplifier stage of the recipient is.

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In Pig. 1 the radiation source 10 is a gallium arsenide iode, which emits light in the infrared part of the spectrum. In front of the diode 10 there is a shaped one biconvex lens. The optical output is represented by a diverging beam that is approximately 30 cm for a 30 m area.

The diode is set in oscillation by a free-running multivibrator, which operates at a frequency of approximately 1000 Hz works and operates a monostable pulse circuit, the pulses of which have a pulse duration of about 2 microseconds exhibit. These pulses are sent directly to a low impedance circuit 16 which controls the Feeding of the photo-emitting diode 10 controlled.

At the receiver, a phototransistor 20 is mounted behind a biconvex lens 18. Artificial light, heating and other infrared radiation of the environment is at the output of the phototransistor 20 is characterized by a direct current signal, the level of which changes with the conditions of the environment. The reinforcement of a transistor changes with the collector current up to a certain V / ert and is then essentially constant. Therefore changes under this. 7 / ert the Reinforcement of the circuit for the required ./ AC

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signal with the radiation level of the environment. With this one Receiver will have the effect of infrared radiation on an insignificant proportion of the entire environment constant illumination of the transistor is reduced by the transistor 20 by means of a photo-emitting diode 22 is flooded with a constant intensity light bias; in this way a preload is achieved, which is sufficient to bring the transistor operating range into a range of constant gain, and which enables the derivation of a strong alternating current signal despite the radiation fluctuations in the environment.

The output of the phototransistor is connected to an H.F. amplifier stage (see also Hg. 2), which Includes transistors TR1 and TR2 and a transistor TR3 in a smitter follower circuit. The resistor R7 and capacitors C5 and G4 provide AC feedback between the transistors TR2 and TR1, the capacitor C4 being the emitter resistance of the transistor TR1 decouples at high frequencies. The capacitor 07 couples out the emitter of the transistor TR2. There is also a G-I ei chs tr omko ppi ung, the consists of the resistors R8 and R5, which are coupled out through the capacitor 06. The time constants of the circuits connected to the transistors TR1 and TR2

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are selected so that this circuit is based on frequencies im Range from 100 to 330 kHz, i.e. at frequencies much higher than the 1,000 Hz pulse frequency of the Photoemitter diode 10. This response to a higher Frequency is based on the rise time of the pulses from diode 10 and the start-up time of phototransistor 20. Es allows a better differentiation from flicker frequencies out of the electrical conduction as it can be expected from a circle operating on a 1,000 Hz pulse frequency appeals to.

The remaining stages are conventional. The output of the H.F. amplifier 24 is connected to a wave-forming circuit 26 which elongates the signals and they have an integrating circuit 28 in the heat indicating channel and an integrating circuit 38 for the smoke indicating channel Channel and for the error channel. In the heat-indicating channel, the signal of the integrating Circle received by an AF amplifier 30, the frequency is selective so that signals with frequencies that caused by fire-heated air in the radiation path are going through. Signals from the audio frequency amplifier are output to a rectifier circuit 32 and thus through a delay circuit 34 to trigger a thyristor and a fire warning relay in an output

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circle 36 to excite. The time constant of circuit 34 is chosen so that the thyristor is not on transient thermal imbalances of the air in the beam path or a temporary blockage of the beam addresses.

In the breath channel, the signal on the integrating circuit 38 is applied to a first input of a level comparator 40. A second input of the level comparator 40 is fed by a quiescent signal memory 44 in which a storage capacitor receives a signal from the integrating circuit; a "divide by two" circle 42 bisects the signal applied to that second input. If the darkening by smoke reduces the output of the integrating circuit 38 to a value of 50 f * the quiescent signal level, the effect of the signal reduction occurs immediately at the first input of the comparator 40, but is delayed at the second input so that the comparator sends a signal through a delay circuit 46 having a time constant of about 3 seconds provides an output circuit 48 in which the signal triggers a thyristor and energizes the same fire alarm relay.

The error channel produces an error warning in response

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on false signals, such as "for example by an in person standing in front of the radiation path or caused by incorrect functioning of the emitter. In the error channel a differential detector 50 compares the output of circuit 38 with a signal from an error reference level circuit 52, In the event of a false signal of the type described above, causes the absence of signal pulses a discharge of the energy stored in the integrating circuit 38, the reduced voltage of this Circuit a differential amplifier 50 turns on, which an error signal through the delay circuit 54 to an output circuit 56 with a .'erraisrelays supplies. To enable signals corresponding to brief beam interruptions to be rejected, points the delay circuit 54 has a time constant of about 1 second.

A darkening of the beam would result in a smoke signal after 3 seconds. To prevent this, the error condition takes precedence and prevents the registration of a smoke signal until the error condition is cleared. The arrangement is chosen so that when a Raucha-larnisignal before the error signal has been registered, the smoke alarm is retained _o

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Claims (9)

Claims 1.] Fire alarms with one radiation source, one Radiation receiver arranged to have an emanating from and through a source gaseous medium located between the source and receiver receive penetrating radiation can, a responsive to the received radiation device to form a corresponding electrical signal and an alarm circuit responsive to the electrical signal, characterized in that that the radiation source includes a pest body emitter and a device with which The radiation is emitted in a series of pulses, the pulsating beam being the receiver of the radiation overlaps around its entire circumference, and that a frequency-selective circuit from the output the radiation-responsive device selects a pulse signal resulting from the received radiation pulses, and that the alarm circuit to an amplitude modulation in the selected pulse signal that has a fire effect on the one in between indicates the presence of a gaseous medium, responds. - 13 4098U / 0339 2. Fire alarm according to claim 1, characterized in that that the radiation source is a gallium arsenide infrared light source is. 3. Fire alarm according to claim 1 or 2, characterized in that the device responsive to the radiation is a phototransistor _o 4. Fire alarm according to claim 3, characterized in that that the phototransistor with a constant bias is provided. 5. Fire alarm according to claim 4, characterized in that the preload by an auxiliary radiation source is achieved, which is located on the radiation receiver and is arranged so that it can irradiate the phototransistor at a substantially constant level. 6. Fire alarm according to one of claims 1 to 5, characterized in that the frequency range of the frequenzselektiPiven Circle is essentially greater than the pulse repetition frequency of the emitted radiation pulses, 7. Fire alarm according to one of claims 1 to 6, characterized in that the alarm circuit includes a frequency-selective audio frequency circuit _o 409814/0339 -H- -H- 8. Fire alarm according to claim 7, characterized in that the maximum range of the audio frequency circuit in the Frequency range from 2 to 25 Hz. 9. Fire alarm according to one of claims 1 to 8, characterized in that it has a further alarm circuit which is responsive to a reduction in amplitude of the pulse signal, at least partially Indicates darkening of the emitted radiation. A098U / 0339 Blank page