JPH0695357B2 - Semiconductor thermal sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor thermal sensor using a thermistor.

BACKGROUND ART As a conventional heat detector, there is a constant temperature type heat detector shown in FIG. This heat detector uses a bimetal 8, and when the ambient temperature reaches the reversal temperature (50 ° C to 150 ° C) of the bimetal 8, the bimetal 8 is inverted as shown by the broken line in the figure,
By closing the contact 9, the output lines 10 are short-circuited and a fire signal is output.

However, recently, there is a device using a thermistor Th as a constant temperature sensor having a completely different principle. This thermistor
Th is a kind of semiconductor whose resistance value changes when the temperature changes. In the following description, the case of using a negative characteristic thermistor whose resistance value decreases as the temperature rises will be described. Needless to say, a positive temperature coefficient thermistor may be used.

FIG. 6 shows a sensing circuit of a constant temperature type thermal sensor using the thermistor Th. In this circuit, since the resistor Ra is connected to the output of the constant voltage circuit 3 via the thermistor Th, the voltage Va across the resistor Ra rises with the resistance value of the thermistor Th which becomes smaller as the ambient temperature rises. Voltage across resistor Ra
Va is compared with the reference voltage by the comparison circuit 2 and the ambient temperature is monitored. When the voltage Va across the resistor Ra exceeds the reference voltage, the output of the comparison circuit 2 causes the switching circuit 4 to be connected to the fire receiver. The line 1 is short-circuited to send a fire signal to the fire receiver.

The appearance of such a heat detector is shown in FIG. In this heat sensor, a match rod-shaped thermistor Th is erected on a printed circuit board on which the circuit portion 7 housed in the body 6 is mounted, and the heat sensitive portion at the tip of the thermistor Th is exposed to the outside of the body 6, It is designed to improve the thermal response. This thermistor Th cannot be said to have a durable structure, and therefore, the lead wire of the thermistor Th may be broken due to mischief or the like and the thermistor Th may be opened. In this way, when the thermistor Th opens, the resistance value of the thermistor Th becomes infinite, and the voltage Va across the resistor Ra increases.
Is 0V. That is, no matter how much the ambient temperature rises in this state, the voltage Va across the resistor Ra does not rise, which causes a fatal problem of false alarm. By the way, the thermistor Th
If the lead wire is short-circuited, it is the same as the resistance value of the thermistor Th becoming 0Ω, so that the abnormality can be notified in the form of a false alarm.

[Object of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor thermal sensor capable of reporting an abnormality even when the thermistor is in an open state. To provide.

DISCLOSURE OF THE INVENTION (Structure) The present invention is a semiconductor in which a series circuit of a thermistor and a resistor is connected to a constant voltage power source, and a signal corresponding to a divided voltage by the thermistor and the resistor is output to a fire receiver as a fire signal. The thermal sensor is equipped with a comparison circuit that detects the open state of the thermistor from the divided voltage.When the open state of the thermistor is detected by the comparison circuit, the output is fired in the same signal form as the fire signal. When the comparator circuit detects the open state of the thermistor, it sends a signal indicating that the thermistor is in the open state to the fire receiver in the same signal form as the fire signal. It is also possible to notify an abnormality even when is opened.

(Embodiment) FIG. 1 and FIG. 2 show an embodiment of the present invention. In this embodiment, the open state of the thermistor Th is detected by using the comparator circuit 1 shown in FIG. 1. This comparator circuit 1 is composed of an op amp OP ₁ and the voltage of the constant voltage circuit 3 is set to the resistance R ₁ ,
It has been created reference voltage Vb by dividing by R ₂ min, the reference voltage
Vb is the voltage across the resistor Ra connected in series with the thermistor Th
The open state of the thermistor Th is detected in comparison with Va. As the operational amplifier OP ₁ , a single power supply that can exhibit a sufficient comparison function even when the input voltage is around 50 mV to 10 mV is used. In other words, in this embodiment, the open state of the thermistor Th is detected from the voltage Va across the resistor Ra, which is the same as that in the comparison circuit 2 for making a fire determination, and in such a heat detector, the power consumption is reduced as much as possible. , Thermistor Th has a very large resistance value of about 2 MΩ at 25 ° C. Also, the resistance Ra is set to a resistance value equivalent to the resistance value of the thermistor Th at the fire detection temperature (about 500 kΩ), and the rate of change of Va near the fire detection temperature is increased to improve the fire detection accuracy. . Moreover, the operating temperature range of the heat sensor of this embodiment is -10 ° C or higher, and it must function normally at -10 ° C. Since the resistance value of the thermistor Th at −10 ° C. is several 10 MΩ, the reversal temperature of the comparison circuit 1 must be set to −10 ° C. or lower. For example, when the resistance value of the thermistor Th is 40 MΩ, the voltage Va across the resistor Ra is (V _DD = 8V, Ra = 500kΩ)
Because it will be about 100 mV.

When the comparison circuit 1 is used for a heat detector whose sensor line 1 has a low impedance at the time of the above-mentioned alarm, the output of the comparison circuit 1 is input to the switching circuit 4 as shown in FIG.
As in the case of the comparison circuit 2, the switching circuit 4 sets the sensor line 1 to a low impedance to notify the fire receiver of the abnormality in the same manner as when the thermistor Th is short-circuited. That is, the thermistor Th
When is short-circuited, the voltage Va across the resistor Ra rises to the power supply voltage _VDD as in the case of a fire. At this time, the output of the comparison circuit 2 causes the switching circuit 4 to make the sensor line 1 have a low impedance. Therefore, even when the thermistor Th is opened, the output of the comparison circuit 1 causes the switching circuit 4
If the sensor line 1 is operated so as to have a low impedance, the fire receiver side can be notified of an abnormality in the thermistor Th. In this case, the fire receiver cannot identify whether the thermistor Th is short or open, or whether there is a fire, but at least some abnormality should be detected by the fire receiver. Can be informed. Therefore, it is possible to prevent the fatal defect of false alarm caused by the open state of the thermistor Th.

However, as described above, it is not always necessary to send the output of the comparison circuit 1 to the fire receiver side in exactly the same signal form as at the time of a fire occurrence, and it is possible to detect that there is something wrong with the semiconductor heat detector side. Any signal form shown on the machine side may be used.

Such an embodiment is shown in FIG. In this embodiment, the present invention is applied to an analog output type heat sensor which sends a temperature change as a change in output voltage to a fire receiver. In this analog output type heat sensor, the analog voltage conversion circuit 5
The voltage Va across Ra is converted into a voltage output Vs and sent to the fire receiver. For example, as shown in Fig. 4, 1V at an ambient temperature of 40 ° C or lower
When the ambient temperature rises above 40 ° C, the voltage output Vs gradually increases, and at 80 ° C Vs = 5V, so that it does not rise any further. It should be noted that it is designed to output a voltage of 1 V when the temperature is 40 ° C. or lower because the analog output type heat sensor is not operating normally due to disconnection or failure of the sensor line 1 in the fire receiver. This is to detect. Therefore, when the thermistor Th is opened, the output of the analog voltage conversion circuit 5 falls below the failure detection level Vt at which the fire receiver judges that the analog output type heat sensor has failed, as shown by the broken line in FIG. By pulling down, the fire receiver can judge that there is any abnormality on the analog output type sensor side including the sensor line 1. In this case, the comparison circuit 1'is configured so that the output becomes low level when the thermistor Th is opened, and the output of the analog voltage conversion circuit 5 is received through the diode D as described above. It is designed to be lowered below the machine failure detection level Vt. Even in this case, when the comparator circuit 1'detects the open state of the thermistor Th, its output is notified to the fire receiver side by a line abnormality signal, that is, in the same signal form as the fire signal. It is possible to prevent the fatal defect of being lost.

[Effects of the Invention] As described above, the present invention connects a series circuit of a thermistor and a resistor to a constant voltage power source, and outputs a signal corresponding to a divided voltage by the thermistor and the resistor as a fire signal to a fire receiver. In the semiconductor thermal sensor, a comparison circuit for detecting the open state of the thermistor from the divided voltage is provided, and when the open state of the thermistor is detected by the comparison circuit,
Since the output is output to the fire receiver in the same signal form as the fire signal, the fire receiver cannot determine whether the thermistor is open or a fire has occurred, but there must be at least some abnormality. Can be notified to the fire receiver side, which has the effect of not causing the fatal drawback of a false alarm when the thermistor is open.

[Brief description of drawings]

FIG. 1 is a specific circuit diagram of a comparison circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a general type heat sensor having the same as above, and FIG. 3 is an analog output type heat sensing having the same as above. FIG. 4 is a circuit diagram of the thermometer, FIG. 4 is an explanatory view of the analog voltage conversion circuit output of the same, FIG. 5 is a cross-sectional view of a main part of a constant temperature type thermal sensor using a bimetal of a conventional example, and FIG. FIG. 7 is a side view showing the external appearance of the same. Reference numeral 1 is a comparison circuit, Th is a thermistor, and Ra is a resistor.

Claims (1)

[Claims] 1. A semiconductor-type thermal detector for connecting a series circuit of a thermistor and a resistor to a constant voltage power source, and outputting a signal corresponding to a divided voltage by the thermistor and the resistor as a fire signal to a fire receiver in the thermistor. Comprising a comparator circuit that detects the open state of the above from the divided voltage, and when the comparator circuit detects the open state of the thermistor, its output is output to the fire receiver in the same signal form as the fire signal. A semiconductor-type heat sensor characterized by.