JP3043940B2 - 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 heat sensor using a thermistor, and more particularly to a heat sensor which detects a temperature by applying a constant current of a plurality of levels to the thermistor.

[0002]

2. Description of the Related Art In general, the characteristics of a thermistor are linear in a narrow temperature range, but in the case of a fire detector, it is -20 ° or more.
Since it is necessary to cover a wide temperature range such as 100 ° C., the rate of change is inevitably small in the low temperature range and the high temperature range, and the measurement accuracy and the resolution are deteriorated.

Therefore, for example, the resistance value RTH of the thermistor TH having a negative characteristic has a high resistance in a low temperature (L) range and a high temperature (H) in a low temperature (L) 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 set to 40 °, and in each temperature range, 5 V is set to a full scale and a range of 1 to approximately 4 V is detected. The constant currents I _LOW and I _High are applied so as not to detect the low temperature and high temperature regions of the characteristics where the rate of change of the thermistor TH is small, but to detect the linear region where the characteristics are _high . Further, when detecting a disconnection of the thermistor TH, a current I _open lower than the constant current I _LOW of the L range is applied, and for example, 4 V or more is detected in a linear region where the resistance characteristic of the thermistor TH is established. In this case, it is determined that the wire is broken.

FIG. 10 shows the above constant currents I _open , I _LOW , I
_The conventional constant current circuit which changes to _High and applies to a thermistor is shown. One end of each of analog switches SW1, SW2 and resistors R1, R5 is 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 and one end of the resistor R2 is connected to a switch SW1.
And the other 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.

[0005] The other end of the resistor R5 is connected to the negative input terminal of the differential amplifier OP and the emitter of the PNP 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 through a 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
The input voltage of the + input terminal and the input voltage of the-input terminal are the same,
The current I flowing through the thermistor TH is determined by switches SW1 and SW
2 are both off, I = ｛E− (R1 + R2 + R3) E / (R1 + R2 + R
3 + R4)｝ / R5 = I When the _open switch SW2 is on and the switch SW1 is off, I = {E− (R2 + R3) E / (R2 + R3 + R4)}.
When the / 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-described conventional constant current circuit of the heat detector, the input voltage to the + input terminal of the differential amplifier OP is switched by ON / OFF control of the switches SW1 and SW2. Differential amplifier O
FIG. 9 (b) shows that the slew rate of P influences and the constant current of the actually switched range is supplied to the thermistor.
As shown in FIG. 7, for example, a delay of several tens of microseconds or more occurs, and the environmental temperature, that is, the voltage V _TH across the thermistor TH is increased.
(= I · R _TH ) cannot be acquired quickly. Further, if this range switching is performed every polling from the receiver, if a plurality of such heat sensors are connected to the transmission line, the polling cycle becomes long.

In the case of a system in which the input voltage to the + input terminal of the differential amplifier OP is changed, when the input voltage increases, the offset of the differential amplifier OP affects, and the difference between the constant current values to be switched increases. Sometimes, there is a problem that the accuracy of the constant current value is poor and the error increases. SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention provides a heat source capable of quickly switching a constant current and reducing an error in a constant current value when temperature is detected by applying a constant current of a plurality of levels to a thermistor. It is intended to provide a sensor.

[0009]

According to the present invention, there is provided a heat sensor for detecting a fire by detecting an environmental temperature based on a voltage corresponding to a resistance value of a thermistor. A constant current circuit with a differential amplifier that drives the output stage transistor section with a constant current so that the feedback voltage according to the output current matches the voltage, and a load resistor capable of switching a resistance value between 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 has a different value for each detected temperature region so that the temperature can be detected in a linear resistance region of the thermistor. 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 a resistance value of the load resistor by selectively short-circuiting the plurality of resistors. I do.

The present invention further controls the constant current circuit to apply a current of a different value detectable in a linear resistance region where the characteristics of the thermistor rises to the thermistor when a disconnection of the thermistor is detected. And control means for determining whether or not the thermistor is disconnected based on a voltage corresponding to the resistance value of the thermistor in this state.

[0012]

In the heat sensor provided with the constant current circuit according to the present invention, a constant voltage is applied to the input terminal of the differential amplifier, and the resistance of the load resistor connected to the output terminal side of the differential amplifier. Since the constant current of the value obtained by switching the value for each detection temperature region is applied to the thermistor, the slew rate of the differential amplifier has no effect, and the constant current value changes quickly at the time of switching. The temperature can be detected quickly.

Further, since the voltage applied to the input terminal of the differential amplifier can be kept constant, even if there is a large difference between the constant current values, there is no influence of the offset and the error of 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 heat sensor according to the present invention. In FIG. 1, a repeater and a receiver (not shown) are connected to a rectifier circuit 1 via a sensor line including a signal line S and a common line SC, and a DC power supply voltage is supplied from the repeater and the receiver. At the same time, a call signal as described later is applied. In addition, the detector line S,
One or more sensors are connected to SC.

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

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

The 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.
A / D conversion is performed based on F. 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 under the control of the signal processing MPU 9b. Is configured to detect the temperature.

The constant current circuit 7 will be described with reference to FIGS. Analog switches S1 and S
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 end of the analog switch S2 and the other end of the resistor R13 are both connected to one end of a variable resistor R14 for adjusting the current value. The other end of the analog switch S1 and the other end of the variable resistor R14 are also the same variable resistor for adjusting the current value. 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 negative 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 a PNP transistor Q1, and the emitter of the transistor Q1 is connected to the base of a transistor Q2. The collectors of the transistors Q1 and Q2 are both connected to one end of the thermistor TH and one end of the resistor R17.
Is connected to the resistor R18 and one end of the analog switch S3. The other ends of the thermistor TH, the resistor R18, and 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)｝, where the current flowing to the resistor R17 side is I ′ and 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 off, I = E '/ (R14 + R15 + R16) -I' = I _{LOW When} both analog switches S1 and S3 are on, and when analog switch S2 is off, I = E '/ (R15 + R16) -I '= I _High , that is, I _open <I _LOW <I _High .

The analog switch S3 switches the combined resistance value of the resistors R17 and R18 connected in parallel to the thermistor TH to R17 or R17 + R18, so that the analog switch S3 is linear in both the low temperature (L) range and the high temperature (H) range. Used to obtain properties. Further, the resistance value R _TH of the thermistor having a negative characteristic is high resistance in the L range,
Since the resistance is low in the H range, as shown in FIG.
The range between 1 and approximately 4 V is detected so that the boundary between the range and the H range is 40 °, and 5 V is set as a full scale in each temperature range, and the low and high temperature regions having a small change rate of the thermistor TH are detected. Instead, the constant currents I _LOW and I _High are set so as to detect a linear region where the characteristics _rise . Further, when disconnection is detected, the current I _open is set lower than the constant current I _LOW of the L range, and the thermistor T is set.
In the linear region where the resistance characteristic of H stands, for example, 4V
When the above is detected, a disconnection is determined.

Returning to FIG. 1, a call signal sent from a repeater or a receiver is detected by a call detection circuit 10 via sensor lines S and SC, a rectifier circuit 1 and a noise absorption circuit 2, and the detected signal Is applied to the transmission processing MPU 9a. The address setting circuit 11 is constituted by, for example, a DIP switch or the like, and the address of the sensor is set in advance.
When power is supplied from the constant voltage circuit 4b, the transmission processing MPU 9a is initialized and reads this address. Similarly, the model setting circuit 13 is also constituted by a DIP switch or the like, and a type code indicating a heat sensor or a smoke sensor is preset, and the MPU 9b for signal processing is a constant voltage circuit 4
When the power is turned on from b, this type code is read after initialization, and then the mode shifts to the stop mode.

[0024] 1 from the repeater or receiver to this sensor
The paging signal of the frame includes, for example, a reset pulse RST sent at the beginning and the detector lines S and SC as shown in FIG.
It is composed of a plurality of polling pulses P sequentially transmitted at predetermined intervals 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 the polling pulse P, and the reset pulse RST causes the sensor lines S,
The address counter in the transmission processing MPU 9a of all the sensors on the SC is reset.

Next, the address counter counts the polling pulse P following the reset pulse RST, and when the counted number matches the address set via the address setting circuit 11, the transmission processing MPU 9a calls the self-addressed call. Identify and / STOPC generation circuit 12
("/" Is used for the inverted signal)
Start U9b.

Here, when the input signal of the input port D0 is at low level, the signal processing MPU 9b
When the input signal of the TOPC becomes low level, the mode shifts from the stop mode to the active mode.
When the input signal of 0 becomes a high level, the mode shifts from the active mode to the stop mode. This will be described in detail with reference to FIG.
When U9a identifies the call addressed to itself, U9a outputs a low-level active signal (D2 output in the figure, the same applies hereinafter) to the output port D until the detection of the next address polling pulse.
2 to / STOPC generation circuit 12 and MPU 9 for signal processing
b to the input port D0 and then to ports D4 and D4.
3, the output of D6 is generated in this order and the signal processing MPU
9b. In the / STOPC generation circuit 12, when the D2 output of the transmission processing MPU 9a goes low, the output signal / STOPC goes high after a lapse of a predetermined time. Move 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 initialization and the apparatus enters a standby state. Next, upon receiving the reset pulse RST, the address counter is reset, and the own address is monitored by counting the polling pulse P (step S1). Then, when its own address is identified, D2
By setting the output to a low level, the / STOPC generation circuit 12 is operated, and the MPU 9b for signal processing is shifted 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 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 MPU 9b.
A timing signal for output from the PU 9b is output from the output port D6 (Step S5).

Next, it is monitored whether or not the polling pulse P indicating the next sensor address has been detected (step S).
6) In the case of YES, the signal processing MPU 9b is shifted from the active mode to the stop mode by shifting the D2 output to the high level (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 the power is turned on from the constant voltage circuit 4b, the active mode is set. After initialization, the type data is read, and then the mode is shifted to the stop mode. Thereafter, when the mode shifts to the active mode under the control of the transmission processing MPU 9a, first, the processing in the disconnection detection mode is executed (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 _Iopen , and the voltage _VTH corresponding to the resistance value of the thermistor _TH is taken in and the predetermined voltage ( = 4V) or more (step S12). If the level is equal to or more than the predetermined level, the thermistor TH determines that the wire is disconnected (step S13), and proceeds to step S19.

On the other hand, if the thermistor TH is not disconnected, the mode shifts to the range determination mode (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, a voltage V _TH corresponding to the resistance value of the thermistor TH is taken in, and a voltage corresponding to 40 ° C. or more (=
1V) or not (step S16), and YES
In the case of, the current of the constant current circuit 7 is
1, the high range I _High is set by turning on S3, and the process proceeds from step S17 to step S18, where NO
In this case, the process proceeds to step S18 while keeping the current of the constant current circuit 7 as it is.

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 when it is determined that a fire has occurred, the MPU for transmission processing is determined.
9a, a fire bit is output at the timing of D4 output, then temperature data is output at the timing of D3 output of the MPU 9a for transmission processing, and then D6 of the MPU 9a for transmission processing is output.
Type data is output at the output timing (step S
19). Here, in the present embodiment, when it is determined that a disconnection has occurred, 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 the signal becomes high level, the mode shifts to the stop mode.

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

It should be noted that the present invention can be applied to a circuit configuration in which the temperature is detected by a voltage divided by the resistors R13 to R16 instead of measuring the voltage VTH across the thermistor TH. It can 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 two ranges, but may be set to three or more ranges.

[0034]

As described above, the present invention relates to 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-current circuit including a differential amplifier that drives the output-stage transistor unit with a constant current so that the corresponding feedback voltages match; a load resistor capable of switching a resistance value between power supply lines; An output stage transistor section and the thermistor are connected in series, and furthermore, 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 a linear resistance region of the thermistor. Switching circuit is provided, a constant voltage is applied to the input terminal of the differential amplifier, and the resistance value of the load resistor connected to the output terminal side of the differential amplifier is detected. Is applied to the thermistor, so that the slew rate of the differential amplifier has no effect, and the constant current value changes quickly at the time of switching, so that the temperature is detected early for each range. be able to.

Further, since the voltage applied to the input terminal of the differential amplifier can be kept constant, even if there is a large difference between the constant current values, there is no influence of the offset and the error of the constant current value can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a heat detector 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 disconnection detection range of the thermistor of FIG. 1;

FIG. 4 is a timing chart showing control signals between the transmission processing MPU and the signal processing MPU of FIG. 1;

FIG. 5 is a flowchart for explaining the operation of the transmission processing MPU of FIG. 1;

FIG. 6 is a flowchart for explaining the operation of the signal processing MPU of FIG. 1;

FIG. 7 is a timing chart showing a current switching operation of the signal processing MPU of FIG. 1;

FIG. 8 is an explanatory diagram showing a switching operation of the switch in FIG. 2;

FIG. 9 is an explanatory diagram comparing the current switching speed between the embodiment and the conventional example.

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

[Explanation of symbols]

 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: Transistors R11 to R19: Resistance C: Capacitor

Claims (4)

(57) [Claims] In a heat sensor for detecting a fire by detecting an environmental temperature based on a voltage corresponding to a resistance value of a thermistor, a feedback voltage corresponding to an output current matches a constant input voltage. A constant current circuit having a differential amplifier that drives the output stage transistor unit at a constant current; a load resistor capable of switching a resistance value between power supply lines; an output stage transistor unit of the constant current circuit and the thermistor in series; A switching circuit for switching the resistance value of the load resistor so as to obtain a constant current value different for each detection temperature range in which the temperature can be detected in a linear resistance region of the thermistor. And heat detector. 2. The heat sensor according to claim 1, wherein an environmental temperature is detected by measuring a voltage across the thermistor. 3. The heat detector according to claim 1, wherein
The heat sensor, wherein the load resistor connects a plurality of resistors in series, and the switching circuit switches a resistance value of the load resistor by selectively short-circuiting the plurality of resistors. 4. The heat sensor according to claim 1, further comprising, when detecting a disconnection of the thermistor, a current having a further different value which can be detected in a linear resistance region where the characteristics of the thermistor stand. Control means for controlling the constant current circuit to apply the voltage to the thermistor, and determining whether or not the thermistor is disconnected based on a voltage corresponding to the resistance value of the thermistor in this state. vessel.