RU2275687C2 - Thermal fire alarm - Google Patents

Abstract

FIELD: fire signaling equipment engineering, in particular, engineering of thermal fire alarms, possible use for detecting fire by increase in temperature of environment in place where alarm is mounted.

SUBSTANCE: fire alarm uses three thermo-sensitive elements, made on thermo-resistors, which have varying constant of time needed for change for resistance during change of temperature (thermal inertia).

EFFECT: stabilization of inertia process, achieved due to adaptation of activation temperature during slow change of environment temperature in absence of fire.

4 dwg

Description

The invention relates to a fire alarm technique.

Known thermal fire detector IP 105-2 / 1 (ITM) [1], containing a heat-sensitive element in the form of a system of ring permanent magnets having a Curie point near 70 ° C, with metal heat sinks installed between them, and a fire alert generator in the form sealed magnetically controlled electrical contact.

During operation, the detector is connected in series to a two-wire electrical circuit (alarm loop), its normally closed state indicates the absence of a fire at the controlled object. The ambient temperature, equal to the Curie point, is the threshold temperature of the heat detector, at which a permanently closed magnetically controlled electrical contact opens.

The disadvantage of the heat detector [1] is the large inertia of the response caused by the significant thermal inertia of its heat-sensitive element. At a slew rate of 0.2 ° C / min or less, the threshold temperature is maximum and practically unchanged. At a higher rate of temperature rise (more than 1 ° C / min), the response time (inertia) somewhat decreases, but still remains significant. For example, for a prototype detector, when the temperature changes abruptly, it amounts to 120 s according to fire safety standards [2], and at an ambient temperature rise rate of 1 ° C / min for detectors of this type it can increase to 2420 s.

In addition, the disadvantage of this detector is the low stability of its inertia at various initial (average) ambient temperatures. During operation, the average temperature at the installation site of the detector can slowly vary to a large extent. For example, it is possible to slowly decrease the temperature relatively relatively normal (for example, in the winter at night or when the heating is turned off), which leads to a significant increase in the difference between the initial (average) temperature of the medium and the threshold temperature. This significantly increases the detector response time in case of fire.

It is also possible to increase the initial (average) ambient temperature and approach the detector threshold on a hot summer day, for example, under the influence of sunlight, during the operation of heating plants, etc. This can lead to false alarms of the detector with relatively short-term fluctuations in the temperature of the medium at the installation site in the absence of thermal effects from a fire.

That is why the regulatory literature does not recommend the use of maximum heat detectors in facilities where a significant decrease in temperature at the detector installation site [3] or its heating under the influence of solar and other thermal radiation is possible [4].

Partially indicated disadvantages are eliminated in the thermal maximum differential detector IP 101-2 [5], which is the closest to the claimed device. The structural diagram of the detector prototype is presented in figure 1.

The detector contains the first 1 and second 2 thermosensitive elements, a voltage reference driver 3, a voltage comparator 4 and a fire alert driver 5. The outputs of the first 1 and second 2 temperature sensors are connected to the first input of the voltage comparator 4, the output of the voltage reference driver 3 is connected to the second input voltage comparator 4, the output of which is connected to the shaper of the fire notification 5. The shaper of the fire notification 5 contains a memory unit 6, the first output of which through the electronic key 7 The key to the indicator light 9, and a second output connected to the input interface unit 8. The entrance of the storage unit 6 is an input driver notification of a fire 5, and outputs the block coupling 8 is the output of a fire notification 5.

The first 1 thermosensitive element is made on the thermistor 10, the second 2 thermosensitive element is made on the thermistor 11 and resistor 12 connected in series, the voltage shaper 3 is made in the form of a voltage divider on the resistors 13-15 connected in series.

The first heat-sensitive element 1, made on the thermistor 10, equipped with a heat receiver and placed in direct contact with the environment, due to the various heat transfer conditions created, has a heating time constant less than the same second heat-sensitive element 2 on the thermistor 11, but located inside the housing. During operation, the detector is connected via the interface unit to the alarm loop of the fire alarm control panel. In standby mode, the current consumption of the detector from the alarm loop is minimal and is determined by the sum of the conductivities of the voltage dividers of blocks 1-3. With a slow increase in ambient temperature with a time constant that is much larger than the heating time constant of the thermistors 10 and 11 of the first 1 and second 2 heat-sensitive 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 input changes due to an increase in voltage at the resistor 12. At a temperature of + 60 ° C, the comparator opens, forming a control signal to the input of the memory unit 6. The memory unit 6 opens, the current flowing through it increases sharply, including using the electronic key 7, the indicator light 9 in the continuous mode of illumination and leading to increased current consumption of the detector from the alarm loop. The detector is triggered as maximum, indicating that the ambient temperature exceeds the set threshold value. The detector temperature is set at the factory using the tuning resistor 14.

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 increase in voltage at the first measuring input of the comparator. After reaching the value of this voltage of a constant threshold value, the comparator 4 opens, leading to the formation of a fire notification unit 5.

Thus, in the prototype device, a fire notification for an increased rate of rise in the temperature of the medium is formed at a lower temperature than for a slow change in the temperature of the medium, and, accordingly, in less time. As thermosensitive elements, small-sized semiconductor thermistors with a small thermal inertia are used.

In such detectors, the value of the temperature rise rate at which an effective decrease in the response time is observed is usually set to at least 6-8 ° C / min [4, 5]. Therefore, in case of fires for which the temperature rise rate is less important, the detector works only as the maximum with the insufficient inertia stability noted above with deviations of the operating temperature of the medium.

The problem to be solved in the inventive heat detector is the stabilization of its inertia, achieved by adapting the response temperature with a slow change in ambient temperature in the absence of a fire. For this, an additional dependence of the response threshold on the value of the average (initial) ambient temperature is introduced.

Changing the response threshold under the influence of external factors is known and is used in devices for alarming, for example, in the ultrasonic security detector "Echo-3" [6]. In this device, when exposed to interference, a proportional change in the threshold voltage occurs. A slow change in the voltage at the input of the threshold block caused by the reflection of ultrasound from a directed upward turbulent air flow, for example from a heating battery, does not lead to a false alarm. Thus, here, in contrast to the inventive detector, the problem of increasing noise immunity is solved, while the adaptation time is much shorter and amounts to seconds. In addition, the signal supplied to the input of the threshold block can have both a positive and a negative sign, therefore, it is necessary to use two thresholds in the device [6]. In the inventive detector, another task is solved - stabilization of inertia, the time constant of the threshold change is hours, and adaptation is carried out from a separate channel for converting the primary information - an additionally introduced heat-sensitive element. Thus, the novelty of the proposed technical solution in comparison with the device [6] is significant.

In the claimed device, the task is solved by the fact that in the well-known thermal fire detector [5], containing the first and second heat-sensitive elements, outputs connected to the first input of the voltage comparator, the output of which is connected to the driver of the fire notification, a third heat-sensitive element and a controlled driver are introduced voltage. The third heat-sensitive element is connected to the first input of the controlled voltage driver, the output of which is connected to the second input of the voltage comparator.

In the inventive detector, all known elements can be performed identically to the prototype device [5]. The controlled voltage driver can also be identical to the prototype device [5] and have an additional control input connected to one of the resistors. The third heat-sensitive element can be performed on a thermistor. A variant of the circuit implementation of the newly introduced blocks of the claimed device is presented in figure 3.

Figure 2 shows a diagram of the inventive thermal fire detector.

The device contains the first 1, second 2 and third 3 thermosensitive elements, a controlled voltage driver 4, a voltage comparator 5 and a fire alert generator 6. The outputs of the first 1 and second 2 temperature sensors are connected to the first input of the voltage comparator 4, the output of the third thermosensitive element 3 connected to the input of the controlled driver of the reference voltage 4, the output of which is connected to the second input of the voltage comparator 5. The output of the voltage comparator 4 is connected to the driver and light situations a fire 6.

Thermal detector operates as follows.

Three thermosensitive elements made on thermistors, due to the different heat transfer conditions created, have different time constant of resistance change with temperature change (thermal inertia). The first heat-sensitive element 1 has a minimum thermal inertia. The second 2 has a thermal inertia greater than the first. The third heat-sensitive element 3 has a thermal inertia much more than the first 1 and second 2 heat-sensitive elements. Illustrating this feature, the graphs of changes in the voltages supplied to the comparator inputs when the temperature of the controlled medium changes at different speeds are shown in Fig. 4.

During operation, the detector is connected to the alarm loop of the control panel. When a slow, less than 0.2 ° C / min, increase in ambient temperature (Fig. 4a), as a rule, not associated with a fire, the resistance of the thermistors of the first 1, second 2 and third 3 heat-sensitive elements are proportionally reduced. At the same time, the voltage U _in1 at the first measuring input of the comparator 5 changes insignificantly with respect to the voltage at its second input U _in2 , so that the voltage difference is sufficient to provide the required level of noise immunity during fluctuations of thermal noise and other noise. The resistance parameters of the thermosensitive elements are selected in such a way that with a further slow increase in the temperature of the medium (with a possible very slow development of the fire), the voltage U _in1 at the first input of the comparator 5 (at t _cf1 ) reaches and begins to exceed the threshold voltage at its second input U _in2 . At the same time, a control signal appears at the output of the comparator 5, causing the unit 6 to form a fire notification signal in the loop.

With a more rapid increase in room temperature (Fig. 4b) of about 1-2 ° C / min, which indicates the likely occurrence of a fire, the voltage at the second input of the comparator 5 does not increase significantly. Therefore, the voltage at the first input of the comparator 5 at a lower temperature than t _srab (in Fig. 4a) reaches the voltage at its second input (t _srb1 <t _srb2 <t _srb ). In this case, the response threshold U _in2 will be the smaller, the lower the initial temperature, with which a relatively rapid increase in the temperature of the medium _begins (U _in2 (t _work.min ) <U _in2 (t _work )). Thus, the adaptation of the threshold voltage at the second input of the comparator reduces the time of fire detection at the initial low temperature of the medium, bringing this time closer to the time of detection at a high initial temperature in the range of operating temperatures.

With a rapid increase in temperature in the room (Fig. 4 c), at a speed of more than 5 ° C / min, which indicates the appearance of a rapidly developing fire, the voltage U _in2 at the second input of the comparator 5 practically does not change. The voltage U _in1 at the first input of the comparator 5 increases relatively more rapidly than in the previous case _due to the _low-varying resistance of the second heat-sensitive element (due to its thermal inertia much more than the first heat-sensitive element). Therefore, the voltage U _in1 at the first input of the comparator 5 will reach the voltage U _in2 at its second input at a lower temperature than in the previously considered case (t _srb3 <t _srb1 ; t _cpab4 <t _srb ). However, in this case, if the rapid temperature increase associated with the fire began at a low temperature (t _work.min <t _work ), then due to the lower position of the threshold voltage (U _in2 (t _work.min ) <U _in2 (t _slave )) the operation of the inventive detector will occur much earlier than the detector - analog and prototype. Thus, the adaptation of the threshold voltage at the second input of the comparator 5 provides, in this case, a decrease in the time of fire detection relative to the detectors - analogue and prototype. In this case, the inertia of the heat detector will practically not depend on the initial temperature (with which the fire started) in the entire range of operating temperatures.

Thus, in the inventive detector, stabilization of inertia is achieved when the ambient temperature changes within a significant range.

In the process of development, a sample of the inventive heat detector was manufactured. Tests have confirmed its performance in accordance with the above description.

INFORMATION SOURCES

1. USSR author's certificate No. 1244686, MKI G 08 B 17/06, 1984.

2. NPB 85-2000 Thermal fire detectors. Technical requirements for fire safety. Test methods.

3. NPB 88-2001 Fire extinguishing and alarm systems. Norms and design rules.

4. M. Edams. A.N. Chlenov Guidelines for the use of intelligent fire alarm systems. - M.: System Sensor Fire Detector, 2003. - 55 p.

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

6. Detector security surface ultrasonic ИО308-1 "Эох-3". The average repair manual Dv 3.836.013 PC, 1992. - 60 p.

Claims (1)

Thermal fire detector containing the first and second thermosensitive elements, outputs connected to the first input of the voltage comparator, the output of which is connected to the fire alarm generator, characterized in that a third thermosensitive element and a controlled voltage driver are inserted into it, the third thermosensitive element is connected to the input controlled shaper of the reference voltage, the output of which is connected to the second input of the voltage comparator, the first thermosensitive ement has minimal thermal inertia and the second has a thermal inertia greater than the first, the third temperature sensing element has a thermal inertia greater than the second temperature sensing element.

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