JPH07234979A - Heat sensor - Google Patents

Abstract

(57) [Summary] [Purpose] When temperature is detected by applying multiple levels of constant current to the thermistor, switching of constant current is performed quickly and error of constant current value is reduced. [Structure] A resistor R1 is provided at the + input terminal of the differential amplifier OP.
A constant voltage E ′ is applied by R1 and R12, and a constant current having a different value for each detection temperature region is detected on the output terminal side of the differential amplifier OP so that it can be detected in a linear resistance region where the characteristics of the thermistor TH stand. Analog switches S1, S2, S3 and resistors R11 to R1 for applying I to the thermistor TH
8 is connected. Analog switch S1, S2, S
3 turns on or off according to the environmental temperature, and resistors R11 to R
The combined resistance value of 18 changes and the current value I changes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat detector using a thermistor, and more particularly to a heat detector detecting a temperature by applying a constant current having a plurality of levels to the thermistor.

[0002]

2. Description of the Related Art Generally, the characteristics of a thermistor are linear in a narrow temperature range, but in the case of a fire detector, it is -20 °
Since a wide temperature range such as 100 ° C. has to be covered, the rate of change inevitably decreases in the low temperature range and the high temperature range, and the measurement accuracy and resolution deteriorate.

Therefore, for example, the resistance value RTH of the thermistor TH having a negative characteristic is high in the low temperature (L) range and high in the high temperature (H) range.
Since the resistance is low in the range, as shown in FIG. 3, the boundary between the L range and the H range is 40 °, and in each temperature range, 5V is set as a full scale and the range of 1 to approximately 4V is detected. The constant currents I _LOW and I _High are applied so as to detect the low temperature and high temperature regions of the characteristic where the rate of change of the thermistor TH is small, and to detect the linear region where the characteristic stands. Further, in the case of detecting the disconnection of the thermistor TH, a current I _open which is lower than the constant current I _LOW of the L range is applied to detect a voltage of 4 V or more in a linear region where the resistance characteristic of the thermistor TH stands. In this case, it is determined that the wire is broken.

FIG. 10 shows the constant currents I _open , I _LOW and I
_The conventional constant current circuit which changes like _High and applies to a thermistor is shown. One ends of analog switches SW1 and SW2 and resistors R1 and R5 are connected to the + line. The other end of the resistor R1 is connected to the other end of the switch SW2 and the resistor R
2 is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the switch SW1.
Of the resistor R3 and one end of the resistor R3. The other end of the resistor R3 is connected to the + input terminal of the differential amplifier OP and one end of the resistor R4, and the other end of the resistor R4 is grounded.

The other end of the resistor R5 is connected to the-input terminal of the differential amplifier OP and the emitter of the PNP type transistor Q, and the output terminal of the differential amplifier OP is connected to the base of the transistor Q. The collector of the transistor Q is grounded via the thermistor TH having a negative characteristic, and the thermistor T
The temperature is detected by the voltage V _TH (= I · R _TH ) across H.

In such a configuration, the differential amplifier OP
Input voltage of + input terminal of-is the same as each input voltage,
The current I flowing through the thermistor TH is the switch SW1, SW
When both 2 are off, I = {E- (R1 + R2 + R3) E / (R1 + R2 + R
3 + R4)} / R5 = I _{open When the} switch SW2 is on and the switch SW1 is off, I = {E− (R2 + R3) E / (R2 + R3 + R4)}
When / R5 = I _LOW switch SW1 is on, I = {E−R3 · E / (R3 + R4)} / R5 = I _High , that is, I _open <I _LOW <I _High .

[0007]

However, in the above-mentioned constant current circuit of the conventional heat detector, the input voltage to the + input terminal of the differential amplifier OP is switched by the ON / OFF control of the switches SW1 and SW2. For differential amplifier O
By the influence of the slew rate of P, the constant current in the actually switched range is supplied to the thermistor, as shown in FIG.
As shown in, a delay of, for example, several tens of μsec or more occurs, and the environmental temperature, that is, the voltage V _TH across the thermistor _TH
There is a problem that (= I · R _TH ) cannot be taken in quickly. Further, if this range switching is performed for each polling from the receiver, when a plurality of such heat sensors are connected to the transmission line, the polling cycle becomes long.

Further, in the case of the system in which the input voltage to the + input terminal of the differential amplifier OP is changed, when the input voltage becomes large, the offset of the differential amplifier OP affects and the difference between the constant current values to be switched becomes large. At times, there is a problem that the accuracy of the constant current value is poor and the error becomes large. In view of the above-mentioned conventional problems, the present invention is capable of quickly switching the constant current and reducing the error in the constant current value when temperature is detected by applying constant currents of multiple levels to the thermistor. The purpose is to provide a sensor.

[0009]

In order to achieve the above object, the present invention provides a heat detector for detecting a fire by detecting an environmental temperature based on a voltage corresponding to a resistance value of a thermistor, with a constant input. The load resistance has a constant current circuit equipped with a differential amplifier that drives the output stage transistor unit with a constant current so that the feedback voltage corresponding to the output current matches the voltage, and the resistance value can be switched between the power supply lines. , The output-stage transistor section of the constant current circuit and the thermistor are connected in series, and the resistance value of the load resistor is different for each detection temperature region so that the temperature can be detected in the linear resistance region of the thermistor. It is characterized in that a switching circuit for switching so as to obtain a constant current value is provided.

A specific example is characterized in that the environmental temperature is detected by measuring the voltage across the thermistor. The present invention is also characterized in that the load resistor connects a plurality of resistors in series and the switching circuit switches the resistance value of the load resistor by selectively short-circuiting the plurality of resistors. To do.

Further, according to the present invention, when detecting the disconnection of the thermistor, the constant current circuit controls so that the constant current circuit applies a different current which can be detected in the linear resistance region where the characteristics of the thermistor stand. And a control means for determining whether or not the thermistor is disconnected based on the voltage corresponding to the resistance value of the thermistor in this state.

[0012]

In the heat detector provided with the constant current circuit according to the present invention, a constant voltage is applied to the input terminals of the differential amplifier, and the resistance of the load resistance connected to the output terminal side of the differential amplifier. The constant current of the value obtained by switching the value for each detection temperature region is applied to the thermistor, so the slew rate of the differential amplifier does not affect and the constant current value changes quickly at the time of switching, so for each range. The temperature can be detected quickly.

Further, since the voltage applied to the input terminals of the differential amplifier can be made constant, there is no influence of the offset even if the difference in the constant current values greatly differs, and the error in the constant current value can be reduced.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an analog type heat sensor according to the present invention. In FIG. 1, a rectifier circuit 1 is connected to a repeater or receiver (not shown) via a sensor line composed of a signal line S and a common line SC, and a DC power supply voltage is supplied from the repeater or receiver. At the same time, a calling signal as described later is applied. The sensor line S,
One or more sensors are connected to the SC.

The DC voltage supplied via the sensor lines S, SC is depolarized by the rectifier circuit 1 and then the noise is absorbed by the noise absorption circuit 2. Next, the constant voltage circuit 4a generates a constant voltage of + 10V for analog circuits, and the constant voltage circuit 4b generates a constant voltage of + 5V for circuits such as MPU. In addition, a response signal to the call signal from the repeater or receiver is generated by the response signal circuit 3 as a current, and the noise absorption circuit 2 and the rectification circuit 1
Will be replied via.

The voltage detection circuit 5 turns on the current switches 6a and 6b when the output voltage of the constant voltage circuit 4a exceeds a predetermined value when the sensor rises. Constant voltage circuit 4a
Of the output voltage of the constant current circuit 7 and the thermistors TH and A having negative characteristics as shown in detail in FIG. 2 via the current switch 6a.
/ D reference voltage circuit 8 and the constant voltage circuit 4b
Output voltage of M is for transmission processing via the current switch 6b.
It is supplied to the PU (1) 9a and the MPU (2) 9b for signal processing. Here, as an example, the MPU 9a for transmission processing has a master clock of 400 KHz, and the MPU 9b for signal processing has 2 MHz.

Voltage V _TH according to the resistance value of the thermistor _TH
Is taken in by the signal processing MPU 9b, and the reference value RE for the A / D conversion scale by the A / D reference voltage circuit 8 is obtained.
A / D conversion is performed based on F. Further, the constant current circuit 7 applies variable constant currents I _open , I _LOW , and I _High (I _open <I _LOW <I _High ) to the thermistor TH by the control of the signal processing MPU 9b, and the MPU 9b has a three-step current range. Is configured to detect temperature.

The constant current circuit 7 will be described with reference to FIGS. Analog switches S1 and S on the + line
2, one end of each of the resistors R11 and R13 is connected, and the analog switches S1 and S2 and an analog switch S3 described later are controlled by the signal processing MPU 9b. The other end of the resistor R11 is connected to the + input terminal of the differential amplifier OP and one end of the resistor R12, and the other end of the resistor R12 is grounded. Therefore, the input voltage E '= of the + input terminal of the differential amplifier OP
{E−R11 · E / (R11 + R12)} is always constant.

The other ends of the analog switch S2 and the resistor R13 are both connected to one end of a variable resistor R14 for current value adjustment, and the other ends of the analog switch S1 and the variable resistor R14 are both variable resistors for current value adjustment. It is connected to one end of R15. The other end of the variable resistor R15 is connected to one end of the resistor R16, and the other end of the resistor R16 is connected to the-input terminal of the differential amplifier OP, one end of the capacitor C and the emitter of the PNP transistor Q2. The output terminal of the differential amplifier OP is connected to the other end of the capacitor C and one end of the base resistor R19.

The other end of the base resistor R19 is connected to the base of the PNP transistor Q1, and the emitter of the transistor Q1 is connected to the base of the transistor Q2. The collectors of the transistors Q1 and Q2 are both connected to the thermistor TH and one end of a resistor R17.
The other end of is connected to the resistor R18 and one end of the analog switch S3. The thermistor TH, the resistor R18, and the other end of the analog switch S3 are all grounded.

In such a constant current circuit 7, the input voltages of the + input terminal and the-input terminal of the differential amplifier OP are the same, and the current I flowing through the thermistor TH is E '= {E-R1.
1 · E / (R11 + R12)}, the current flowing on the side of the resistor R17 is I ′, and when the analog switches S1 to S3 are both off, I = E ′ / (R13 + R14 + R15 + R16) −I ′
= I _open analog switch S2 is on, analog switch S1,
When S3 is both off, I = E '/ (R14 + R15 + R16) -I' = I _{LOW When} analog switches S1 and S3 are both on, and analog switch S2 is off, I = E '/ (R15 + R16) -I '= I _High , that is, I _open <I _LOW <I _High .

The analog switch S3 is linear in both the low temperature (L) range and the high temperature (H) range by switching the combined resistance value of the resistors R17 and R18 connected in parallel to the thermistor TH to R17 or R17 + R18. It is used to obtain characteristics. Further, the resistance value R _TH of the thermistor having a negative characteristic is high in the L range,
Since the resistance is low in the H range, as shown in FIG.
Make sure that the boundary between the range and the H range is 40 °, and that in each temperature range, the range of 1 to approximately 4 V is detected with 5 V as the full scale, and the low temperature and high temperature regions of the characteristic that the rate of change of the thermistor TH is small are detected. _First , the constant currents I _LOW and I _High are set so as to detect a linear region where the characteristics stand out. When detecting a wire breakage, the thermistor T is set by setting the current I _open to be lower than the constant current I _{LOW in the} L range.
In a linear region where the resistance characteristic of H stands, for example, 4V
When the above is detected, it is configured to determine the disconnection.

Returning to FIG. 1, the ringing signal transmitted from the repeater or receiver is detected by the ringing detecting circuit 10 via the sensor lines S, SC, the rectifying circuit 1 and the noise absorbing circuit 2, and the detection signal is detected. Is applied to the transmission processing MPU 9a. The address setting circuit 11 is composed of, for example, a DIP switch or the like, and the address of this sensor is preset.
When the power is turned on from the constant voltage circuit 4b, the transmission processing MPU 9a is initialized and then reads this address. Similarly, the model setting circuit 13 is also configured by a DIP switch or the like, and a type code indicating a heat detector or a smoke detector is preset, and the signal processing MPU 9b is a constant voltage circuit 4
When the power is turned on from b, the type code is read after being initialized, and then the mode is changed to the stop mode.

1 from the repeater or receiver to this sensor
The calling signal of the frame is, for example, as shown in FIG. 4, the reset pulse RST and the sensor lines S and SC sent at the beginning.
It is composed of a plurality of polling pulses P sequentially sent at a predetermined interval according to the number of the above sensors, and a response signal is returned from each sensor during each polling pulse P. The width of the reset pulse RST is set to be longer than that of the polling pulse P, and the sensor line S,
The address counters in the MPU 9a for transmission processing of all the sensors on the SC are reset.

Next, the address counter counts the polling pulse P following the reset pulse RST, and when the count number and the address set via the address setting circuit 11 match, the transmission processing MPU 9a calls itself. Identify and / STOPC generation circuit 12
MP for signal processing via (“/” is used for inverted signal)
Start U9b.

Here, the signal processing MPU 9b receives the input port / S when the input signal of the input port D0 is at the low level.
When the input signal of TOPC becomes low level, the mode changes from stop mode to active mode, and the input port D
When the input signal of 0 goes high, the active mode is switched to the stop mode. This will be described in detail with reference to FIG.
When the U9a identifies the call addressed to itself, it outputs an active signal (D2 output in the figure, the same applies below) that goes low until the polling pulse of the next address is detected.
2 to / STOPC generation circuit 12 and signal processing MPU 9
b to the input port D0, and then to ports D4 and D
3, the output of D6 is generated in this order, and the MPU for signal processing is generated.
9b is applied. In the / STOPC generation circuit 12, when the D2 output of the transmission processing MPU 9a becomes low level, the output signal / STOPC becomes high level after a predetermined time elapses. Switch to active mode.

Next, the operation of the transmission processing MPU 9a will be described with reference to the flowchart shown in FIG. First, as described above, when the power is turned on from the constant voltage circuit 4b, the address is read after being initialized, and the standby state is set. Then, when the reset pulse RST is received, the address counter is reset, and the polling pulse P is counted to monitor its own address (step S1). Then, when one's own address is identified, D2
By setting the output to the low level, the / STOPC generation circuit 12 is operated to shift the signal processing MPU 9b from the stop mode to the active mode (step S
2).

Then, when a fire is detected, a timing signal for outputting a fire bit from the signal processing MPU 9b is output from the output port D4 (step S3),
Next, a timing signal for outputting the temperature data from the signal processing MPU 9b is output from the output port D3 (step S4), and then the type data is output to the signal processing M.
A timing signal for output from the PU 9b is output from the output port D6 (step S5).

Then, it is monitored whether or not the polling pulse P indicating the next sensor address is detected (step S
6) If YES, the D2 output is shifted to the high level to shift the signal processing MPU 9b from the active mode to the stop mode (step S7). Next, the operation of the signal processing MPU 9b in the active mode will be described with reference to the flowchart shown in FIG. 6 and FIGS. First, as described above, when power is turned on from the constant voltage circuit 4b, the active mode is set, the initialized post-type data is read, and then the stop mode is entered. After that, when the mode is shifted to the active mode under the control of the transmission processing MPU 9a, the disconnection detection mode processing is executed first (step S11). In this disconnection detection mode, the analog switches S1, S2, and S3 are all turned off, the current of the constant current circuit 7 is set to the disconnection detection current I _open , and the voltage V _TH corresponding to the resistance value of the thermistor _TH is fetched and the predetermined voltage ( = 4V) or more (step S12), and if it is above a predetermined level, it is determined that the thermistor TH is disconnected (step S13), and the process proceeds to step S19.

On the other hand, when the thermistor TH is not broken, the range determination mode is entered (step S14), and first the current of the constant current circuit 7 is set to the _low range I _LOW by turning on the analog switch S2 (step S14). S15). Next, the voltage V _TH corresponding to the resistance value of the thermistor TH is taken in and the voltage (=
1 V) or less is determined (step S16), YES
In the case of, the current of the constant current circuit 7 is set to the analog switch S
By turning on S1 and S3, the high range I _High is set and the process proceeds from step S17 to step S18.
In the case of, the current of the constant current circuit 7 is left as it is and the process proceeds to step S18.

Next, the voltage V _TH corresponding to the resistance value of the thermistor TH is taken in, converted into temperature data corresponding to the range, and if judged to be a fire, the transmission processing MPU.
A fire bit is output at the timing of D4 output of 9a, then temperature data is output at the timing of D3 output of MPU 9a for transmission processing, and then D6 of MPU 9a for transmission processing is output.
The type data is output at the output timing (step S
19). Here, in the present embodiment, when it is determined that there is a disconnection, the disconnection information is returned to the repeater or the like by not outputting the type data. Then input port D
The signal of 0 is monitored (step S20), and when it becomes high level, the mode is changed to the stop mode.

Therefore, according to the above embodiment, the input voltage E '= {E-R11.multidot.
E / (R11 + R12)} is always constant, and the current I is switched on the output side of the differential amplifier OP, so that FIG.
As shown in, the time until the switching of the current I at the time of switching can be shortened.
U9b can take in the voltage VTH quickly. In particular,
The degree of freedom in designing the system can be improved when the signal processing MPU 9b switches the current I in the active mode for a short time.

The present invention can be applied to a circuit configuration in which the temperature is detected by the voltage divided by the resistors R13 to R16 instead of measuring the voltage VTH across the thermistor TH. It can also be applied to the case of positive characteristics. Further, in the above embodiment, the range at the time of detecting the environmental temperature is set to 2 ranges, but it may be 3 ranges or more.

[0034]

As described above, according to the present invention, in a heat detector for detecting a fire by detecting an environmental temperature based on a voltage corresponding to a resistance value of a thermistor, a constant input voltage and an output current are applied. A constant-current circuit having a differential amplifier that drives the output-stage transistor unit with a constant current so that the corresponding feedback voltages match, and a load resistor whose resistance value can be switched between power supply lines, An output stage transistor section and the thermistor are connected in series, and a constant current value having a different value for each detected temperature region is obtained so that the resistance value of the load resistor can be detected in the linear resistance region of the thermistor. Since a switching circuit for switching is provided, a constant voltage is applied to the input terminals of the differential amplifier, and the resistance value of the load resistance connected to the output terminals of the differential amplifier is detected in the temperature range. The constant current of the value obtained by switching to is applied to the thermistor, so the slew rate of the differential amplifier is not affected, and the constant current value changes rapidly at the time of switching, so the temperature is detected quickly for each range. be able to.

Further, since the voltage applied to the input terminals of the differential amplifier can be made constant, even if there is a large difference in constant current value, there is no effect of offset, and the error in constant current value can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a heat sensor according to the present invention.

FIG. 2 is a circuit diagram showing the constant current circuit of FIG. 1 in detail.

FIG. 3 is an explanatory diagram showing an environmental temperature detection range and a wire breakage detection range of the thermistor shown in FIG.

FIG. 4 is a timing chart showing control signals between the transmission processing MPU and the signal processing MPU of FIG.

5 is a flowchart for explaining the operation of the transmission processing MPU of FIG.

FIG. 6 is a flowchart for explaining the operation of the signal processing MPU of FIG.

7 is a timing chart showing a current switching operation of the signal processing MPU of FIG.

FIG. 8 is an explanatory diagram showing a switching operation of the switch of FIG.

FIG. 9 is an explanatory diagram comparing the current switching speeds of the example and the conventional example.

FIG. 10 is a circuit diagram showing a constant current circuit of a conventional heat detector.

[Explanation of Codes] 1: Rectifier circuit 2: Noise absorption circuit 3: Response signal circuit 4a, 4b: Constant voltage circuit 5: Voltage detection circuit 6a, 6b: Current switch 7: Constant current circuit 8: A / D reference voltage circuit 9a, 9b: MPU (microprocessor) 10: Call detection circuit 11: Address setting circuit 12: / STOPC generation circuit 13: Model setting circuit TH: Thermistor S1, S2, S3: Switch OP: Differential amplifier Q1, Q2: Transistor R11 to R19: resistor C: capacitor

Claims (4)

[Claims] 1. A heat detector for detecting a fire by detecting an environmental temperature based on a voltage according to a resistance value of a thermistor, so that a feedback voltage according to an output current matches a constant input voltage. A constant current circuit having a differential amplifier that drives the output stage transistor section with a constant current is provided, and a load resistance whose resistance value can be switched between power supply lines, an output stage transistor section of the constant current circuit, and the thermistor are connected in series. And a switching circuit for switching the resistance value of the load resistor so that a constant current value having a different value can be obtained for each detection temperature region where the temperature can be detected in the linear resistance region of the thermistor. And a heat detector. 2. The heat sensor according to claim 1, wherein the ambient temperature is detected by measuring the voltage across the thermistor. 3. The thermal sensor according to claim 1, wherein:
The load resistor is configured by connecting a plurality of resistors in series, and the switching circuit switches the resistance value of the load resistor by selectively short-circuiting the plurality of resistors. 4. The thermal sensor according to claim 1, further comprising: when detecting the disconnection of the thermistor, a current having a different value which can be detected in a linear resistance region where the characteristic of the thermistor stands. A constant current circuit is controlled so as to apply to the thermistor, and a control means for judging whether or not the thermistor is disconnected based on the voltage according to the resistance value of the thermistor in this state. vessel.