JP3015488B2 - Compensated heat detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compensation type heat sensor having a constant temperature function and a differential function.

[0002]

2. Description of the Related Art Conventionally, as a compensation type heat sensor of this type, for example, a structure shown in FIG. 5 is known, and a semiconductor thermistor element whose resistance value changes according to a temperature change is used. A constant temperature function that issues an alarm when the temperature in the monitoring area reaches a preset reference temperature, and detects and issues a case where the temperature in the monitoring area suddenly rises above a predetermined temperature rise rate. It has both functions of operating function to report.

More specifically, the configuration of the compensation type heat sensor will be described with reference to FIG. 5. A positive connection terminal P1 and a negative connection terminal P2 extend from a receiver (not shown) installed in a central monitoring room or the like. The power supply is supplied from the receiver via the transmission line, and the fire alarm is returned from the detector side. Reference numeral 1 denotes a thermistor element having a negative temperature characteristic in which the resistance value decreases as the temperature rises. Reference numeral 2 denotes a constant-value resistor. Have been.

[0004] Reference numeral 4 denotes a thermistor element having a negative temperature characteristic whose resistance value decreases as the temperature rises. Reference numeral 5 denotes a resistor having a constant value.
Supplied to the inverting input contact of Reference numerals 6 and 7 denote voltage dividing resistors which apply a reference voltage VR1 generated at the connection contact to the inverting input contact of the comparator 8. The voltage VC2 is applied to the non-inverting input contact of the comparator 8.

Reference numerals 9 and 10 denote diodes connected to the output contacts of the comparators 3 and 8, respectively. Signals generated at the commonly connected cathode contacts are connected to resistors 11 and 12 and a capacitor 13 respectively.
Is supplied to the gate contact of the thyristor element 14 via the. Here, assuming that the thermal time constant of the thermistor element 1 is TH1 and the thermal time constant of the thermistor element 4 is TH4, these thermistor elements 1 and 4 both have a resistance value at room temperature and a resistance change rate due to temperature rise. Those having the same thermal time constant of TH1 <TH4 are used.

If the resistance value of the resistor 2 is R2 and the resistance value of the resistor 5 is R5, the relationship of R2 <R5 is established. In a normal temperature state where the temperature change in the monitoring area is small, the voltage VC2 at the inverting input contact of the comparator 3 is designed to be higher than the voltage VC1 at the non-inverting input contact.
In the normal temperature state, the output of the comparator 3 is set to the "L" level.

Further, the voltages VC1 and VR1 applied to the respective input contacts of the comparator 8 also become "L" at normal temperature.
The values of the resistors 6 and 7 are set so as to be at the level. Next, the operation of the heat sensor will be described. Note that the resistance values of the thermistor elements 1 and 4 will be described as r1 and r4.
First, when the temperature in the monitoring area rises rapidly as in the case of an initial fire, the thermal time constant of the thermistor elements 1 and 4 becomes TH1 <
Because of the relationship of TH4, the resistance value r1 of the thermistor element 1 rapidly decreases, and the reduction of the resistance value r4 is delayed. Therefore, the voltage VC1 rises rapidly and the voltage VC1
And the voltage VC2 becomes VC1> VC2, the output signal of the comparator 3 is inverted from "L" to "H", and the thyristor element 1
Trigger 4 to turn on. Then, the occurrence of a fire is confirmed by a receiver (not shown) detecting that the impedance between the connection contacts P1 and P2 has decreased due to the ON state.

As described above, the differential function is obtained by applying the thermistor elements 1 and 4 having the same resistance value and the same resistance change rate and different thermal time constants. On the other hand, in the case of the constant temperature function, that is, when the temperature rise in the monitoring area is not rapid but gradually reaches a predetermined high temperature corresponding to a fire, the resistance values of the thermistor elements 1 and 4 with respect to the resistance values r1 and r4. Since the decrease is equal, the voltages VC1 and VC2 rise equally, and the output signal of the comparator 3 always remains at "L" level.

On the other hand, while the voltage VC1 applied to the non-inverting input contact of the comparator 8 gradually increases, the reference voltage VR1 remains at a constant value. VC1> VR1 at the point of time when the
Is inverted from "L" to "H" level, triggering the thyristor element 14 to turn it on to notify the receiver of the fire occurrence.

That is, a constant temperature function is obtained by issuing an alarm when the voltage VC1 that changes in proportion to a predetermined temperature rise exceeds the reference voltage VR1.

[0011]

However, since two thermistor elements having different thermal time constants are used,
There was a problem that the structure of the sensor became complicated. That is, in order to make the thermal time constant different, the temperature of the monitoring area is directly affected by providing the thermistor element 1 outside the sensor, and one thermistor element 4 is installed inside the sensor. This is achieved by indirectly affecting the temperature of the monitored area. Therefore, the installation position and the like of the thermistor element depend on the shape and structure of the sensor, and the wiring and the like are complicated. Further, if the installation position of the thermistor element is different, the thermal time constant changes,
There was a problem that optimal design became difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and has a single temperature detecting element such as a thermistor element, and a compensation function for obtaining a differential function and a constant temperature function based on a change in the temperature detecting element. It is an object of the present invention to provide a thermal sensor.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for detecting the presence or absence of a fire based on a change in the resistance of a heat detecting element having a characteristic that the resistance decreases with an increase in temperature. The target is a compensation type heat sensor to be detected. Then, a current proportional to the resistance value of the heat detecting element is generated by the current converting means, and a voltage drop is caused in the first resistor by the generated current from the current converting means. The current causes a voltage drop in the time constant circuit formed by the capacitive element and the second resistor, and
When the voltage drop of the resistor exceeds the voltage drop of the time constant circuit, an output signal indicating the occurrence of a fire is generated in the first comparing means, and the voltage drop of the first resistor is set to a predetermined reference voltage. An output signal indicating the occurrence of a fire is generated by the second comparing means when it exceeds the threshold value. If no fire has occurred, the voltage drop by the second resistor is larger than the voltage drop by the first resistor. Further, a predetermined relationship where the reference voltage is larger than the voltage drop due to the second resistor is set.

[0014]

According to the present invention having such a configuration, when the temperature rises rapidly, the resistance value of the heat detecting element decreases and the voltage drop of the first resistor causes the voltage drop. When the difference between the voltage drops of the constant circuit is enlarged and the first comparing means exhibits a differential function of detecting a fire, and the temperature rises slowly, the voltage drop of the first resistor and the time constant There is almost no difference in the voltage drop of the circuit, and when the voltage drop of the first resistor exceeds the reference voltage, the second comparing means exhibits a constant temperature function of detecting a fire. Both functions can be realized by one heat detecting element.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. First, the circuit configuration will be described with reference to FIG. In FIG. 1, P1 and P2 are connection terminals connected to a transmission line extending from a receiver (not shown), and a constant voltage circuit such as a three-terminal regulator connected between these connection terminals P1 and P2. 15 forms a constant power supply voltage VDD, and the power supply voltage VDD activates a circuit for detecting the next fire.

Reference numerals 16, 17, and 18 denote PNP transistors whose base contacts are connected in common, and their emitter contacts are connected to the positive side of the power supply voltage VDD via resistors 19, 20, and 21, respectively. The transistor 16 has a base contact and a collector contact commonly connected, and this connection contact is connected via the thermistor element 22 to the negative side of the power supply voltage VDD (connection contact P2). The collector contact of the transistor 17 is connected to the connection contact P2 via the resistor 23, and the collector contact of the transistor 18 is connected to the connection contact P2 via the resistor 24.

That is, these transistors 16-18,
The circuit including the thermistor element 22 and the resistors 19 to 21, 23, and 24 forms a so-called current mirror circuit, and includes the transistor 16, the resistor 19, and the thermistor element 2
The current proportional to the current determined by the internal resistance of the second element 2 flows through the resistors 23 and 24. Further, a capacitance element 25 and a resistor 26 connected in series with each other are connected between the power supply VDD,
The connection contact q1 is connected to the base contact of the NPN transistor 28 via the resistor 27, and the collector contact of the transistor 28 is connected to the collector contact q of the PNP transistor 17.
2 and the emitter contact is connected to the connection terminal P2.

Numeral 30 denotes a comparator whose non-inverting input contact is connected to the contact q2 and whose inverting input contact is PN.
It is connected to the collector contact q3 of the P transistor 21. Further, a capacitive element 31 in parallel with the resistor 24 is connected to the inverting input contact. 32 is a comparator, which is a power supply voltage V
The reference voltage generated at the connection contact q4 is supplied to the inverting input contact by the voltage dividing resistors 33 and 34 connected between the DD,
The voltage of the contact q2 is supplied to the non-inverting input contact.

Reference numerals 35 and 36 denote diodes connected to predetermined output contacts of the comparators 30 and 32. A commonly connected cathode contact is connected to a thyristor element via a smoothing circuit composed of resistors 37 and 38 and a capacitance element 39. 40 gate contacts. The anode contact of the thyristor element 40 is connected to the connection terminal P1, and the cathode contact is connected to the connection contact P1.
2 connected.

Here, the condition of each circuit constant is as follows:
20 and 21 have the same resistance, and the PNP transistor 1
6, 17, 18 are equal, and the resistance value of the resistor 23 is R
23 and the resistance of the resistor 24 are R24, then R23 <R
24 are set. Therefore, the respective current values flowing through the thermistor element 22 and the resistors 23 and 24 are equal,
The voltage Vq2 of the contact q2 and the voltage Vq3 of the contact q3 are Vq2 <V
It is set to q3.

Next, the operation of the embodiment having such a configuration will be described. still. When the heat sensor is connected to the transmission line, the capacitance element 25, the resistors 26, 27, and the transistor 28 are not charged with electric charge. Therefore, the potential of Vq3 is low, and Vq2> Vq3. Is an "H" level, which causes a fire alarm. In order to prevent this, the circuit sets Vq2 = 0 during the time until the capacitive element 31 is charged.

First, the case of the differential function will be described with reference to FIG. At room temperature where no fire occurs, the contacts q2 and q
3 are in a relationship of Vq2 <Vq3, and the contacts q2 and q
4 have a relationship of Vq4> Vq2, the comparator 30,
The 32 output signals Q30 and Q32 are both at "L" level. Then, as shown in FIG. 2A, when the temperature of the monitored area rises sharply, the resistance value of the thermistor 22 rapidly decreases following the temperature change as shown in FIG. 2B.

Therefore, the collector currents of the PNP transistors 16, 17, and 18 constituting the current mirror circuit increase equally, and the voltage Vq2 of the contact q2 also increases rapidly in proportion to the increase of the current. On the other hand, the collector current of the transistor 18 similarly increases, but the voltage Vq3 of the contact q3 slowly increases depending on the time constant determined by the capacitance value of the capacitive element 31 and the charging current value flowing through it. As a result, when the temperature rises sharply, the potential difference between the voltage Vq3 and the voltage Vq2 expands, and when Vq2> Vq3, as shown at time t1 in FIG. 2C, as shown in FIG. 2D. The output signal Q30 of the comparator 30 is inverted from "L" to "H" level to trigger the thyristor element 40, and at the same time, as shown in FIG.
As shown in (E), the voltage between the connection terminals P1 and P2 decreases. As a result, the occurrence of a fire can be reported to the receiver.

Even if the voltage Vq2 rises due to such a rapid temperature rise, if the actual temperature in the monitoring area does not reach the high temperature state at which it is determined that a fire has occurred, the voltage Vq2 will The reference voltage Vq4 set at the inverting input contact
, Since these voltages Vq4 and Vq2 are set in advance, the output signal Q32 of the comparator 32 is always at "L" level.

As described above, the differential function is obtained by one thermistor element 22 by applying the integrating function of the resistor 24 and the capacitive element 31. Next, the case of the constant temperature function will be described with reference to FIG. Incidentally, at normal temperature where no fire occurs, the voltages of the contacts q2 and q3 have a relationship of Vq2 <Vq3,
Further, since the voltages at the contacts q2 and q4 have a relationship of Vq4> Vq2, the output signals Q30 and Q32 of the comparators 30 and 32 are both at the "L" level.

When the temperature of the monitored area rises slowly as shown in FIG. 3A, the resistance of the thermistor 22 follows the temperature change as shown in FIG. 2B. Decrease slowly. Therefore, the collector currents of the PNP transistors 16, 17, and 18 constituting the current mirror circuit gradually increase, and the voltages Vq2 and Vq3 of the contacts q2 and q3 gradually increase in proportion to the increase of the current. .

Here, if the collector currents of the PNP transistors 17 and 18 increase slowly and the rate of increase is slower than the time constant determined by the capacitance value of the capacitive element 31 and the charging current flowing therethrough, the voltages Vq2 and Vq3 Rise changes are approximately equal. As a result, the voltage does not reverse as in the case of the differential function shown in FIG. 2C, the relationship of Vq3> Vq2 is always maintained, and the output signal Q30 of the comparator 30 has the "L" level. Will remain.

When the temperature further rises and reaches a preset dangerous temperature (for example, 60 ° C.), FIG.
As shown at time t2, the relationship between the voltage Vq2 and the reference voltage Vq4 is Vq2> Vq4, and as shown in FIG.
The output signal Q32 of the comparator 32 inverts from "L" to "H" level to trigger the thyristor element 40, and as shown in FIG. Notify the side of the fire.

As described above, a constant temperature function for detecting that the temperature has reached the dangerous temperature when the temperature gradually rises is obtained. In this embodiment, only one thermistor element is used, and the differential function and the constant temperature function can be obtained only by setting the time constant of the integrating circuit using a simple resistor and a capacitor, so that the circuit is simplified and adjusted. Can also be easier.

Next, another embodiment will be described with reference to FIG.
In FIG. 4, the same or corresponding parts as those in FIG. 1 are indicated by the same reference numerals. This embodiment uses an NPN transistor 4 instead of a large-scale comparator having a built-in differential pair.
1, 42 have the same comparison function.

That is, in FIG. 4, the base contact of the transistor 41 is connected to the contact q2, the emitter contact is connected to the contact q3, and the collector contact is connected to the diode 36. On the other hand, the base contact of the transistor 42 is connected to the contact q3, the emitter contact is connected to the contact q4, and the collector contact is connected to the diode 35. The common anode contacts of the diodes 35 and 36 are resistors 43 and 4
PNP transistor 4 via a bias circuit comprising
5, the emitter contact of the transistor 45 is connected to the connection terminal P1, and the collector contact is connected to the resistor 3
It is connected to the gate contact of the thyristor element 40 via a smoothing circuit composed of the elements 7, 38 and the capacitance element 39.

When comparing the transistors 41 and 42 with the comparators 30 and 32 shown in FIG. 1, the non-inverting input contact and the inverting input contact of the comparator 30 correspond to the base contact and the emitter contact of the transistor 41, respectively. 32 non-inverting input contacts and inverting input contacts correspond to the base contact and the emitter contact of the transistor 42. And each transistor 4
Signals Q30 and Q32 indicating a fire are output when the base-emitters 1, 42 are biased in the forward direction. The output signals Q30 and Q32 of this circuit are output from the comparator 3 shown in FIG.
Since the output signals of 0 and 32 have the opposite logic, these signals are further inverted by the PNP transistor 45 and then supplied to the thyristor element 40, whereby the function equivalent to the circuit of FIG. ing.

When the temperature rises sharply, the transistor 41 is biased in the forward direction, so that it exhibits a differential function.
Is biased in the forward direction, whereby a constant temperature function is exhibited.

[0034]

As described above, according to the present invention, when the temperature rises sharply, as the resistance value of the heat detecting element decreases, the voltage drop of the first resistor decreases. When the difference between the voltage drops of the time constant circuit is enlarged and the first comparing means exhibits a fire detecting differential function and the temperature rises slowly, the voltage drop of the first resistor and the time There is almost no difference in the voltage drop of the constant circuit, and when the voltage drop of the first resistor exceeds the reference voltage, the second comparing means performs a constant temperature function of detecting a fire. Both functions can be realized by one heat detecting element.

As described above, since both the differential function and the constant temperature function can be obtained by one heat detecting element, it is easy to set circuit constants and the like for an optimum design, and to have a small and simple structure. Can be easily realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a characteristic curve diagram for explaining the operation of the differential function of the embodiment.

FIG. 3 is a characteristic curve diagram for explaining the operation of the constant temperature function of the embodiment.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing a circuit configuration of a conventional example.

[Description of References] P1, P2; connection terminals 16, 17, 18, 45; PNP transistors 19 to 21, 23, 24, 26, 27, 33, 34; resistor 22; thermistors 25, 31, 39; , 32; comparators 35, 36; diode 40; thyristors 41, 42;

Claims (1)

(57) [Claims] 1. A compensation type heat sensor for detecting the presence or absence of a fire based on a change in the resistance of a heat detection element having a characteristic that the resistance decreases with an increase in temperature. A current converting means for generating a proportional current, a first resistor for generating a voltage drop when the generated current is supplied from the current converting means, and a current generating means for supplying the generated current from the current converting means and connected in parallel A second resistor that causes a voltage drop depending on a time constant caused by the first capacitive element and the first resistor.
First comparing means for generating an output signal indicating a fire when the voltage drop of the resistor exceeds the voltage drop of the second resistor;
A second comparing means for generating an output signal indicating the occurrence of a fire when the voltage drop of the first resistor exceeds a preset reference voltage;
A compensation type heat sensor, wherein a predetermined relationship is set such that a voltage drop due to the second resistor is larger than a voltage drop due to the first resistor, and a reference voltage is larger than a voltage drop due to the second resistor.