RU2275688C2 - Combined fire alarm - Google Patents

Abstract

FIELD: engineering of fire alarms, namely - combined fire alarms, possible use for detecting fire by increase of environmental temperature and/or appearance of smoke in place of alarm mounting.

SUBSTANCE: problem is solved by mutual decrease of thresholds during detection of two fire factors, meaning joint consideration of these factors during taking of decision about forming of alarm notification.

EFFECT: increased reliability of fire detection at early development stage.

4 cl, 5 dwg

Description

The invention relates to a fire alarm technique.

Fire detectors are known for detecting a fire due to several related factors. A device for detecting fire [1] is known, which reacts to the appearance of two factors, for example, smoke, as well as an elevated temperature at the facility. This detector contains first and second sensors, outputs connected to the corresponding inputs of the first and second signal processing units, the first outputs of which are connected to the first and second inputs of the OR logic element, the second outputs of the first and second signal processing units are connected to the first and second inputs of the logical the "And" element, the output of which is connected to the third input of the "And" logical element, the output of which is connected to the input of the alarm notification generator.

When the detector is working, the combination of smoke and heat detection channels is carried out according to the 2I-OR logic circuit. In this case, the formation of the “Fire” notice occurs when any controlled parameter (concentration of smoke particles or temperature) reaches the corresponding high threshold, as well as when both controlled parameters of other, lower threshold values are reached. Such a detector construction makes it possible to increase the probability of detecting both a fire in which one of the detected factors is dominant - smoke or heat, and a fire in which both of these factors are present but not sufficiently intense.

The disadvantage of the detector [1] is that the use of independent fixed thresholds does not allow in practice to take into account the variety of conditions under which a fire arises and develops, and the related features in the dynamics of changes in related factors. This leads to an increase in the likelihood of false alarms, as this increases the influence of interference, which can cause false detection by a fire detector. Thus, the reliability of fire detection at an early stage of development by the detector [1] is insufficient.

Partially indicated disadvantages are eliminated in the fire detection device [2], which is the closest to the inventive combined fire detector. The structural diagram of the prototype device is presented in figure 1.

The device comprises a first smoke sensor 1 and a second temperature sensor 2, the outputs of which are connected to the inputs of the signal processing unit 5 through the corresponding first 3 and second 4 analog-to-digital converters, the first output of which is connected to the input of the first 3 analog-to-digital converter and the first smoke sensor 1 , the second output of the signal processing unit 5 is connected to the input of the second 4 analog-to-digital converter and the second temperature sensor 2, and the third output of the signal processing unit 5 is a signal output from broadcaster.

The fire notification in the device [2] is generated according to the OR logic when one of the controlled factors reaches the threshold level, as well as when both factors grow together if the calculated coefficient of their mutual correlation reaches the set threshold value.

The value of the cross-correlation coefficient R is calculated by the formula

Where

X _i , Y _i - the measured values of the level of smoke and temperature, respectively, at the i-th time;

,

- средние значения уровня задымленности и температуры соответственно;

,

- average smoke levels and temperatures, respectively;

N is the number of measurements.

Thus, only if there is a steady joint increase in controlled factors, it is possible to reduce the time a fire is detected by the device [2]. However, it is known [3] that the unsteady rapidly changing value of factors (fluctuations in smoke and temperature) is characteristic of the initial stage of a fire. Therefore, in this period, due to a significant standard deviation (the denominator in expression (1)), the value of the cross-correlation coefficient may be small and will not cause the device to trip [2]. In accordance with mathematical theory, the use of the correlation coefficient as a measure of dependence is justified only when the joint probabilistic distribution of the pair of factors used is normal or approximately normal [4]. Otherwise, the correlation coefficient may be zero, even when the factors are connected by a strict functional dependence (different from linear). Since the combustible load on a real object, as a rule, is distributed unevenly and its individual types are distinguished by the ability to smoke and release heat energy, significant non-linear fluctuations of these factors are possible during the development of a fire [5]. Thus, the proposed method of reducing the time of fire detection does not provide sufficient reliability in practice.

The problem to be solved in the inventive combined fire detector is to increase the reliability of fire detection at its early stage of development.

Reducing the detection time in the inventive device is achieved by a mutual reduction of the thresholds when two fire factors appear, that is, a joint consideration of these factors when deciding on the formation of a fire notice.

Changing the detector threshold during the detection process is known in the fire alarm technique. For example, it is available in the thermal maximum differential detector IP 101-2 [6]. The structural diagram of such a detector is presented in figure 2.

The first thermosensitive element 1, made on the thermistor 10, equipped with a heat receiver and placed outside the detector housing, due to various heat transfer conditions, has a heating time constant less than the same second thermosensitive element 2 on the thermistor 11, but located inside the housing. With a slow increase in ambient temperature with a time constant that is much larger than the heating time of the thermistors and the first 1 and second 2 thermosensitive elements, their resistance decreases proportionally. In this case, the voltage at the first measuring input of the comparator 4 with respect to the voltage at its second reference input, formed by resistors 13-15 of block 3, changes due to an increase in voltage across the resistor 12. At a temperature of + 60 ° C, the comparator 4 opens, forming a control signal on the input of the memory unit 6. The memory unit 6 opens and the current flowing through it increases sharply, including using the electronic key 7, the indicator light 9 in the continuous mode of illumination, leading to increased current consumption of the detector from the alarm loop. The detector is triggered as maximum, forming a notice of excess of the ambient temperature of the set threshold value. With a rapid increase in air temperature, the resistances of the semiconductor thermistors 10, 11, due to the difference in their heating time constants, decrease disproportionately, accelerating the voltage increase at the first measuring input of the comparator 4. After reaching the voltage value of the set value, the comparator 4 opens, causing the unit 5 to generate a notification fire.

Thus, in the IP 101-2 detector [6], with increasing temperature, the reference voltage at the input of the comparator increases, and inversely with the rate of temperature increase. The change in the reference voltage is associated with one controlled factor (temperature). In the claimed device, the value of the reference voltage at the input of the comparator that controls one factor decreases under the action of a signal indicating an increase in the intensity of another factor, and is directly proportional to this signal.

Therefore, the novelty of the proposed technical solution in comparison with the device [6] is significant.

In the inventive combined fire detector, the task is solved by the fact that in the known device [2] containing a first smoke sensor, a second temperature sensor and a signal processing unit, the first output of which is connected to the first smoke sensor, and the second output of the signal processing unit is connected to the second sensor temperature, a reference voltage generation unit, a comparator unit and an alarm notification generator are introduced, the output of the first smoke sensor is connected to the first input of the formation unit voltage and the first input of the comparator unit, the output of the second temperature sensor is connected to the second input of the reference voltage generating unit and the second input of the comparator unit, the output of which is connected to the input of the signal processing unit, the third output of which is connected to the input of the alarm notification generator, the output of which is a signal output detector.

The reference voltage generating unit contains the first and second reference voltage drivers, the first input of the reference voltage generating unit is the input of the second reference voltage driver, the output of which is the second output of the reference voltage generating unit, the second input of the reference voltage generating unit is the input of the first reference voltage generating device, the output of which is the first output of the block forming the reference voltage.

The comparator unit contains the first comparator, the second comparator and the logical element “OR”, the outputs of the comparators are connected to the inputs of the logical element “OR”, the output of which is the output of the unit of comparators, the first and second inputs of the unit of comparators are respectively the output of the first smoke sensor and the output of the second temperature sensor , the third and fourth inputs of the block of comparators are respectively the first and second outputs of the block forming the reference voltage.

The signal processing unit contains a setting pulse generator, a counter and a pulse generator, the first input of the counter is the input of the signal processing unit, and its output is the third output of the signal processing unit, the output of the setting pulse generator is connected to the second input of the counter, the first output of the pulse generator is connected to the third input counter, and the remaining two outputs of the pulse generator are respectively the first and second outputs of the signal processing unit.

In the inventive device, the known blocks, as well as comparators in the block of comparators can be performed identically to a fire detector [7].

Figure 3 shows a diagram of the inventive combined fire detector.

The detector comprises a first smoke sensor 1, a second temperature sensor 2, a reference voltage generating unit 3, a comparator unit 4, a signal processing unit 5, and an alarm notification generator 6.

The output of the first smoke sensor 1 is connected to the first input of the reference voltage generating unit 3 and the first input of the comparator unit 4, the output of the second temperature sensor 2 is connected to the second input of the reference voltage generating unit 3 and the second input of the comparators 4, the output of which is connected to the input of the signal processing unit 5, the first output of which is connected to the input of the first 1 sensor, the second output of the signal processing unit 5 is connected to the input of the second 2 sensors, the third output of the signal processing unit 5 is connected to the input of the STUDIO alarm signal 6 whose output is the signal output device.

The first smoke detector 1 contains a power amplifier 7, the outputs of which are connected to the emitting LED 8, and a light energy receiver in the form of a photodiode 9, the outputs are connected to a signal amplifier 10. The input of the power amplifier 7 is the input of the first smoke sensor 1, the output of the signal amplifier 10 is the output smoke sensor 1.

The second temperature sensor 2 contains a thermistor 11 connected to the amplifier 12, the output of which is the output of the temperature sensor 2, and the input is the control input of the amplifier 12.

The reference voltage generating unit 3 contains the first 13 and second 14 reference voltage drivers, the first input of the reference voltage generating unit 3 is the input of the second reference voltage driver 14, the output of which is the second output of the reference voltage generating unit 3, the second input of the reference voltage generating unit 3 is an input the first driver of the reference voltage 13, the output of which is the first output of the block forming the reference voltage 3.

The comparator unit 4 contains the first comparator 15, the second comparator 16 and the logical element "OR" 17, the outputs of the comparators 15, 16 are connected to the inputs of the logical element "OR" 17, the output of which is the output of the unit of comparators 4, the first and second inputs of the unit of comparators 4 are respectively, the output of the first smoke sensor 1 and the output of the second temperature sensor 2. The third and fourth inputs of the comparator unit are respectively the first and second outputs of the unit for generating the reference voltage 3.

The signal processing unit 5 comprises a set pulse generator 18, a counter 19 and a pulse generator 20. The first input of the counter 19 is the input of the signal processing unit 5, and its output is the third output of the signal processing unit 5. The output of the set pulse generator 18 is connected to the second input of the counter 19 , the first output of the pulse generator 20 is connected to the third input of the counter 19, and the other two outputs of the pulse generator 20 are respectively the first and second output of the signal processing unit 5.

Voltage diagrams characterizing the operation of the detector are shown in figure 4, 5.

Combined fire detector operates as follows.

Under normal environmental conditions, after turning on the power, the generator of impulse pulse 18 brings the counter 19 to its initial state, in which a logic zero signal is generated at its output, indicating the absence of a fire. The generator 20 generates at its outputs voltage pulses, which are supplied to the first 1 and second 2 sensors. In the first sensor 1, the pulse is amplified in the amplifier 7 and leads to the emission of the light pulse by the converter 8 into the optical camera in the infrared frequency range. If there are no particles of smoke in the chamber, reflected light does not enter the photodetector 9, and the amplitude of the signal U _C2 (Fig. 4) at the output of the amplifier 10 is small. In this case, the second driver of the reference voltage 14 generates a set maximum threshold voltage U _P3 (Fig. 5) supplied to the input of the comparator 16.

The voltage pulse from the generator 20 opens the amplifier 12, from the output of which a normalized signal corresponding to the normal ambient temperature is fed to the input of the comparator 16 U _С4 (Fig. 5) and the input of the second driver of the reference voltage 13. At normal ambient temperature, the driver 13 forms the set the maximum threshold voltage U _P1 (figure 4) supplied to the input of the comparator 15.

In the absence of a fire, the signals coming from the outputs of the first 1 and second 2 sensors to the corresponding inputs of the comparators 15, 16 have an amplitude much smaller than the threshold voltages supplied from the outputs of the voltage reference drivers 13, 14. Therefore, the outputs of the comparators 15, 16 are constantly there are logical zero signals arriving at the corresponding inputs of the OR gate 17. As a result, a logical zero signal is generated at the output of the OR gate 17, which, upon entering the first input of the counter 19, blocks for counting pulses of the generator 20. The generated while the output signal of the counter 19, a logic zero results in the formation unit 6 notification "Norm" in which the LED 22 is not lit, as included in the trail of the fire alarm electronic switch 21 is closed.

In a fire with only one factor, for example smoke during cotton smoldering, the appearance of smoke particles in the optical chamber of the first sensor 1 will cause an increase in the signal at the output of amplifier 10 (curve U _C1 in FIG. 4). Since the temperature of the medium at the detector installation site does not practically change, the threshold voltage of the comparator 15 supplied from the former 13 remains at its maximum (curve U _P1 in Fig. 4). After reaching the threshold value at the time t _{2 by the} voltage U _C1, the output of the comparator 15 appears pulses of a logical unit, which are fed to the input of the logical element "OR" 17 and cause the appearance of pulses of a logical unit at its output. After the accumulation of a certain number of these pulses by the counter 19 for a certain time, which constitutes a delay in operation, a logic unit signal appears at the output of the counter 19, which is fed to the input of block 6 and causes the formation of a Fire warning. In this case, the light indicator turns on in the continuous glow mode, the electronic key opens and closes the line of the fire alarm loop. After decreasing the smoke concentration, the pulses of the logical unit from the output of the "OR" element 17 cease, and after a certain time the detector switches back to standby mode.

In a fire with the presence of heat only, for example, during the combustion of alcohol, an increase in temperature will cause an increase in the signal at the output of amplifier 12 (curve U _C3 in FIG. 5). Since there is virtually no smoke generated, the threshold voltage of the comparator 16 supplied from the former 14 remains at its maximum (curve U _P3 in FIG. 5). After reaching the threshold value at the time t _{4 by the} voltage U _C3 , pulses of a logical unit appear at the output of the comparator 16, which pass through the OR gate 17 and are accumulated by the counter 19, which causes the detector to operate similarly to the one described above.

The real, almost most common fire associated with the burning of various materials, for example cellulose-containing, is accompanied by both the formation of smoke and an increase in temperature. In this case, the voltage at the inputs of the comparator 15 will correspond to the curves U _P2 and U _C1 in figure 4, and the voltage at the inputs of the comparator 16 will correspond to the curves U _P4 and U _C3 in figure 5. Depending on the nature of the combustible load and the fire characteristics, the control signal can reach a threshold value either at the first 15 or at the second 16 comparator. However, in any case, since t ₁ <t ₂ and t ₃ <t ₄ in the inventive detector, a significant reduction in the time of detection of a real fire is achieved.

Thus, in the inventive combined fire detector provides increased reliability of fire detection at its early stage of development.

Improving the reliability of detection in the inventive detector is ensured by the fact that lowering the thresholds of the corresponding detection channel (temperature increase or smoke) is associated with an increase in the probability of a fire hazard occurring when a related factor (smoke or temperature) occurs.

For example, in the particular case of a simple form of the law of probability distribution of a fire hazard situation — uniform, the following dependence of threshold changes by threshold voltage generators 13, 14 can be used.

For shaper 13:

U _П2 = U _П1 - (U _П1 -U _С2 ) P ₁ (U _С3 ) = U _П1 - (U _П1 -U _С2 ) U _С3 / U _П3 .

For shaper 14:

U _P4 = U _P3 - (U _P3 -U _C1 ) P ₂ (U _C1 ) = U _P3 - (U _P3 -U _C1 ) U _C1 / U _P1 ,

where P ₁ (U _С3 ) is the probability of a fire hazard when the temperature rises above normal;

P ₂ (U _C1 ) - the probability of a fire hazard when smoke increases above normal;

Another dependence of the threshold change associated with another, more preferable, law of distribution of the probability of a fire hazard situation can be used. However, it is mandatory to reduce the threshold value of one controlled factor while increasing the intensity of another related factor.

The execution of the temperature converter 11 in the temperature sensor 2 can be performed according to a scheme in which the output signal will be proportional not only to the maximum ambient temperature, but also to the rate of its change (for example, similarly to the IP 101-2 detector [6]). In this case, the thermal detection channel will be maximally differential, which will further increase the reliability of fire detection by the claimed combined fire detector.

Information sources

1. UK patent No. 2169734 A, cl. IPC G 08 B 17/00, 1986.

2. US patent No. 6195011, CL. IPC G 08 B 17/10, 2001.

3. RF patent No. 2110093. Thermal fire detector with frequency filtering, class IPC G 08 B 17/06, 1998.

4. Mathematical Encyclopedic Dictionary / Ch. ed. Yu.V. Prokhorov - M .: Sov. Encyclopedia, 1988 .-- 847 p. (p. 266).

5. Sharovar F.I. Principles of building devices and systems for automatic fire alarms. - M.: Stroyizdat, 1983 .-- 335 s.

6. A.N. Automatic fire detectors: M .: - Research Center "Protection" VNIIPO Ministry of Internal Affairs of Russia, 1997. - 51 p.

7. Optical smoke smoke detector IP212-5M1 (DIP-3M1) Passport PS 951856-89. - Obninsk, Kaluga Region .: JSC Instrument Plant "Signal", 1996. - 16 p.

Claims (4)

1. A combined fire detector containing a smoke sensor, a temperature sensor and a signal processing unit, the first output of which is connected to a smoke sensor, and the second output of the signal processing unit is connected to the input of the temperature sensor, and an alarm notification generator, characterized in that the unit is introduced into it the voltage reference and the comparator unit, the smoke detector output is connected to the first input of the voltage reference unit and the first input of the comparator unit, the temperature sensor output Ura is connected to the second input of the reference voltage generating unit and the second input of the comparator unit, the output of which is connected to the input of the signal processing unit, the third output of which is connected to the input of the alarm notification generator, the output of which is the signal output of the detector, and the third and fourth inputs of the comparator unit are connected, respectively with the first and second outputs of the block forming the reference voltage. 2. The combined fire detector according to claim 1, characterized in that the reference voltage generating unit comprises first and second voltage reference drivers, the first input of the voltage reference forming unit is the input of the second reference voltage driver, the output of which is the second output of the voltage reference forming unit, the second the input of the reference voltage generating unit is the input of the first reference voltage driver, the output of which is the first output of the reference voltage forming unit Costumed. 3. The combined fire detector according to claim 1, characterized in that the comparator unit contains a first comparator, a second comparator and an OR logic element, the outputs of the comparators are connected to the inputs of the OR logical element, the output of which is the output of the comparator unit, the first and third inputs of the comparator unit the inputs of the first comparator, the second and fourth inputs of the block of comparators are the inputs of the second comparator. 4. The combined fire detector according to claim 1, characterized in that the signal processing unit comprises a setting pulse generator, a counter and a pulse generator, the first input of the counter is an input of a signal processing unit, and its output is a third output of a signal processing unit, the output of a setting pulse generator connected to the second input of the counter, the first output of the pulse generator is connected to the third input of the counter, and the other two outputs of the pulse generator are respectively the first and second outputs of the processing unit and signals.

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