JP3046411B2 - Thermal analog sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as this type of thermal analog type sensor, for example, there is one shown in FIG. This thermal analog sensor comprises a heat detection element 50, an A / D conversion circuit 51, a CP
U52, a memory circuit 53, a temperature information output circuit 54, and a power supply circuit 55. An analog output signal from the heat detection element 50 is digitized by an A / D conversion circuit 51, and this digital signal is inputted to a CPU 52 and stored in a memory circuit in advance. 53
Is compared with the digital data at each temperature stored therein, and from the heat detection signal, it is determined how many temperatures the output signal indicates, 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 the thermal analog sensor. In other words, this thermal analog sensor outputs the temperature information of the alert area to the disaster prevention monitoring panel every moment, while the disaster prevention monitoring panel performs a fire prediction based on the received temperature information and gives an alarm before a fire occurs. in use.

[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 purpose, a platinum resistance thermometer having a linear temperature characteristic as a heat detecting element,
Since it is necessary to use a PN junction semiconductor, temperature IC, etc.,
The heat detection elements themselves become expensive, and since these elements have very small output signals, an amplifier circuit with a very high amplification factor is required, which raises the problem of increasing the overall cost. Was. A thermistor is an inexpensive heat detecting element, but the temperature characteristic is non-linear and cannot be used because it does not meet the conditions described above. FIG.
FIG. 7 shows a circuit in which a conventional thermistor 60 and a resistor 61 are connected in series, and FIG. 7 shows a temperature characteristic of the circuit. As can be seen from the figure, non-linearity in which the output change rate is small in the low temperature range and the high temperature range appears. Therefore, if the output of the thermistor is digitized by the A / D converter while keeping this characteristic, the resolution is deteriorated in a high / low temperature range. That is, several 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, the resolution is improved by using an A / D converter having a large number of bits, but the cost becomes extremely high. The present invention has been made in order to solve the conventional problems as described above, and it is possible to obtain high accuracy and uniform high resolution over the entire detection temperature range which is a condition of fire prediction, and at a low cost. It is an object of the present invention to provide a thermal analog sensor.

[0004]

Means for Solving the Problems The present invention according to claim 1 to solve the above problems, the analog signals from the thermal detection element is converted into a digital signal, and the temperature analyzed by the CPU on the basis of the digital signal In a thermal analog type sensor that outputs temperature information, a low-temperature signal equal to or less than a predetermined value is subtracted from the analog signal from the heat detecting element, and the remaining signal is amplified and output to a signal having good linear temperature characteristics. And a differential amplifying means. The thermal analog sensor according to the second aspect includes a differential amplifying unit that divides the temperature detection range into a plurality of parts, subtracts an unnecessary low-temperature range signal for each of the plurality of temperature detection ranges, and amplifies the signals at different amplification factors. It is characterized by the following. The thermal analog type sensor according to claim 3 is a thermal detection element.
Constant power supply from the power supply circuit to the heat detection unit including
The heat detector is intermittently activated by intermittent
Intermittently driving means for driving the motor.

[0005]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a thermal analog sensor according to an embodiment of the present invention. The thermal analog sensor is a power supply circuit 1 that supplies power to the entire circuit.
An intermittent drive circuit 2 for intermittently driving the circuit at fixed time intervals, a heat detection unit 3 for detecting a temperature and outputting an analog signal of a voltage value corresponding to the temperature, and a heat detection unit 3. A differential amplifier circuit for processing and amplifying analog signals 4,
5, 6 and an A / D converter 7 for converting analog outputs from the differential amplifier circuits 4, 5, 6 into digital signals;
CPU 8 for performing temperature analysis based on the digital signal from converter 7, memory circuit 9 for storing the correspondence between the temperature and the value of the digital signal as data, and outputting the temperature information from CPU 8 to a disaster prevention monitor panel or the like. And a temperature information output circuit 10.

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

FIG. 2 shows a detailed circuit configuration of the heat detecting section 3 and the differential amplifier circuits 4, 5, and 6. The heat detecting section 3 includes a thermistor 30 as a heat detecting element as shown in FIG.
1 and resistors R5, R6, 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 amplifiers 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 a voltage VTH. Voltage VTH
Is given by the formula: VTH = {R7 / (RTH + R7)} VDD. Here, RTH is thermistor 3
The internal resistance of 0, VDD is the voltage of the power supply circuit 1. This voltage VTH is applied to the operational amplifiers 4 of the differential amplifier circuits 4, 5, and 6.
0 is input to the non-inverting input.

The differential amplifier circuits 4, 5, and 6 are composed of operational amplifiers 40 and 41, respectively, and resistors R1 to R4. FIG. 2 shows only the circuit configuration of the differential amplifier circuit 4, but the differential amplifier circuits 5 and 6 have exactly the same configuration. In the present embodiment, the detection temperature range, which is a condition for fire prediction, is set to -30 to 80 ° C, and this detection temperature range is set to a low temperature range (-30 to 0 ° C) and a medium temperature range (0 to 40 ° C).
C.) and a high temperature range (40 to 80 ° C.), and signal processing in each temperature range is performed by the differential amplifier circuits 4, 5, and 6, respectively. The voltages set by the resistors R3 and R4 are input to the operational amplifier 41 and impedance-converted. The operational amplifiers 41 of the differential amplifier circuits 4, 5 and 6 output voltages Vref1, Vref2 and Vref3, respectively. Vref2 and Vref3 are input to the inverting input of the operational amplifier 40. The voltage Vref1 (2,3) is given by the following equation: Vref1 (2,3) = {R4 / (R3 + R4)} VDD. In addition, each of the differential amplifier circuits 4, 5,
In the operational amplifier 40 of No. 6, the voltage VTH and the voltage Vref 1 (2,
3) The amplified value of the difference is output as Vout1, Vout2, and Vout3. This Vout1 (2,3) is given by the following equation: Vout1 (2,3) = {(R1 + R2) R6 / (R5 + R6) R1} VTH- (R2 / R1) Vref1 (2,3)

The resistance value of the resistors R3 and R4 is changed for each of the differential amplifier circuits 4, 5, and 6 so that Vref1 (2,3) is set to a different value. A signal corresponding to the following temperature range is converted into 0 ° C.
In the differential amplifier circuit 6, signals corresponding to the following temperature ranges are
The signal corresponding to the temperature range of 40 ° C. or less is set to be cut. Further, by changing the resistance values of the resistors R1 and R2 for each of the differential amplifier circuits 4, 5 and 6, different amplification factors are set to correct the output in each temperature range as shown by the dotted line in FIG. The temperature characteristics as shown in FIG. That is, low temperature range (-30 to 0 ° C)
As shown in FIG. 7, the output change rate in the high temperature range (40 to 80 ° C.) is smaller than that in the middle temperature range (0 to 40 ° C.), so that the output change rate is almost the same as that in the middle temperature range. The rate is set. This enables high-resolution detection over the entire detection temperature range. Further, in each of the differential amplifier circuits 4, 5, and 6, for a signal corresponding to a temperature equal to or higher than the temperature range in charge, a constant saturated voltage value (= VDD) as shown in FIG. Vout2, Vout3
Is output.

Next, the operation of the thermal analog type sensor configured as described above will be described. The heat detector 3 outputs an analog signal of the voltage VTH corresponding to the ambient temperature. This voltage VTH follows the temperature characteristic shown in FIG. Voltage VTH
Are input to differential amplifier circuits 4, 5, and 6, respectively, and are subjected to signal processing according to the characteristics shown in FIG. For example, when the voltage VTH is a value corresponding to −10 ° C. in a low temperature range,
Vout1 is output after being amplified by the differential amplifier circuit 4.
In this case, since -10 ° C. is equal to or lower than the temperature range of the differential amplifier circuits 5 and 6, the signal is not amplified by the differential amplifier circuits 5 and 6 and Vout
2 and Vout3 both become 0. When the voltage VTH has a value corresponding to the medium temperature range of 20 ° C., the voltage is amplified by the differential amplifier circuit 5 and Vout2 is output. The differential amplifier circuit 4 outputs Vout1 of a saturated voltage value (= VDD) because the temperature exceeds the low temperature range.
out3 becomes 0. Similarly, when the voltage VTH is a value corresponding to 50 ° C. in a high temperature region, the differential amplifier circuits 4 and 5 output saturated voltage values (= VDD) Vout 1 and Vout 2, and the differential amplifier circuit 6 amplifies the voltage. The output Vout3 is output.

Outputs Vout1, Vout of 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 a saturation voltage value (= VDD) are digitized and input to PU8. The CPU 8 determines which of the differential amplifier circuits the digital signal is from, and compares the digital signal with data indicating the correspondence between the temperature and the digital signal stored in the memory circuit 9 in advance. 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 or the like to which a thermal analog sensor is connected.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments. For example, the intermittent drive circuit 2 does not always need to be provided unless reduction in current consumption is considered. In the above embodiment, since the temperature detection range is set wide from -30 to 80 ° C., the temperature range is divided into low, middle, 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, four or more differential amplifier circuits may be provided in a wider case. In the embodiment, A / D
Although 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 terminal is shown,
The A / D converter 7 has one input, and the differential amplifier circuit and A
A configuration in which a multiplexer circuit is added between the / D converters 7 may be employed. The heat detecting element is not limited to the thermistor 30, but may be a platinum resistance thermometer, a PN junction semiconductor, a temperature IC, or the like having good linearity. However, a corresponding amplifier circuit is required. The A / D converter 7, the CPU 8, the memory circuit 9
May be independent components, or may be a component obtained by packaging them in one package.

[0013]

As described above, according to the present invention, a low-temperature signal equal to or less than a predetermined value is subtracted from the analog signal from the heat detecting element, and the remaining signal is amplified to a signal having a temperature characteristic with good linearity. With the provision of the differential amplifying means for outputting the same, high-precision and uniform temperature accuracy and uniform high-resolution can be obtained. In addition, the heat detection element can be provided at a low cost because the temperature characteristic is non-linear and inexpensive, and there is no need to use expensive A / D converters and amplifiers. is there. According to the second aspect of the present invention, there is provided differential amplification means for dividing the temperature detection range into a plurality of parts, subtracting unnecessary low-temperature range signals for each of the plurality of temperature detection ranges, and amplifying the signals at different amplification factors. Thereby, higher temperature accuracy and higher 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 power detection circuit including the heat detection element is supplied from the power supply circuit.
By interrupting the power supply at regular intervals, the heat
The provision of the intermittent driving means for intermittently driving the detection section makes it possible to reduce current consumption.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating 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 heat detection unit and a differential amplifier circuit of the thermal analog sensor according to one embodiment of the present invention.

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

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

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

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

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

[Explanation of symbols]

 2 Intermittent drive circuit 3 Heat detection unit 4, 5, 6 Differential amplifier circuit 7 A / D converter 8 CPU 9 Memory circuit 30 Thermistor 40, 41 Operational amplifier

Claims (3)

(57) [Claims] 1. A thermal analog sensor which converts an analog signal from a heat detecting element into a digital signal, analyzes the temperature with a CPU based on the digital signal, and outputs temperature information. A thermal analog sensor comprising a differential amplifying means for subtracting a low-temperature region signal equal to or less than a predetermined value, amplifying the remaining signal into a signal having a temperature characteristic with good linearity, and outputting the amplified signal. 2. The apparatus according to claim 1, further comprising: a differential amplifying unit that divides the temperature detection range into a plurality of parts, subtracts an unnecessary low-temperature range signal for each of the plurality of temperature detection ranges, and amplifies the signals with different amplification factors. Item 4. A thermal analog sensor according to Item 1. 3. A heat detecting section including the heat detecting element.
Interrupting the power supply from the power supply circuit at regular intervals
The thermal analog sensor according to claim 1, further comprising an intermittent driving unit for intermittently driving the heat detecting unit.