JPH0543039U - Resistance temperature sensor temperature detection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To control and suppress the self-heating of the resistance temperature sensor to improve the accuracy of temperature detection and stabilize it. [Configuration] The signal output from the intermittent voltage generator 30 is turned on.
The time is shorter than the OFF time, and the ON time is shorter than the self-heating time of the resistance temperature sensor 10. During the ON time, an intermittent voltage of a predetermined cycle is used as a bias voltage for the resistance temperature sensor 10 and the resistance-voltage conversion unit 20. Apply. When the bias voltage is ON, the resistance-voltage conversion unit 20 outputs a signal when the effect of self-heating of the resistance temperature sensor 10 is small to the signal conversion unit 40 as a voltage, and does not output it when the bias voltage is OFF. The signal conversion unit 40 performs signal processing by synchronizing the output of the resistance-voltage conversion unit 20 with the voltage generation cycle of the intermittent voltage generation unit 30 and outputs it as a signal according to temperature.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

This invention is a temperature sensor [for example, NTC thermistors (N egative T emperature C oefficient Thermistor ) and platinum resistance, etc.] to detect a change in temperature as a change in voltage (electric resistance) by suppressing self-heating of the temperature The present invention relates to a temperature detection circuit that contributes to improvement of detection accuracy and stabilization thereof.

[0002]

[Prior Art]

 In general, as a method of converting temperature to voltage and extracting it, a resistor R (t) is used on one side of the bridge circuit and the change of resistance R (t) due to temperature change is extracted as change of V (0). (FIG. 6), or a method (FIG. 7) is known in which a constant current I (0) is passed through the resistor R (t) and the voltage is taken out from the terminal as the number 1.

[Equation 1]

[0003]

[Problems to be solved by the device]

 (Background of the Invention) The resistance-temperature characteristic of the NTC thermistor, which is a temperature sensor, has a resistance value Th (0) at the reference temperature T (0) and a resistance value Th (0) when the temperature changes to T (T). If T), then it is generally expressed by Equation 2.

[Equation 2] Here, B is a constant determined by the material of the NTC thermistor. Therefore, the temperature characteristic of the thermistor resistance shows a negative temperature characteristic that decreases exponentially as the temperature goes from low to high, and the linearity is very poor. The temperature characteristic of the resistance is improved and the linearity is much better.

By the way, when the temperature is detected using the thermistor, it is necessary to detect a minute resistance change as a voltage change according to the temperature. Since a DC output of voltage is usually obtained, amplification is performed using a DC amplifier. When an operational amplifier is used as a DC amplifier, the characteristic of this operational amplifier is that even if the input is 0V, a slight DC voltage is output (offset voltage). Also, the offset voltage increases as the amplification factor increases. Therefore, in order to make the offset voltage zero, a compensation circuit is required. Further, the offset voltage has a characteristic that it changes with temperature (temperature drift), and this influence is likely to cause an error in a circuit that measures temperature. Thus, it is necessary to determine the configuration of the entire temperature detection (measurement) circuit in consideration of the error component from the amplifier.

If a bridge circuit as shown in FIG. 5 is used in order to extract the resistance value according to the temperature change as a voltage change, the output E (out) from this bridge circuit can be obtained by the equation 3.

[Equation 3] In this case, in order to detect the resistance change of the temperature sensor with high accuracy, it is preferable to increase the bias current as much as possible to enhance the sensitivity. By increasing the bias voltage Eb applied to the bridge circuit, the output E (out ) Needs to be high. However, since the thermistor is a resistor, Joule heat is generated by the bias current. This Joule heat P is obtained by the equation 4 when the resistance value of the thermistor when the current I is passed is Th (P).

[Equation 4] This Joule heat causes a problem of so-called self-heating, in which the element itself generates heat. Self-heating is a temperature rise due to Joule heat as described above, and the time until it reaches a thermal equilibrium state depends on the structure of the element. It is remarkable. Therefore, in order to reduce the error caused by self-heating, a method is used in which the amount of self-heating is determined and the bias voltage and bias current applied to the device are determined from the accuracy required for measurement.

(Problems of Prior Art) When a thermistor is used as the temperature sensor, the problem of self-heating occurs as described above. For this reason, if the current is increased to improve the sensitivity, the resistance change due to the effect of self-heating increases and the measurement accuracy cannot be improved; NTC thermistors have a negative temperature coefficient of resistivity and self-heating. When the resistance of the element decreases due to this, a large current flows, but in such a case, the output signal E (out) becomes unstable due to the increase of the current, and when the heat storage amount exceeds the heat radiation amount, the element On the contrary, if the current is reduced to suppress self-heating, the output signal E (out) decreases and the measurement accuracy deteriorates; the time to reach the thermal equilibrium state is shortened, In order to stabilize the output, the structure of the device itself must be changed; and so on.

(Object of the Invention) Accordingly, an object of the present invention is to provide a temperature detection circuit that controls and suppresses self-heating of a resistance temperature sensor, improves the accuracy of temperature detection, and stabilizes it. .. Another object of the present invention is to provide a highly versatile temperature detection circuit that contributes to improving the reliability of the resistance temperature sensor and can be used for temperature sensors having different structures.

[0008]

[Means for Solving the Problems]

 The present invention converts a resistance value of a resistance temperature sensor, which is connected to the resistance temperature sensor and has a resistance element that changes its electric resistance according to a temperature change and that changes according to a temperature change, into a voltage value. Connected to the resistance-voltage conversion unit to be taken out and the resistance-voltage conversion unit, the ON time is shorter than the OFF time, and the ON time is from when the resistance temperature sensor starts self-heating to when it reaches a certain temperature. The intermittent voltage generator that repeats ON / OFF of a predetermined cycle in a shorter time than the time, and performs signal processing in synchronization with a predetermined cycle of ON / OFF of the voltage generated by the intermittent voltage generator to perform the resistance-voltage conversion. 3 is a temperature detection circuit of a resistance temperature sensor including a signal conversion unit that converts an output voltage of the unit into a signal according to temperature. A bridge circuit is configured by the resistance temperature sensor and the resistance-voltage converter, and the intermittent voltage generator applies a bias voltage to the bridge circuit at a predetermined cycle, and a constant voltage power supply. It is preferable to include a switch means for connecting the bridge circuit, and a pulse signal generating section for opening and closing the switch means with a pulse signal having a constant cycle and outputting a pulse signal to the signal converting section.

[0009]

[Work]

 For the signal output from the intermittent voltage generator, the ON time is shorter than the OFF time, and the ON time is shorter than the self-heating time of the resistance temperature sensor. Is applied to the resistance temperature sensor and the resistance-voltage converter. When the bias voltage is ON, the resistance-voltage converter outputs a signal to the signal converter when the effect of self-heating of the resistance temperature sensor is small, and does not output it when the bias voltage is OFF. The signal conversion unit performs signal processing by synchronizing the output of the resistance-voltage conversion unit with the voltage generation cycle of the intermittent voltage generation unit, and outputs a signal according to the temperature.

Prior to the description of the embodiments, the principle of the present invention will be described first. As shown in FIG. 1, the temperature detection circuit 1 includes a resistance temperature sensor 10 whose electric resistance changes due to a temperature change, a resistance-voltage conversion unit 20 including a resistance element and connected to the resistance temperature sensor 10, and a resistance-voltage conversion unit 20. The voltage conversion unit 20 includes an intermittent voltage generation unit 30 and a signal conversion unit 40. Among them, the resistance-voltage conversion unit 20 converts the resistance value of the resistance temperature sensor 10 which changes due to temperature change into a voltage value and takes it out. The ON / OFF time of the signal output from the intermittent voltage generating unit 30 is shorter than the OFF time, and the ON time is shorter than the time from when the resistance temperature sensor 10 starts self-heating to when it reaches a constant temperature. Repeated ON and OFF of a predetermined cycle depending on time. The resistance temperature sensor 10 is connected to the resistance-voltage converter 20 to form a bridge circuit, and the intermittent voltage generator 30 is connected to the bridge circuit to supply a bias voltage to the bridge circuit at regular intervals. The signal conversion unit 40 performs signal processing in synchronization with the intermittent period of the voltage generated by the intermittent voltage generation unit 30, converts the output of the resistance-voltage conversion unit 20 into a signal corresponding to temperature, and outputs the signal. .. That is, the signal converter 40 synchronizes with the cycle in which the intermittent voltage generator 30 supplies the bias voltage at regular intervals, and converts the output signal of the bridge circuit into an output signal according to the temperature and outputs the output signal. FIG. 2 is a time chart regarding the intermittent voltage generated by the intermittent voltage generating unit 30 and the output of the resistance-voltage conversion unit 20 in a constant cycle. In FIG. 2, a shows an output waveform when the resistance value of the resistance temperature sensor is converted in an ideal state assuming that there is no self-heating at the temperature T. b shows the output voltage when the jule heat is generated immediately after the conventional bias voltage is applied. Immediately after the bias voltage is applied, jule heat is generated, and the temperature reaches an equilibrium state after a lapse of time t. In this way, the output voltage increases by Δe (V) as an error of the temperature increase due to Joule heat generation. Therefore, now, the bias voltage applied to the resistance-voltage conversion unit 20 is repeatedly turned on and off at constant time intervals generated by the intermittent voltage generation unit 30 so that the ON time Δt is shorter than the OFF time Δx and the ON time is longer. Let .DELTA.t be an intermittent voltage that is sufficiently shorter than the self-heating time t of the resistance temperature sensor. Then, the output waveform C of the resistance-voltage conversion unit 20 becomes the output waveform C in FIG. 2 due to the intermittent voltage generated in the intermittent voltage generation unit 30. The waveform C outputs the resistance value of the resistance temperature sensor 10 when there is almost no influence of Joule heat as a voltage value, and radiates the heat component heated by itself when the bias voltage is OFF. Therefore, if the ON time Δt in FIG. 2 is sufficiently shortened, the output at ON approaches the ideal output E (V) because the self-heating amount of the resistance temperature sensor becomes small.

Next, the present invention will be described in detail with reference to the drawings regarding a preferred embodiment thereof. FIG. 3 is a block diagram showing the basic configuration of the present invention. In this figure, reference numeral 1 is a temperature detection circuit, 10 is a resistance temperature sensor whose electric resistance changes with temperature change, and 20 is composed of three resistance elements R (1), R (2) and R (3). And a resistance-voltage converter. The resistance temperature sensor 10 is connected to the resistance-voltage converter 20 to form a bridge circuit 50. Reference numeral 30 denotes an intermittent voltage generating unit, which applies a bias voltage to the bridge circuit 50 composed of the resistance temperature sensor 10 and the resistance-voltage conversion unit 20 at a predetermined cycle. Reference numeral 40 denotes a signal conversion unit that performs signal conversion in synchronization with the intermittent period of the intermittent voltage generated by the intermittent voltage generating unit 30. Reference numeral 35 is a constant voltage power source for applying a bias voltage to the bridge circuit 50, 36 is a switch means for connecting the constant voltage power source 35 and the bridge circuit 50, and 37 is a switch for generating a pulse signal of a constant cycle, It is a pulse signal generator that opens and closes (ON / OFF) the means 36 with a pulse signal and outputs the pulse signal to the signal converter 40. 41 is an amplifier and 42 is a sample and hold circuit. Here, the operation of this embodiment will be described with reference to the time chart of FIG. In FIG. 4, αa represents an output signal in an ideal state in which it is assumed that the resistance temperature sensor 10 does not self-heat even if a bias voltage is continuously applied (where α is the amplification factor of the amplifier 41). .. αb represents an output signal when the bias voltage is continuously applied to the bridge circuit 50, and αc represents a signal obtained by amplifying the output from the bridge circuit 50 when the bias voltage is intermittently applied. The pulse signal generated by the pulse generator 37 repeats ON / OFF at regular time intervals, and the ON time is shorter than the OFF time and shorter than the self-heating time of the resistance temperature sensor 10. When the pulse signal is turned on, the switch means 36 connects the constant voltage power source 35 to the bridge circuit 50. Then, a bias voltage is applied to the bridge circuit 50 from the constant voltage power supply 35, the resistance value corresponding to the temperature of the resistance temperature sensor 10 is converted into a voltage value, and the output c is output (see FIG. 3). When the output c is amplified by the amplifier 41 of the signal conversion unit 40, the signal waveform at this time becomes αc. αc has the same rise as αb, but the output becomes 0 because the bias voltage is turned off long before the temperature rise due to self-heating of the resistance temperature sensor 10 reaches an equilibrium state. Therefore, the signal αc is input to the sample hold circuit 42. The sample hold circuit 42 samples and holds αc in synchronization with the pulse of the pulse signal generator 37. In this way, the sample-held signal is output as the output V of the signal conversion unit 40. After that, the signal conversion is repeated in synchronization with the pulse signal generated by the pulse signal generator 37. Thus, the output V of the signal conversion unit 40 approaches the ideal output αa (error due to self-heating is suppressed, and an output having a value close to the ideal output signal is obtained).

[0012]

[Effect of the device]

 Since the present invention is configured as described above, it has the following effects. When a thermistor is used as a temperature sensor, the temperature detection circuit can control and suppress the self-heating of the element by using a thermistor whose temperature resistance coefficient is known. Stabilization can be realized. Further, since the resistance temperature sensor can be applied to resistance temperature sensors having different structures, a temperature detection circuit of the resistance temperature sensor having high versatility can be obtained. In addition, since the output signal of the temperature sensor forming the temperature detector can be output as a waveform including a time component, AC amplification can be performed. Moreover, since the direct current component can be cut, it is possible to eliminate the influence of offset voltage and the like during signal processing.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the principle of the present invention.

FIG. 2 is a time chart explaining the operation principle of the present invention shown in FIG.

FIG. 3 is a configuration block diagram showing an embodiment of a temperature detection circuit according to the present invention.

FIG. 4 is a time chart for explaining the operation of the embodiment of the present invention.

FIG. 5 is a circuit diagram of a bridge circuit using a thermistor.

FIG. 6 is a circuit diagram showing a method of converting the temperature of a resistance element into a voltage and extracting the voltage.

FIG. 7 is a circuit diagram showing another method of converting the temperature of the resistance element into a voltage and extracting the voltage.

[Explanation of symbols]

 1 Temperature Detection Circuit 10 Resistance Temperature Sensor 20 Resistance-Temperature Converter 30 Intermittent Voltage Generator 35 Constant Voltage Power Supply 36 Switch Means 37 Pulse Signal Generator 40 Signal Converter 41 Amplifier 42 Sample Hold Circuit

Claims (2)

[Scope of utility model registration request] 1. A resistance temperature sensor (10) whose electric resistance changes according to a temperature change, and a resistance temperature sensor (1) provided with a resistance element and connected to the resistance temperature sensor (10) which changes according to a temperature change.
0) is connected to the resistance-voltage conversion unit (20) for converting the resistance value of the voltage value into a voltage value, and the resistance-voltage conversion unit (20).
ON / OFF of a predetermined cycle is shorter than the FF time and shorter than the time from when the resistance temperature sensor (10) starts self-heating to when the resistance temperature settles down to a constant temperature.
And a resistance-voltage conversion unit (20) that performs signal processing in synchronization with the intermittent period of the voltage generated by the intermittent voltage generation unit (30).
A temperature detection circuit for a resistance temperature sensor, comprising a signal conversion unit (40) for converting the output of the above into a signal corresponding to temperature and outputting the signal. 2. A resistance temperature sensor (10) whose electric resistance changes according to temperature change, and a resistance temperature sensor (1) provided with a resistance element and connected to the resistance temperature sensor (10) which changes according to temperature change.
0) is connected to the resistance-voltage conversion unit (20) for converting the resistance value of the voltage value into a voltage value, and the resistance-voltage conversion unit (20).
ON / OFF of a predetermined cycle is shorter than the FF time and shorter than the time from when the resistance temperature sensor (10) starts self-heating to when the resistance temperature settles down to a constant temperature.
And a resistance-voltage conversion unit (20) that performs signal processing in synchronism with the intermittent period of the voltage generated by the intermittent voltage generation unit (30).
A resistance conversion sensor (10) and a resistance-voltage conversion unit (20) to form a bridge circuit (50). Then, the intermittent voltage generating unit (30) causes the bridge circuit (5
0) a constant voltage power source (35) for applying a bias voltage at a predetermined cycle, a switch means (36) connecting the constant voltage power source (35) and the bridge circuit (50), and the switch means (36). A temperature detecting circuit for a resistance temperature sensor, comprising a pulse signal generator (37) for opening and closing with a pulse signal of a constant cycle and outputting the pulse signal to the signal converter (40).