JPH10334360A - Digital heat sensor and digital heat sensor for house - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-reliability digital heat sensor, with which abnormality such as the disconnection or short-circuiting of temperature detection circuit can be always monitored as well by a heat sensor itself, and a high-reliability digital heat sensor four house applying this basic principle. SOLUTION: This sensor is provided with a temperature detection circuit 2 having a thermistor TH as a temperature detecting element, A/D converting means 3 for converting the voltage output of this temperature detection circuit 2 to the temperature measure value of digital signal, discriminating means 4 for discriminating the disconnection alarm or short-circuiting by comparing this temperature measure value with the respective threshold values of disconnection, alarm and short-circuiting, and output circuit 5 for outputting a discriminate signal from this discriminating means 4 to a monitoring line 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital heat sensor having a function of constantly diagnosing and detecting a fault such as a disconnection or a short circuit of a temperature detection circuit, and a digital heat sensor for a house.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing an example of the internal configuration of a conventional heat detector having a temperature detecting circuit. In the heat sensor 100, a resistance element R1 is connected in series to a thermistor RTH having a large resistance value change in response to a change in ambient temperature, and a resistance element R serving as a reference resistance is further connected to this series circuit.
The temperature detection circuit 102 is configured by connecting a series circuit of the R2 and R3 in a bridge shape. The comparator 101 determines a change in the output of the temperature detection circuit 102, and turns on and off the transistor Tr. The fire signal is output to the fire receiver 7 through the monitoring line 6.

Therefore, in such a heat sensor, when a fire occurs, the thermistor RT increases with an increase in ambient temperature.
Since the resistance value of H sharply decreases, the divided output Vi of the resistance element R1 becomes larger than the divided output Vo of the reference resistance element R3, so that the comparator 101 outputs an H level signal. As a result, the transistor Tr is turned on and the monitoring line 6 is short-circuited to the ground level through the transistor Tr and the resistance element R4. The fire receiver 7 detects this state and outputs a fire alarm.

On the other hand, the thermistor RTH is always
The resistance value of the resistor R
1 is the divided output Vo of the reference resistance element R3.
Since it becomes smaller, the comparator 101 outputs an L level signal. As a result, the transistor Tr is turned off, so that the monitoring line 6 is not short-circuited, and the fire receiver does not output a fire alarm. FIG. 9 is a table showing the basic operation of this conventional heat sensor.

[0005]

However, in the above-described heat detector, as can be understood from FIG. 8, the magnitude of the divided output Vi of the resistance element R1 on the thermistor side and the divided output Vo of the reference resistance element R3 is large. Is compared only by the comparator, so that there are the following problems. That is, the thermistor R
If TH is short-circuited or the resistor element R1 is disconnected, the divided output Vi on the thermistor RTH side becomes almost the power supply voltage VDD and the divided output Vo on the reference resistor element side.
Be larger. For this reason, the transistor Tr is turned on in the same manner as in the case of a fire, and an erroneous fire is generated even though no fire has occurred.

If the thermistor RTH is disconnected or a short circuit occurs in the resistance element R1, the thermistor RTH
The divided voltage Vi on the side is almost at the ground level, and is smaller than the divided voltage Vo on the reference resistance element side. Therefore, the transistor Tr is turned off as in the normal state,
In spite of the occurrence of the abnormality, the abnormality is not notified.

[0007] In order to perform such an operation, a conventional heat sensor is required to be periodically inspected by the Fire Service Law or the like. For that purpose, a heat tester, a dryer or a lighter is used. Operation has been confirmed,
It also caused the thermistor to fail. The present invention has been made in view of the above circumstances, and a highly reliable digital heat sensor capable of constantly monitoring an abnormality such as a disconnection or short circuit of a temperature detection circuit by the heat sensor itself. It is an object of the present invention to provide a highly reliable digital heat sensor for a house using the principle.

[0008]

According to a first aspect of the present invention, there is provided a digital heat detector connected to a monitoring line of a fire receiver. A temperature detection circuit having a temperature detection element, an A / D converter for converting a voltage output of the temperature detection circuit into a temperature measurement value of a digital signal; A determination means for comparing the threshold values of the alarm and the short circuit to determine a disconnection, an alarm and a short circuit, and an output circuit for outputting a determination signal from the determination means to the monitoring line.

The digital heat sensor proposed in claim 2 is further provided with alarm display means for displaying an alarm for disconnection, alarm, or short circuit in accordance with the discrimination signal from the discrimination means. The digital heat sensor proposed in claim 3 further comprises an operation check circuit having a test switch according to claim 2, wherein when the test switch is operated, test value data is input to the discriminating means, and the operation is performed. The configuration is such that abnormality can be determined.

In the digital heat sensor proposed in claims 4 and 5, in any one of claims 1 to 3, the temperature detection circuit constitutes a voltage dividing circuit in which a resistance element is connected in series to a thermistor. The temperature detection circuit is configured to extract the divided voltage output of the resistance element, or the temperature detection circuit is configured to form a voltage division circuit in which a resistance element is connected in series to the thermistor, and to extract the divided voltage output of the thermistor.

According to a sixth aspect of the present invention, there is provided a digital heat sensor for a house, which is mounted on a ceiling or a wall in a house for use, and comprises a temperature detecting circuit having a temperature detecting element. A / D conversion means for converting the voltage output of the temperature detection circuit into a temperature measurement value of a digital signal, and comparing the temperature measurement value with respective threshold values of disconnection, alarm, and short-circuit, An alarm, a determination means for determining a short circuit, and a determination signal from the determination means, the disconnection,
An alarm display means for displaying an alarm of an alarm or a short circuit, and a power supply circuit having an insertion plug and converting a commercial power supply to an internal power supply are provided.

A digital heat sensor for a house proposed in claim 7 is further provided with an operation check circuit having a test switch according to claim 6, and when the test switch is operated, a test value is supplied to the discriminating means. It is configured to input data and determine an operation abnormality. The residential digital heat sensor proposed in claim 8 is claim 6,
In 7, the temperature detection circuit constitutes a voltage dividing circuit in which a resistance element is connected in series to a thermistor, and takes out a divided voltage output of the resistance element.

According to a ninth aspect of the present invention, there is provided a digital heat sensor for home use according to the sixth and seventh aspects, wherein the temperature detecting circuit comprises a voltage dividing circuit in which a resistance element is connected in series to a thermistor. To take out the partial pressure output.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the following, embodiments of a digital heat sensor and a residential digital heat sensor according to the present invention will be described. FIG. 1 is a block diagram showing an example of an internal circuit of a digital heat sensor according to the present invention. This digital heat sensor is connected to a monitoring line such as a fire receiver as a fire sensor and constitutes a self-fire alarm system.

The digital heat detector A is connected to a fire receiver 7 through a monitoring line 6 and outputs a temperature detection circuit 2 having a thermistor TH as a temperature detection element and a voltage output of the temperature detection circuit 2. A / D conversion means 3 which converts the temperature into a digital signal and takes it out as a temperature measurement value, and compares this temperature measurement value with the respective threshold values of disconnection, alarm, and short circuit, and determines disconnection, alarm, and short circuit. It comprises a discriminating means 4 and an output circuit 5 for outputting a discrimination signal from the discriminating means to a monitoring line 6. In the figure, the internal circuit excluding the temperature detection circuit 2 is shown as 1. The internal circuit 1 is supplied with an internal power supply VDD.

Here, the output circuit 5 preferably has a function of transmitting a multiplex signal to and from the fire receiver 7. In this case, the fire receiver 7 normally polls the digital heat sensor A in a time-division manner to determine the disconnection or short circuit of the monitoring line 6 and the abnormal operation of the sensor. When an abnormality is determined in step (1), an interrupt signal is sent to the fire receiver 7 to perform necessary processing.

FIG. 2 is a block diagram showing the internal configuration of a digital heat sensor provided with an alarm display means in addition to the basic configuration shown in FIG. Parts corresponding to those in FIG. 1 are denoted by the same reference numerals. The digital heat sensor B further includes an alarm display unit 8 that displays an alarm corresponding to a disconnection, an alarm, or a short circuit based on a determination signal from the determination unit 4.
Abnormalities of disconnection, alarm, and short circuit can be easily determined from outside the sensor. The warning display means 8 may be configured to change the blinking color and blinking form of the LED or the like in accordance with disconnection, alarm, or short circuit abnormality.

FIG. 3 is a block diagram showing a configuration of an internal circuit of the digital heat detector having a test switch so that an operation test can be performed. This digital heat sensor C
Further includes an operation check circuit 9 having a test switch SW. In this operation check circuit 9, the test switch SW
Is operated, the operation abnormality can be determined by inputting the test value data to the determination means 4. Here, as the test value data, a digital signal of the same level or higher than the temperature measurement value output when the temperature detection circuit 2 receives heat when a fire occurs is prepared. The operation abnormality of the internal circuit including the discriminating means 4 constituted by a CPU or the like can be confirmed at any time without performing a heating test for externally heating. In such a digital heat sensor C, the alarm display means 8 is normally selected so as to output the same alarm sound as at the time of a fire alarm when the operation is normal, but when the operation is abnormal. Then, an alarm sound different from the fire alarm may be output.

FIGS. 4A and 4B are circuit diagrams each showing an example of a temperature detection circuit used in the digital heat detector of the present invention. FIG. 4A shows that the thermistor TH as a temperature detecting element is connected to the power supply VDD side, the resistance element R is connected to the ground side, and the divided output of the connection point, that is, the divided output of the resistance element R is represented by A. FIG. 4 (b) shows an example in which the signal is taken out to the / D conversion unit 3, and FIG.
H is connected to the ground side, the resistance element R is connected to the power supply VDD side, and a divided voltage output from the connection point, that is, the thermistor TH
2 shows an example in which the divided voltage output is extracted to the A / D converter 3.

4 (a) and 4 (b) have different output levels at the time of short-circuiting, disconnection, and alarm, so it is necessary to determine the respective thresholds according to the temperature detection circuit employed. . It goes without saying that such a temperature detection circuit is also applied to a digital heat sensor for houses as described later. 5 and 6 show an example of a digital heat sensor for a house according to the present invention.

The digital heat detector D for a house does not require a fire receiver, and is used by attaching the main body 10 to a ceiling or a wall in a house. Connect to a power outlet in your home for use. A protection frame 11 is provided at the center of the surface of the main body 10, and a part of the thermistor TH constituting the temperature detection circuit is exposed from the protection frame 11. On the left and right sides of the protection frame 11, a test switch SW, a speaker 12 for outputting an alarm sound when a fire, a disconnection or a short circuit occurs, and an alarm display means 8
Are provided.

FIG. 6 shows an internal circuit of such a residential digital heat sensor D. The main part of this internal circuit is
This is the same as the above-described digital heat sensor, and includes a temperature detection circuit 2, A / D conversion means 3 for converting a voltage output of the temperature detection circuit 2 into a temperature measurement value of a digital signal, this temperature measurement value, and disconnection. , An alarm, and a short circuit are compared with each other to determine a disconnection, an alarm, and a short circuit, and a determination signal from the determination unit 4 displays an alarm for the disconnection, an alarm, and a short circuit. Alarm display means 8 and test switch S
A configuration including an operation check circuit 9 having W, a power supply circuit 10 having an insertion plug to be driven by receiving power from a commercial power supply in the home, and converting a commercial power supply to an internal power supply. It has become.

According to such a configuration, it is not necessary to perform an operation test by applying heat from the outside, and it is possible to input test value data to the discriminating means 4 and to discriminate an abnormal operation only by operating the test switch SW. . Further, the alarm display means 8 may output an alarm sound or an alarm sound in the case of an abnormal operation in the same manner as in the case of the above-described digital heat sensor. It may be possible to output an alarm sound at a normal time so that it can be confirmed.

Next, the operation of the digital heat sensor of the present invention for discriminating disconnection, alarm, and short circuit will be described. FIG.
Steps 100 to 106 are flowcharts showing the basic procedure of the discriminating operation. Note that this discriminating operation is performed as shown in FIG.
This is a basic operation when the temperature detection circuit shown in FIG.

The voltage output of the temperature detection circuit 2 is converted into a digital signal by the A / D conversion means 3 and becomes a measured temperature value Da. Here, if the A / D converter 3 uses, for example, an 8-bit A / D converter, the divided output Vi of the temperature detection circuit can be identified at 226 levels from the minimum value 0 to the minimum value 255.
The measured temperature value Da is sequentially compared with threshold values Dc, Dj, and Ds of disconnection, alarm, and short circuit in the determination unit 4.

Here, the threshold value D for disconnection, short circuit, and alarm
c, Dj, and Ds may be set to the following values. That is, when the thermistor TH is disconnected or the resistor R is short-circuited, the divided voltage output becomes the ground level (0 V).
, The measured temperature value Da becomes zero. Therefore, the disconnection threshold value Dc may be set to a value that takes into account the measured temperature value of the partial pressure output at −25 ° C., which is the lower limit of the operating temperature of the heat sensor at normal times.

A thermistor T as a temperature detecting element
When H is short-circuited or the resistor R is disconnected, the divided voltage output becomes almost equal to VDD which is the maximum value, and the measured temperature value Da is 255 at this time. Therefore, the short-circuit threshold value Ds may be set to a value that takes into account, for example, the temperature measurement value of the partial pressure output at 100 ° C., which is the upper limit of the operating temperature of the heat sensor in normal operation.

On the other hand, when a fire occurs, the surrounding temperature rises. For example, a temperature measurement value of the partial pressure output at 40 ° C. at which a normal fire can be determined is set as the alarm threshold Dj.
A relationship of 0 <disconnection threshold Dc <report threshold Dj <short circuit threshold Ds <255 holds between these thresholds. Thus, steps 100 to 106 in FIG.
As a result, disconnection, alarm, and short-circuit signals are set, and the output circuits 5 of the digital heat sensors A to C send short-circuit, disconnection, and alarm signals to the fire receiver 7 through the monitoring line 6, thereby causing a fire. If the receiver 7 receives this, it is possible to distinguish between a short circuit, a disconnection, and an alarm. If there is no abnormality, the output circuit 5
Does not interrupt the fire receiver 7 and returns a reply signal when an inquiry is received from the fire receiver 7 by normal polling.

As described above, according to the digital heat sensor of the present invention, in addition to the fire alarm, the short circuit and the disconnection of the temperature detecting element can always be determined and detected. It is not necessary to perform a separate inspection, and highly reliable fire detection that does not require on-site monitoring can be performed. Also,
In the case where the alarm display means 8 is provided in the digital heat sensor, the alarm display means 8 is activated if the determination means 4 determines an abnormality. It can be determined on the spot.

In the case of a residential digital heat sensor, since there is no fire receiver, when the determination means 4 determines an abnormality, an alarm sound is displayed from the alarm display means 8 simultaneously with an alarm sound.

[0031]

As is apparent from the above description, according to the digital heat detector of the first aspect, a temperature detection circuit having a temperature detection element and a voltage output of the temperature detection circuit are digitally output. A / to convert the signal to a temperature measurement
D converting means, comparing the measured temperature value with the respective threshold values of disconnection, alarm, and short circuit, and determining the disconnection, alarm, and short circuit; Since the digital heat sensor itself includes the output circuit for outputting the signal to the monitoring line, the digital heat sensor itself can constantly monitor for an abnormality such as disconnection or short circuit of the temperature detection circuit.

According to the digital heat sensor of the second aspect, in addition to the effects of the digital heat sensor of the first aspect, the digital heat sensor further comprises an alarm display means for displaying an alarm of a disconnection, an alarm or a short circuit. By observing the digital heat sensor itself from the outside, it is possible to easily determine an abnormality such as disconnection, alarm, or short circuit. According to the digital heat sensor of the third aspect, in addition to the effect of the digital heat sensor of the second aspect, the digital heat sensor further includes an operation check circuit having a test switch. Since the operation abnormality can be determined by inputting the test value data, the operation abnormality of the internal determination means can be easily confirmed without using a heating tester or the like for the digital heat sensor.

According to the digital heat sensors described in the fourth and fifth aspects, since the specific structure of the temperature detection circuit of the digital heat sensor according to any one of the first to third aspects is shown, these effects can be obtained. Can be easily manufactured. According to the digital heat sensor for a house according to claim 6, a temperature detection circuit having a temperature detection element,
A / D conversion means for converting the voltage output of the temperature detection circuit into a temperature measurement value of a digital signal, and comparing the temperature measurement value with respective threshold values of disconnection, alarm, and short-circuit, And a warning signal for displaying a disconnection, warning, or short-circuit warning in accordance with a determination signal from the determination means, and a plug-in plug for converting a commercial power supply to an internal power supply. Since it has a power supply circuit, even when used in each home, the heat detector itself always detects self-disconnection abnormalities such as disconnection and short-circuit, so highly reliable fire detection can be performed. Since the detection result is also displayed, the result can be easily known.

According to the digital heat sensor for home use according to the seventh aspect, in addition to the effect of the digital heat sensor for home use according to the sixth aspect, an operation check circuit having a test switch is further provided. When the switch is operated, the test value data is inputted to the discriminating means, and the operation abnormality is discriminated, so that the operation test can be easily performed without performing a test using an external dryer or lighter, and There is no damage to the detector.

According to the digital heat sensor for home use according to the eighth and ninth aspects, the specific configuration of the temperature detection circuit of the digital heat sensor for home use according to any one of the sixth and seventh aspects is shown. Thus, it is possible to easily manufacture a digital heat sensor for a house that exhibits these effects.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of an internal circuit of a digital heat sensor according to the present invention.

FIG. 2 is a block diagram showing an example of an internal circuit of the digital heat sensor according to the present invention.

FIG. 3 is a block diagram showing an example of an internal circuit of another digital heat sensor according to the present invention.

FIGS. 4A and 4B are circuit diagrams each showing an example of a temperature detection circuit used in the digital heat detector of the present invention.

FIG. 5 is an external perspective view showing one embodiment of a digital heat sensor for a house according to the present invention.

FIG. 6 is a diagram showing a configuration of an internal circuit of the digital heat sensor for a house according to the present invention.

FIG. 7 is a flowchart showing an operation of determining disconnection, alarm, and short circuit in the present invention.

FIG. 8 is a block diagram showing an example of an internal circuit of a conventional heat detector having a temperature detection circuit.

FIG. 9 is a table showing a basic operation in a conventional heat detector.

[Explanation of symbols]

 A, B, C Digital heat sensor D Residential digital heat sensor 2 Temperature detection circuit 3 A / D conversion means 4 Judgment means 5 Output circuit 6 Monitoring line 7 Fire receiver 8 Alarm display means 9 Operation check circuit 10 Power supply circuit SW Test switch TH Thermistor (Temperature detection element) R Resistance element Da Temperature measurement value Dc Disconnection threshold Dj Alert threshold Ds Short-circuit threshold

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[Procedure amendment]

[Submission date] August 6, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing an example of the internal configuration of a conventional heat detector having a temperature detecting circuit. The heat sensor 100 includes a resistance element R1 connected in series to a thermistor TH having a large resistance value change in response to a change in ambient temperature, and a resistance element R2 serving as a reference resistance further connected to the series circuit.
A series circuit of R3 and R3 is connected in a bridge to form a temperature detection circuit 102. The comparator 101 determines a change in the output of the temperature detection circuit 102, and turns on and off the transistor Tr to monitor the temperature. The fire signal is output to the fire receiver 7 through the line 6.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0003

[Correction method] Change

[Correction contents]

Therefore, in such a heat sensor, when a fire occurs, the thermistor TH increases with an increase in ambient temperature.
, The divided voltage Vi of the resistance element R1 becomes larger than the divided voltage Vo of the reference resistance element R3, and the comparator 101 outputs an H-level signal. As a result, the transistor Tr is turned on and the monitoring line 6 is short-circuited to the ground level through the transistor Tr and the resistance element R4. The fire receiver 7 detects this state and outputs a fire alarm.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

On the other hand, since the resistance value of the thermistor TH does not always decrease as much as in a fire, the resistance element R1
Is smaller than the divided output Vo of the reference resistor R3, the comparator 101 outputs an L-level signal. As a result, the transistor Tr is turned off, so that the monitoring line 6 is not short-circuited, and the fire receiver does not output a fire alarm. FIG. 9 is a table showing the basic operation of this conventional heat sensor.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

However, in the above-described heat detector, as can be understood from FIG. 8, the magnitude of the divided output Vi of the resistance element R1 on the thermistor side and the divided output Vo of the reference resistance element R3 is large. Is compared only by the comparator, so that there are the following problems. That is, the thermistor T
If H is short-circuited or the resistor element R1 is disconnected, the divided voltage Vi on the thermistor TH side becomes almost the power supply voltage VDD and becomes larger than the divided voltage Vo on the reference resistor element side. For this reason, the transistor Tr is turned on in the same manner as in the case of a fire, and an erroneous fire is generated even though no fire has occurred.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

When the thermistor TH is disconnected or the resistor R1 is short-circuited, the voltage output Vi on the thermistor TH side is almost at the ground level, and the voltage output Vo on the reference resistor element side. Smaller. Therefore, the transistor Tr is turned off in the same manner as in the normal state, and the abnormality is not reported despite the occurrence of the abnormality.

[Procedure amendment 6]

[Document name to be amended] Drawing

[Correction target item name] Fig. 8

[Correction method] Change

[Correction contents]

FIG. 8

[Procedure amendment 7]

[Document name to be amended] Drawing

[Correction target item name] Fig. 9

[Correction method] Change

[Correction contents]

FIG. 9

Claims (9)

[Claims] 1. A digital heat sensor used by being connected to a monitoring line of a fire receiver, etc., comprising: a temperature detection circuit having a temperature detection element; A to convert to measured value
/ D conversion means, comparing the measured temperature value with the respective threshold values of disconnection, alarm, and short circuit, and determining the disconnection, alarm, and short circuit, and determining the determination signal from the determination means. A digital heat sensor, comprising: an output circuit that outputs to the monitoring line. 2. The digital heat sensor according to claim 1, further comprising alarm display means for displaying an alarm indicating a disconnection, an alarm, or a short circuit according to a judgment signal from said judgment means. 3. A digital apparatus according to claim 2, further comprising an operation check circuit having a test switch, wherein when the test switch is operated, test value data is input to said discriminating means so that an operation abnormality can be discriminated. Heat detector. 4. The temperature detecting circuit according to claim 1, wherein said temperature detecting circuit comprises a voltage dividing circuit in which a resistance element is connected in series to a thermistor, and a voltage dividing output of said resistance element is taken out. Digital heat detector. 5. The temperature detecting circuit according to claim 1, wherein the temperature detecting circuit comprises a voltage dividing circuit in which a resistance element is connected in series to the thermistor, and a voltage divided output of the thermistor is taken out. Digital heat detector. 6. A digital heat sensor for a house to be used by being attached to a ceiling or a wall in a house, comprising: a temperature detecting circuit having a temperature detecting element; A to convert to measured value
/ D converting means, comparing this temperature measurement value with the respective threshold values of disconnection, alarm, and short circuit, and determining the disconnection, alarm, and short circuit, and using a determination signal from the determination means. A digital heat sensor for residential use, comprising: alarm display means for displaying an alarm indicating disconnection, alarm, or short circuit, and a power supply circuit having a plug-in plug and converting commercial power to internal power. 7. A house according to claim 6, further comprising an operation check circuit having a test switch, wherein when the test switch is operated, test value data is input to said discriminating means so that operation abnormality can be discriminated. For digital heat sensor. 8. The house according to claim 6, wherein said temperature detecting circuit comprises a voltage dividing circuit in which a resistance element is connected in series to a thermistor, and a voltage dividing output of said resistance element is taken out. Digital heat detector. 9. A residential digital system according to claim 6, wherein said temperature detecting circuit comprises a voltage dividing circuit in which a resistance element is connected in series to a thermistor, and the voltage dividing output of said thermistor is taken out. Heat detector.