JPH09105680A - Temperature measuring circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the effective resolution by cancelling the offset component of a temperature measuring resistor, and increasing the amplification factor of an amplifier of the next stage. SOLUTION: Since the current supplied from a second constant-current source 2 flows in a temperature measuring resistor R, when the resistance value of the resistor R is changed, the change becomes a voltage change, which is input to an operational amplifier 1. At the time of 0 deg.C, if the voltage drop generated at the resistor by the resistance value of the resistor R is cancelled by the voltage drop generated at a resistor R4, the voltage of 0V is input to the amplifier 1 at the time of 0 deg.C, the offset component is cancelled. Then, the resistance value of the resistor R at the time of 0 deg.C is set as the resistance value of the resistor R4, and the offset component is cancelled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature measuring circuit for obtaining an amplifier output voltage corresponding to temperature by using a resistance temperature detector as a temperature sensor.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing an example of a conventional temperature measuring circuit. In the figure, 1 is an operational amplifier for amplifying a voltage corresponding to a resistance change of a resistance temperature detector R, 2a, 2b.
Is the first and second constant current sources for supplying the current I to the resistance temperature detector R and the like, R2 and R3 are resistors for determining circuit constants such as setting the amplification factor of the operational amplifier 1, and r is a wiring resistance. .

Next, the operation will be described. RTD R
Has a resistance value that changes depending on the ambient temperature. Therefore,
When the resistance value changes, the voltage drop due to the resistance temperature detector R also changes, so that the second constant current source 2b is applied to the resistance temperature detector R.
From the above, a constant current I is supplied to convert a change in resistance into a change in voltage (R-V conversion), which is input to the operational amplifier 1. The operational amplifier 1 amplifies and outputs the voltage drop due to the resistance temperature detector R. Therefore, the output voltage of the operational amplifier 1 has a value corresponding to the temperature around the resistance temperature detector R.

Here, when the resistance value of the resistance temperature detector R changes with temperature as shown in FIG.
As a result of the −V conversion, a change in resistance becomes a change in voltage as shown in FIG. 6 (B), and this change in voltage is amplified by the operational amplifier 1 so that the temperature changes as shown in FIG. 6 (C). Will be output as a voltage corresponding to. The second
The current coming from the operational amplifier 1 is smaller than the current I supplied from the constant current source 2b in FIG.
>>> r, so that the wiring resistance r is regarded as 0 and the gain of the operational amplifier 1 is G, the output voltage V of the operational amplifier 1 is V.
0 is V0 = R × I × G.

By the way, as the temperature sensor, there is a thermocouple or the like in addition to the resistance temperature detector R used in FIG. FIG. 7 (A)
Is a characteristic diagram showing the relationship between the output voltage of the thermocouple and the temperature scale. At 0 ° C., the output voltage is 0 V, and the output voltage rises almost linearly as the temperature rises. The amplifier output voltage obtained by amplifying the output voltage of such a thermocouple with an operational amplifier or the like as in the above is shown in FIG.
As shown in (B), the output voltage is 0 at 0 ° C.
V, and its output voltage rises almost linearly as the temperature rises. In other words, the thermocouple has a large dynamic range (effective range) even if it is amplified, but the resistance thermometer sensor has an offset of 100Ω at 0 ° C. It is something that cannot be taken big.

However, when the resistance temperature detector R is used as the temperature sensor as shown in FIG. 1, there is an offset of 100Ω when the temperature is 0 ° C. as shown in FIG. Since the offset voltage is generated as shown in (B), the operational amplifier 1 has to amplify the resistance change of the resistance temperature detector R including the offset amount, so that the resistance change can be greatly amplified. As a result, the effective resolution (the ratio of the amplifier output range to the input temperature range or the change rate) becomes small.

FIG. 8 is a table comparing the input temperature range, the sensor output value, the amplifier output voltage, and the specific values of the rate of change when a thermocouple is used as the temperature sensor and when a resistance temperature detector is used. is there. In the example using the thermocouple, the amplification factor of the operational amplifier is 610.5 times (the amplification factor is 2.5 V at maximum input), but in the example using the resistance thermometer, The amplification factor of the amplifier is 17.9 times (the amplification factor is 2.5 V at maximum input, and the current supplied to the sensor is 1 mA).

After all, when a resistance temperature detector is used as the temperature sensor, its resistance is 100Ω even at 0 ° C., which is an offset component (a voltage drop caused by the current flowing in 100Ω). As is clear from the table diagram of FIG. 8, it is difficult to greatly amplify the sensor output by the operational amplifier 1 in the next stage and set a wide output voltage range. If a thermocouple is used as the temperature sensor, 0 ° C
At that time, since it is 0 V, the sensor output can be greatly amplified by the operational amplifier in the next stage, and the output voltage range can be widened.

FIG. 9 is a circuit diagram showing another example of a conventional temperature measuring circuit. In the figure, first and second constant voltage sources 3a and 3b are connected to the input side of an operational amplifier 1. . Other configurations are the same as those of the conventional example shown in FIG. 5, and the same parts are described by using the same reference numerals, and the description thereof will be omitted.

Next, the operation will be described. RTD R
The resistance value of the element changes depending on the ambient temperature as shown in FIG. In this case, since the first and second constant voltage sources 3a and 3b of Vref are connected to the input side of the operational amplifier 1, the current flowing through the resistance temperature detector R is Vref.
/ (R + R1). As a result, a non-linear voltage with respect to the temperature of R × Vref / (R + R1) as shown in FIG. 10B is input to the operational amplifier 1. When the gain of the operational amplifier 1 is G, the output voltage V0 of the operational amplifier 1 is
Becomes V0 = R × {Vref / (R + R1)} × G,
A non-linear output voltage with respect to temperature as shown in FIG. 10C is obtained. However, since the current from the operational amplifier 1 is smaller than the current supplied from the second constant voltage source 3b, this is ignored, and since R >> r, the wiring resistance r is regarded as 0. I ignored it.

In this case, the voltage change corresponding to the temperature change becomes non-linear as shown in FIGS. 10 (B) and (C), but the resistance change of the resistance temperature detector R becomes as shown in FIG. 10 (A). Since there is an offset, there is a problem that the sensor output cannot be greatly amplified by the operational amplifier 1 and the output voltage range cannot be widened as in the conventional example.

[0012]

Since the conventional temperature measuring circuit using the resistance temperature detector as the temperature sensor is configured as described above, the resistance temperature detector including the offset component of the resistance temperature detector R is measured. Since the output amount of the body R must be amplified by the operational amplifier 1 in the next stage, the amplification factor cannot be increased, the output voltage range becomes narrow, and the effective resolution becomes small. is there.

Therefore, the present invention has been made to solve the above-mentioned problems, and the offset component of the resistance temperature detector is artificially canceled to increase the amplification factor of the amplifier at the next stage. Therefore, it is an object of the present invention to obtain a temperature measurement circuit capable of increasing the effective resolution.

[0014]

According to a first aspect of the present invention, there is provided a temperature measuring circuit for supplying a current to a resistance temperature detector.
A second constant current source, a canceling resistor supplied with a current from the second constant current source so that a voltage drop occurs in a direction opposite to the voltage drop generated in the resistance temperature detector, and the resistance temperature detector. And an amplifier whose input voltage is an addition component of the voltage drop of the cancel resistor and the voltage drop of the canceling resistor.

In the temperature measuring circuit according to the second aspect of the present invention, the first and second constant voltage sources for applying a voltage to the resistance temperature detector and the current flowing in the direction opposite to the current flowing through the resistance temperature detector are provided. A canceling resistor that is supplied with a voltage from the second constant voltage source so as to flow, and an amplifier that uses an addition component of the voltage drop of the resistance temperature detector and the voltage drop of the canceling resistor as an input voltage. Be prepared.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. 1 is a diagram showing a configuration of a temperature measuring circuit according to a first embodiment of the present invention. In the figure, R is, for example, a three-wire resistance temperature detector, and R4 is an offset component of the resistance temperature detector R. This is a canceling resistor inserted on the input side of the operational amplifier 1 in order to do so. However, since the same parts as those in the conventional example are denoted by the same reference numerals, the description of the same parts will be omitted.

Next, the operation will be described. When the three-wire resistance temperature detector R is used, one line thereof is connected to the + side input line of the operational amplifier 1, and the other one line is connected to the-side input line of the operational amplifier 1. Furthermore, the remaining one line is connected to the ground potential of the circuit. The resistance value of the resistance temperature detector R connected in this way changes depending on the ambient temperature. The resistance temperature detector R is supplied from the constant current source 2b with the current I.
Is supplied, a reverse voltage drop occurs in the resistor R4. As a result, the sum of the voltage drop of the resistance temperature detector R and the voltage drop of the resistor R4 is input to the operational amplifier 1. The operational amplifier 1 amplifies the input voltage and outputs it. Since the current from the operational amplifier 1 is smaller than the current I supplied from the second constant current source 2b, it is ignored, and since R >> r and R4 >> r, the wiring resistance is If r is regarded as 0 and the gain of the operational amplifier 1 is G,
The output voltage of the operational amplifier 1 is V0 = (R−R4) × I × G.

The resistance temperature detector R used in this example also has an offset resistance value of about 100Ω at 0 ° C. Here, the value of the resistor R4 for canceling the offset voltage generated by the offset resistance value at 0 ° C. will be calculated here. As described above, the output voltage V0 of the operational amplifier 1 is V0 = (R−R4) × I × G. To cancel the offset voltage in a pseudo manner by preventing the offset voltage generated in the resistance temperature detector R from being input to the operational amplifier 1 at 0 ° C., at 0 ° C., V0 = (R−R4) × I ×
It is sufficient that G = 0, that is, R4 = R. To this end, the value of the canceling resistor R4 may be set to the resistance value that the resistance temperature detector R has when it is 0 ° C., and this allows the offset value that the resistance temperature detector R has when it is 0 ° C. Will be canceled in a pseudo manner when R-V conversion is performed. In the first embodiment, the input temperature range of the resistance temperature detector is 0 ° C to 100 ° C.

FIG. 2 shows an example of resistance characteristics with respect to temperature of the resistance temperature detector R according to the first embodiment, an example of voltage characteristics with respect to temperature when a change in the resistance value of the resistance temperature detector R is converted into a voltage, and the operational amplifier 1. FIG. 5 is a diagram showing an example of output voltage characteristics with respect to temperature. As shown in FIG. 2A, the resistance temperature detector R of this example is also 0 ° C.
At that time, there is an offset of 100Ω, and the resistance value linearly increases as the temperature rises. FIG. 2B shows a characteristic obtained by RV converting the change in the resistance value of the resistance temperature detector R. In this case, since the canceling resistor R4 is selected to be 100Ω as described above, the voltage becomes 0 mV at 0 ° C., and the voltage increases almost linearly as the temperature rises.
It can be seen that the offset voltage has been canceled.
For this reason, the amplifier output voltage of the operational amplifier 1 also has no offset voltage, and the output voltage increases almost linearly at 0V at 0V with increasing temperature.

As is apparent from comparison between the characteristic diagram of FIG. 2C and the conventional characteristic diagram of FIG. 6C, the voltage value of the final range width is 4V (= 14V-10V) in the conventional case, and in this example. 1
At 4V (14V-0V), it is possible to improve the range width three times or more.

According to this embodiment, the resistance temperature detector R is zero.
The offset resistance at the time of ℃
Since the voltage can be pseudo canceled at the time of the R-V conversion by 4, the voltage that has no offset amount and increases almost linearly with the temperature rise is input to the operational amplifier 1. Therefore, this voltage is greatly amplified. The output voltage range can be widened as shown in FIG. Therefore, the effective resolution can be increased, and the accuracy of temperature measurement can be improved accordingly.

In the above embodiment, the wiring resistance r is ignored and the value of the canceling resistance R4 is obtained. However, even if the wiring resistance r cannot be ignored and the wiring resistances vary, The error due to this wiring resistance is measured by the resistance thermometer R
By setting the resistance value obtained by adding or subtracting the resistance value at 0 ° C. to the value of the canceling resistance R4, the resistance temperature detector R including the cancellation of the error of the wiring resistance is Since the offset value which is present at 0 ° C. can be pseudo canceled by the canceling resistor R4 at the time of RV conversion, deterioration of the temperature measurement accuracy due to the error of the wiring resistance can be prevented, and the temperature measurement accuracy can be prevented. Can be improved.

Embodiment 2 FIG. 3 is a block diagram showing a temperature measuring circuit according to a second embodiment of the present invention. In the figure, R is for example a three-wire resistance temperature detector, and R4 is for canceling the offset of the resistance temperature detector R. This is a canceling resistance. However, since the same parts as those in the conventional example are denoted by the same reference numerals, the description of the same parts will be omitted.

Next, the operation will be described. When the three-wire resistance temperature detector R is used, one line thereof is connected to the + side input line of the operational amplifier 1, and the other one line is connected to the-side input line of the operational amplifier 1. Furthermore, the remaining one line is connected to the ground potential of the circuit. The resistance value of the resistance temperature detector R connected in this way changes according to the ambient temperature, but since the resistance temperature sensor R is applied with a constant voltage of Vref from the second constant voltage source 3b. , The change in the resistance is converted into a change in the current flowing through the resistance temperature detector,
This change in current is further converted into a change in voltage by the resistance temperature detector R, the cancel resistor R4, etc., and input to the operational amplifier 1. The operational amplifier 1 amplifies the input voltage and outputs it.

Here, the resistance temperature detector R of this example also has an offset of 100Ω at 0 ° C. Further, assuming that the gain of the operational amplifier 1 in this example is G and the current supplied from the operational amplifier 1 is smaller than the current supplied from the constant voltage source 3, this is ignored, and R >> r, R4> Therefore, assuming that the resistance value of the wiring resistance r is 0, the output voltage V0 of the operational amplifier 1 is V0 = {Vref × R1 × (RR
4)} / {(R + R1) × (R + R2)} × G.
Therefore, if the output voltage V0 at 0 ° C. is 0, it means that the offset component of the resistance temperature detector R at 0 ° C. is canceled in a pseudo manner. For this, 0 ℃
At the time of, {Vref × R1 × (R−R4)} / {(R +
It is sufficient to set R4 = R so that R1) × (R + R2)} = 0. Therefore, the resistance value of the cancel resistor R4 may be set to the resistance value of the resistance temperature detector R at 0 ° C. In the second embodiment, the input temperature range of the resistance temperature detector is 0 ° C to 100 ° C.

FIG. 4 shows an example of resistance characteristics with respect to temperature of the resistance temperature detector R according to the second embodiment, an example of voltage characteristics with respect to temperature when the resistance value change of the resistance temperature detector R is converted into a voltage, and the operational amplifier 1. FIG. 5 is a diagram showing an example of output voltage characteristics with respect to temperature. As shown in FIG. 4A, the resistance temperature detector R of this example is also 0 ° C.
At that time, there is an offset of 100Ω, and the resistance value increases almost linearly as the temperature rises. FIG. 4B shows the characteristic obtained by RV converting the change in the resistance value of the resistance temperature detector R.
Since the canceling resistor R4 is selected to be 100Ω as described above, the voltage becomes 0 mV at 0 ° C., and the voltage increases non-linearly as the temperature rises, and the offset voltage is canceled in a pseudo manner. I know that Therefore, the amplifier output voltage of the operational amplifier 1 also has no offset voltage and is 0 V at 0 ° C., and the output voltage increases non-linearly as the temperature rises.

According to this embodiment, the resistance temperature detector R is zero.
The offset resistance at the time of ℃
Since it is possible to artificially cancel at the time of R-V conversion by means of 4, there is the same effect as in the previous embodiment.

Also in this example, the resistance value obtained by adding and subtracting the error due to the wiring resistance r to the resistance value of the resistance temperature detector R at 0 ° C. is set to the value of the canceling resistance R4. By doing so, the offset amount which the resistance temperature detector R has when the temperature measuring resistor R is 0 ° C., including the cancellation of the error of the wiring resistance, can be canceled in a pseudo manner during the R-V conversion by the canceling resistor R4. The temperature measurement accuracy can be improved.

[0029]

As described above, according to the first aspect of the invention, the resistance temperature detector is provided by providing the canceling resistor that causes the voltage drop in the opposite direction to the voltage drop generated in the resistance temperature detector. The offset that is generated can be canceled in a pseudo manner during resistance-voltage conversion, and the effective resolution of the output voltage can be increased by increasing the amplification factor of the amplifier in the next stage.

According to the second aspect of the present invention, by providing a canceling resistor that causes a voltage drop in the opposite direction to the voltage drop that occurs in the resistance temperature detector, the offset component that the resistance temperature detector has becomes a resistance. -There is an effect that it can be canceled in a pseudo manner at the time of voltage conversion, the amplification factor of the amplifier at the next stage can be increased, and the effective resolution of the output voltage can be increased.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a temperature measuring circuit according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of each part of the temperature measurement circuit shown in FIG.

FIG. 3 is a configuration diagram showing a temperature measuring circuit according to a second embodiment of the present invention.

4 is a characteristic diagram of each part of the temperature measuring circuit shown in FIG.

FIG. 5 is a circuit diagram showing an example of a conventional temperature measuring circuit.

6 is a characteristic diagram of each part of the temperature measurement circuit shown in FIG.

FIG. 7 is a characteristic diagram of each part of a conventional temperature measuring circuit using a thermocouple as a temperature sensor.

FIG. 8 is a table comparing performance differences between a conventional temperature measuring circuit using a thermocouple as a temperature sensor and a temperature measuring circuit using a resistance temperature detector.

FIG. 9 is a circuit diagram showing another example of a conventional temperature measuring circuit.

10 is a characteristic diagram of each part of the temperature measurement circuit shown in FIG.

[Explanation of symbols]

 1 Operational amplifier (amplifier) 2 Constant current source 3 Constant voltage source R Resistance temperature detector R4 Canceling resistance

Claims (2)

[Claims] 1. A resistance temperature detector whose resistance value changes according to temperature, first and second constant current sources for supplying a current to the resistance temperature detector, and a voltage drop generated in the resistance temperature detector which is reverse to A canceling resistor to which a current is supplied from the second constant current source so that a voltage drop in the opposite direction is generated, and the addition component of the voltage drop of the resistance temperature detector and the voltage drop of the canceling resistor is input voltage. And a temperature measuring circuit having an amplifier. 2. A resistance temperature detector whose resistance value changes according to temperature, first and second constant voltage sources for applying a voltage to the resistance temperature detector, and a direction opposite to a current flowing through the resistance temperature detector. The input component is the addition component of the canceling resistance supplied with the voltage from the second constant voltage source so that the current flows, and the voltage drop of the resistance temperature detector and the voltage drop of the canceling resistance. A temperature measuring circuit with an amplifier.