JPH0528376A - Thermal analog sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a thermal analog type sensor that can obtain high precision and uniform high resolution over the entire detection temperature range that is a condition for fire prediction, and is inexpensive. In a thermal analog sensor for converting an analog signal from the heat detecting element 30 into a digital signal and analyzing the temperature with a CPU based on the digital signal and outputting temperature information, a predetermined analog signal from the heat detecting element 30 is output. Differential amplification means 4 for subtracting the following low temperature range signals, amplifying the remaining signals into signals having temperature characteristics with good linearity, and outputting the signals.
Equipped with 5 and 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal analog sensor for transmitting temperature information in a warning zone for fire forecasting.

[0002]

2. Description of the Related Art Conventionally, as a thermal analog type sensor of this type, there is one shown in FIG. 5, for example. This thermal analog type sensor includes a thermal detection element 50, an A / D conversion circuit 51, a CP.
A U52, a memory circuit 53, a temperature information output circuit 54, and a power supply circuit 55. The analog output signal from the heat detecting element 50 is digitized by the A / D conversion circuit 51, and this digital signal is input to the CPU 52 to be stored in advance in the memory circuit. 53
The temperature information signal is compared with the digital data stored at each temperature to determine how many temperatures the output signal indicates from the heat detection signal, and the temperature information signal is output via the temperature information output circuit 54. This is output to the disaster prevention monitoring panel connected to this thermal analog sensor. In other words, this thermal analog type sensor outputs the temperature information of the warning area to the disaster prevention monitoring panel moment by moment, while the disaster prevention monitoring panel side predicts the fire from the received temperature information and warns before a fire occurs. It is used.

[0003]

However, in the conventional thermal analog type sensor as described above, the fire prediction requires high accuracy and uniform temperature accuracy and high resolution over the entire detection temperature range. It had been. For this reason, a platinum resistance thermometer having a linear temperature characteristic as a heat detecting element,
Since it is necessary to use a PN junction semiconductor, a temperature IC, etc.,
There is a problem in that the thermal detection element itself becomes expensive, and because the output signal of these elements is very small, an amplifier circuit with a very large amplification factor is required, which increases the overall cost. It was Further, although a thermistor is available as an inexpensive heat detecting element, the temperature characteristic is non-linear and cannot be used because it does not meet the conditions described above. Figure 6
Shows a circuit when a conventional thermistor 60 and a resistor 61 are connected in series, and FIG. 7 shows the temperature characteristics of the circuit. As can be seen from the figure, the output change rate shows a small nonlinearity in the low temperature region and the high temperature region. Therefore, if the output of the thermistor is digitized by the A / D converter with this characteristic, the resolution becomes poor in the high and low temperature range. In other words, it is possible that a few bits / ° C. can be obtained in the medium temperature range, but less than 1 bit / ° C. in the high / low temperature range. For these reasons, there is a problem in using a thermistor as a heat detecting element. Further, even when a thermistor is used as the heat detecting element, if the A / D converter having a large number of bits is used, the resolution is improved, but the cost becomes very high. The present invention has been made in order to solve the above conventional problems, and is capable of obtaining highly accurate and uniform high resolution over the entire detection temperature range, which is a condition for fire prediction, and is inexpensive. The present invention aims to provide a thermal analog sensor.

[0004]

In order to solve the above-mentioned problems, the present invention according to claim 1 converts an analog signal from a heat detecting element into a digital signal, and the CPU analyzes the temperature based on the digital signal to obtain temperature information. In a thermal analog sensor that outputs a difference between the analog signal from the heat detection element, a low temperature region signal below a predetermined value is subtracted, and the remaining signal is amplified to a signal having a temperature characteristic with good linearity and output. It is characterized in that a dynamic amplification means is provided. The thermal analog sensor according to claim 2 is provided with a differential amplifying means for dividing the temperature detection range into a plurality of parts, subtracting an unnecessary low temperature region signal for each of the plurality of temperature detection ranges, and amplifying with a different amplification factor. It is characterized by A thermal analog sensor according to a third aspect of the present invention is characterized by including intermittent driving means for intermittently driving by intermittently supplying power to the sensor.

[0005]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a thermal analog sensor according to an embodiment of the present invention. This thermal analog sensor is a power supply circuit 1 that supplies power to the entire circuit.
An intermittent drive circuit 2 that drives the circuit intermittently at regular time intervals; a heat detection unit 3 that detects temperature and outputs an analog signal of a voltage value corresponding to the temperature; Differential amplifier circuit 4, which processes and amplifies analog signals
5, 6 and an A / D converter 7 for converting the analog output from the differential amplifier circuits 4, 5, 6 into a digital signal, and an A / D
A CPU 8 that performs temperature analysis based on the digital signal from the converter 7, a memory circuit 9 that stores the correspondence relationship between the temperature and the value of the digital signal as data, and temperature information from the CPU 8 is output to a disaster prevention monitoring panel or the like. It is composed of a temperature information output circuit 10.

The intermittent drive circuit 2 intermittently performs the heat detection operation of the thermal analog type sensor by intermittently supplying power from the power supply circuit 1 at regular intervals. A contact type switching circuit or the like is used. By performing intermittent operation by the intermittent drive circuit 2, the average current consumption can be suppressed to be small.

FIG. 2 shows a detailed circuit configuration of the heat detector 3 and the differential amplifier circuits 4, 5 and 6. The heat detection unit 3 includes a thermistor 30 as a heat detection element and an operational amplifier 3 as shown in the figure.
1 and resistors R5, R6 and R7. The connection point of the series circuit of the thermistor 30 and the resistor R7 is connected to the input of the operational amplifier 31, and the output of the operational amplifier 31 is input to the differential amplifier circuits 4, 5 and 6 via the resistor R5. The output of the thermistor 30 is impedance-converted by the operational amplifier 31 and output as the voltage VTH. Voltage VTH
Is given by the equation: VTH = {R7 / (RTH + R7)} VDD. Where RTH is the thermistor 3
The internal resistance of 0, VDD, is the voltage of the power supply circuit 1. This voltage VTH is the operational amplifier 4 of each differential amplifier circuit 4, 5, 6.
Input to the non-inverting input of 0.

The differential amplifier circuits 4, 5 and 6 are composed of operational amplifiers 40 and 41 and resistors R1 to R4, respectively. In FIG. 2, only the circuit configuration of the differential amplifier circuit 4 is shown, but the differential amplifier circuits 5 and 6 have exactly the same configuration. In the present embodiment, the detection temperature range that is the condition for fire prediction is set to -30 to 80 ° C, and this detection temperature range is set to the low temperature range (-30 to 0 ° C) and the medium temperature range (0 to 40).
C.) and a high temperature region (40 to 80.degree. C.), and the differential amplifier circuits 4, 5 and 6 respectively perform signal processing in each temperature region. The voltages set by the resistors R3 and R4 are input to the operational amplifier 41 and impedance-converted, and the voltages Vref1, Vref2 and Vref3 are output from the operational amplifier 41 of each differential amplifier circuit 4, 5 and 6, respectively. Vref2 and Vref3 are input to the inverting input of the operational amplifier 40. The voltage Vref 1 (2,3) is given by the expression Vref 1 (2,3) = {R4 / (R3 + R4)} VDD. In addition, each differential amplifier circuit 4, 5,
In the operational amplifier 40 of 6, the voltage VTH and the voltage Vref 1 (2,
The values obtained by amplifying the difference of 3) are output as Vout1, Vout2, and Vout3. This Vout1 (2,3) is given by the equation: Vout1 (2,3) = {(R1 + R2) R6 / (R5 + R6) R1} VTH- (R2 / R1) Vref1 (2,3).

By changing the resistance values of the resistors R3 and R4 for each of the differential amplifier circuits 4, 5 and 6 to make Vref 1 (2, 3) different, the differential amplifier circuit 4 has a temperature of -30 ° C. In the differential amplifier circuit 5, the signal corresponding to the temperature range below is 0 ° C.
In the differential amplifier circuit 6, a signal corresponding to the following temperature range is
The signal corresponding to the temperature range of 40 ° C. or less is set to be cut. Further, different amplification factors are set by changing the resistance values of the resistors R1 and R2 for each of the differential amplifier circuits 4, 5 and 6, and the output in each temperature range is corrected as shown by the dotted line in FIG. The temperature characteristic as shown in 3 is obtained. That is, low temperature range (-30 to 0 ° C)
In the high temperature range (40 to 80 ° C), the output change rate is smaller than that in the middle temperature range (0 to 40 ° C) as shown in FIG. The rate is set. As a result, high resolution detection is possible in the entire detection temperature range. Further, in each of the differential amplifier circuits 4, 5 and 6, for a signal corresponding to a temperature above the assigned temperature range, as shown in FIG. 3, a constant saturated voltage value (= VDD) is Vout1, Vout2, Vout3
Is output as.

Next, the operation of the present thermal analog type sensor constructed as described above will be described. The heat detector 3 outputs an analog signal of the voltage VTH according to the ambient temperature. This voltage VTH follows the temperature characteristic shown in FIG. Voltage VTH
Signals are input to the differential amplifier circuits 4, 5 and 6, respectively, and signal processing is performed according to the characteristics shown in FIG. For example, when the voltage VTH has a value corresponding to −10 ° C. in the low temperature range,
Amplified by the differential amplifier circuit 4, Vout1 is output.
In this case, −10 ° C. is below the temperature range of the differential amplifier circuits 5 and 6, so that the differential amplifier circuits 5 and 6 do not amplify Vout.
2 and Vout3 are both 0. When the voltage VTH has a value corresponding to 20 ° C. in the middle temperature range, it is amplified by the differential amplifier circuit 5 and Vout2 is output. Since the differential amplifier circuit 4 exceeds the low temperature range, Vout1 of a saturated voltage value (= VDD) is output, and the differential amplifier circuit 6 is below the high temperature range, so Vout1
out3 becomes 0. Similarly, when the voltage VTH has a value corresponding to 50 ° C. in the high temperature range, the differential amplifier circuits 4 and 5 output saturated voltage values (= VDD) of Vout1 and Vout2, and the differential amplifier circuit 6 amplifies them. The output Vout3 is output.

Outputs Vout1, V of the differential amplifier circuits 4, 5, 6
out2 and Vout3 are digitized by the A / D converter 7 controlled by the CPU 8 and input to the CPU 8. C
Only outputs Vout1, Vout2, and Vout3 other than 0 or the saturation voltage value (= VDD) are digitized and input to PU8. The CPU 8 discriminates which differential amplifier circuit the digital signal is from, compares the digital signal with data stored in the memory circuit 9 in advance and showing the correspondence relationship between the temperature and the digital signal, and the heat detector 3 Analyze the detected temperature. Then, the CPU 8 transmits the analyzed temperature information via the temperature information output circuit 10 to, for example, a disaster prevention monitoring panel to which a thermal analog sensor is connected.

The present invention has been described above with reference to the preferred embodiments, but the present invention is not limited to the above embodiments. For example, the intermittent drive circuit 2 does not necessarily have to be provided unless the current consumption is reduced. In the above-mentioned embodiment, since the temperature detection range is set as wide as −30 to 80 ° C., the temperature range is divided into three, low, medium and high, and three differential amplifier circuits are provided correspondingly. 1 if the detection range is narrow
Alternatively, two differential amplifier circuits may be used, or conversely, if more wide, four or more circuits may be provided. In the embodiment, the A / D
The case where the converter 7 has a plurality of input terminals and the differential amplifier circuits 4, 5 and 6 are connected to the input terminals has been described.
The A / D converter 7 has one input, and the differential amplifier circuit and A
A multiplexer circuit may be added between the / D converters 7. The heat detecting element is not limited to the thermistor 30, but may be a platinum resistance temperature measuring element having a good linearity, a PN junction semiconductor, a temperature IC, or the like. However, a corresponding amplifier circuit is required. The A / D converter 7, the CPU 8, the memory circuit 9
May be independent parts or may be a single package of these parts.

[0013]

As described above, according to the present invention, a low temperature region signal below a predetermined level is subtracted from the analog signal from the heat detecting element, and the remaining signal is amplified into a signal having a temperature characteristic with good linearity. By providing the differential amplifying means for outputting in the same manner, it is possible to obtain highly accurate and uniform temperature accuracy and uniform high resolution. In addition, the thermal detection element is inexpensive and has a non-linear temperature characteristic, and since it is not necessary to use expensive A / D converters and amplifiers, it is possible to provide it at low cost. is there. According to the second aspect of the present invention, the temperature detection range is divided into a plurality of parts, and the unnecessary low-temperature range signal is subtracted for each of the plurality of temperature detection ranges, and the differential amplification means is provided for amplifying with different amplification factors. Thereby, more accurate temperature accuracy and high resolution can be obtained in a wide temperature range, and accurate temperature analysis can be performed. According to the third aspect of the present invention, the current consumption can be suppressed to a low level by providing the intermittent driving means for intermittently driving the power supply at regular intervals.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a thermal analog sensor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a thermal detection unit and a differential amplifier circuit of a thermal analog sensor according to an exemplary embodiment of the present invention.

FIG. 3 is a diagram showing temperature-voltage characteristics of a thermal analog sensor according to an embodiment of the present invention.

FIG. 4 is a diagram showing a correction state of a thermal analog sensor according to an embodiment of the present invention.

FIG. 5 is a block diagram showing the overall configuration of a conventional thermal analog sensor.

FIG. 6 is a circuit diagram showing an example of a circuit using a thermistor.

7 is a diagram showing temperature-voltage characteristics of the thermistor shown in FIG.

[Explanation of symbols]

2 intermittent drive circuit 3 Heat detector 4, 5, 6 differential amplifier circuit 7 A / D converter 8 CPU 9 Memory circuit 30 thermistor 40, 41 operational amplifier

Claims (3)

[Claims] 1. A thermal analog sensor for converting an analog signal from a heat detecting element into a digital signal, analyzing the temperature in a CPU based on the digital signal, and outputting temperature information. A thermal analog sensor characterized by comprising differential amplification means for subtracting a low temperature signal below a predetermined value and amplifying the remaining signal to a signal having temperature characteristics with good linearity and outputting the signal. 2. A differential amplification means for dividing the temperature detection range into a plurality of parts, subtracting an unnecessary low temperature region signal for each of the plurality of temperature detection ranges, and amplifying the signals at different amplification rates. Item 1. A thermal analog sensor according to item 1. 3. The power supply is intermittently supplied at regular intervals,
3. The thermal analog sensor according to claim 1, further comprising an intermittent driving means for performing intermittent driving.