JP3222367B2 - Temperature measurement circuit - Google Patents

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 a temperature by using a temperature measuring resistor or a thermistor (hereinafter referred to as a temperature measuring low antibody) as a temperature sensor.

[0002]

BACKGROUND ART FIG. 5 is a circuit diagram showing an example of a conventional temperature measuring circuit, reference numeral 1 denotes an operational amplifier of the single power supply which amplifies a voltage corresponding to the resistance change of the resistance temperature detector R, 2
Is a constant current source for supplying a current I to the resistance thermometer R, etc., R2,
R3 is a resistor that determines a circuit constant for setting the amplification factor and the like of the operational amplifier 1, and r is a wiring resistance.

Next, the operation will be described. RTD R
Changes its resistance value depending on the ambient temperature. Therefore,
When the resistance value changes, the voltage drop due to the resistance temperature detector R also changes. Therefore, by supplying a constant current I from the constant current source 2 to the resistance temperature detector R, the change in the resistance causes the voltage change. (RV conversion), and this is input to the arithmetic circuit 1 of a single power supply. The arithmetic circuit 1 of a single power supply amplifies and outputs the voltage drop due to the resistance bulb R. For this reason, the output voltage of the operation circuit 1 of a single power supply has a value corresponding to the temperature around the temperature measuring resistor R.

Here, when the resistance value of the resistance thermometer R changes linearly with respect to temperature as shown in FIG. 6A, the above-mentioned RV conversion causes the resistance to change as shown in FIG. The change in the voltage becomes almost linear with respect to the change in the resistance value, and the change in the voltage is amplified by the operational amplifier 1 having a single power supply.
As shown in (C), the voltage is output as a linear voltage change with respect to the temperature.

Since the current coming from the operational amplifier 1 is smaller than the current I supplied from the constant current source 2, this is ignored, and since R >> r, the wiring resistance r is assumed to be 0. Assuming that the gain of the operational amplifier 1 is G, the operational amplifier 1
Is the output voltage V0 = R × I × G. Further, FIG.
In the characteristic diagrams shown in (B) and (C), the shaded portions indicate the inoperable range of the single-power-supply operational amplifier 1, but the voltage after the RV conversion and the dual-power-supply operational amplifier None of the output voltages of
It can be seen that the single-power-supply operational amplifier 1 operates with sufficient performance.

When the temperature measuring resistor R is used as a temperature sensor as described above, the change in voltage due to the change in resistance is a very small signal. Must be an amplifier. But,
Since a high-precision single-power operational amplifier 1 is generally expensive, it is generally desirable to use an inexpensive high-precision dual-power operational amplifier.

Therefore, when the operational amplifier 1 of a single power supply used in the conventional circuit of FIG. 5 is replaced with an operational amplifier of a dual power supply, the resistance value of the resistance bulb R has a resistance value as shown in FIG. Varies with temperature. This change in resistance value is the same as R
The voltage change with respect to the temperature as shown in FIG. 7B by the -V conversion is input to the operational amplifiers of both power supplies. The change in the voltage is amplified by the operational amplifier of the dual power supply, and is output as a voltage corresponding to the temperature as shown in FIG.

Here, when Pt100 is used as the resistance temperature detector R, when the input temperature range is -200 ° C. to 100 ° C., the output value of the resistance temperature detector R is 18.5Ω to 139.64.
Ω, the output voltage of the operational amplifier is 1.32 V to 1
It becomes 0V. However, the amplification factor at this time is 71.6 times (the amplification factor is such that the maximum input is 10 V), and the current supplied to the resistance bulb R is 1 mA. Therefore, the specifications of the operational amplifier must satisfy the above numerical values, but the specifications of the high-precision dual power supply operational amplifier and the high-precision single power supply operational amplifier are as shown in the table of FIG. It is.

As shown in the table of FIG. 8, when the power supply voltage of the operational amplifier is 0 and 15 V, and the resistance bulb R is -2.
In the case of 18.5Ω at 00 ° C., the output of the operational amplifier is 1.32 V. However, this is too low for the input voltage, and the specifications of the high-precision dual-power operational amplifier shown in FIG. / Output specification), so that an operational amplifier with dual power supplies cannot be used in the conventional circuit shown in FIG.

The reason why the operational amplifier of the dual power supply cannot be used is also shown in the characteristic diagram of FIG. 7B, and the range indicated by the diagonal lines in the characteristic diagram indicates that the operational amplifier of the dual power supply cannot operate. The results of converting the resistance change of the resistance temperature detector R into the voltage change within the range are all in the shaded range. Therefore, as shown in FIG. 7 (C), a part of the output voltage of the operational amplifier of the dual power supply also falls within the inoperable range, and the operational amplifier of the dual power supply which is inexpensive with the conventional configuration is used. It is clear that cannot be used.

FIG. 9 is a circuit diagram showing another example of the conventional temperature measuring circuit. In FIG. 9, a constant voltage source 3 is connected to an input of an operational amplifier 1 having a single power supply. FIG. 5 shows another configuration.
And the same components are denoted by the same reference numerals, and a description thereof will be omitted.

Next, the operation will be described. RTD R
Changes its resistance value depending on the ambient temperature, for example, as shown in FIG. In this case, since the constant voltage source 3 of the constant voltage Vref is connected to the input measurement of the operational amplifier 1 of the single power supply, the current flowing through the resistance bulb 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. Assuming that the gain of the single power supply operational amplifier 1 is G, the output voltage V0 of this operational amplifier 1 is V0 = R × {Vref (R + R1)} ×
G, and a non-linear output voltage is obtained with respect to the temperature as shown in FIG.

However, since the current coming from the operational amplifier 1 is smaller than the current I supplied from the constant voltage source 3, this is ignored, and since R >> r, the wiring resistance r is assumed to be 0. I ignored it. In this case, as shown in FIGS. 10B and 10C, the voltage change corresponding to the temperature change becomes non-linear, but both the voltage after the RV conversion and the amplifier output voltage are equal to those of the single-power supply operational amplifier 1. It can be seen that it is within the operable range and operates without any problem.

In this example, too, it is desired to use an inexpensive dual power supply operational amplifier instead of the expensive and highly accurate single power supply operational amplifier 1 used in the conventional circuit of FIG. But,
When an operational amplifier with dual power supplies is used in the circuit of FIG. 9, the resistance change of the resistance bulb R is the same as that described above as shown in FIG. The converted voltage change is as shown in FIG. 11B, which falls within the inoperable range (the shaded range in the figure) of the operational amplifier of the dual power supply. For this reason, the output voltage of the operational amplifier of the dual power supply is also shown in FIG.
As can be seen from FIG. 1 (C), most of the operational amplifier enters the inoperable range of the operational amplifier (the shaded area in the figure), so that an inexpensive dual-power-supply operational amplifier cannot be used.

[0015]

Since the conventional temperature measuring circuit using a resistance temperature detector as a temperature sensor is constructed as described above, it amplifies a minute voltage accompanying a resistance change of the resistance temperature detector R. And the resistance thermometer R is-
Since there is only a dozen Ω at 200 ° C., the minute voltage is low, and it is necessary to amplify the minute voltage using a high-precision single-supply operational amplifier 1. If the input voltage is too low, it will not operate normally. It has not been possible to use an accurate and inexpensive dual power operational amplifier. Therefore, there is a problem that the temperature measurement circuit becomes expensive.

Accordingly, the present invention has been made to solve the above-mentioned problems, and amplifies a minute voltage accompanying a resistance change of a resistance temperature detector using an inexpensive and highly accurate operational amplifier of a dual power supply. It is an object of the present invention to obtain a temperature measurement circuit that can perform the measurement.

[0017]

According to a first aspect of the present invention, there is provided a temperature measuring circuit for supplying a current to a temperature sensor .
Input the second constant current source and the voltage drop of the temperature sensor
An operational amplifier for both power and voltage, the temperature with the voltage drop of the voltage drop in the same direction caused by the temperature sensor occurs
The terminal voltage of the temperature sensor rises with respect to the ground potential , and
The input voltage to the operational amplifier is
It is obtained by a offset resistance supplied with current from the second constant current source to be within work tolerance.

According to a second aspect of the present invention, there is provided a temperature measuring circuit comprising: a first and a second constant voltage sources for applying a voltage to a temperature sensor; and a dual voltage source having a voltage drop of the temperature sensor as an input voltage.
An operational amplifier source, the terminal voltage of the temperature sensor with the voltage drop of the voltage drop in the same direction caused by the temperature sensor is caused to rise relative to the ground potential, and the operational amplifier
Input voltage within the normal operating range of the operational amplifier
Wherein at the second one with a offset resistance supplied with current from the constant voltage source so.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. 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 type thermistor or a resistance thermometer, and 4 is a high-precision dual power operational amplifier. Then, the input voltage corresponding to the resistance value of the resistance bulb R is amplified and output. R4 is an offset resistor inserted between the input side of the operational amplifier 4 for both power supplies and the ground potential in order to raise the voltage drop of the resistance thermometer R as a whole and offset it. However, the same parts as those of the conventional example are denoted by the same reference numerals, and the description of the same constituent parts will be omitted.

Next, the operation will be described. When used as a three-wire type resistance thermometer R, one line is connected to the + input line of the operational amplifier 4 of the dual power supply, and the other line is connected to the-input line of the operational amplifier 1. The other line is connected to the ground potential via an offset resistor R4. The resistance value of the temperature measuring resistor R connected in this way changes depending on the ambient temperature. However, since the current I is supplied from the constant current source 2 to the temperature measuring resistor R,
The change in the resistance is input to the operational amplifier 4 as a change in the voltage drop due to the resistor. The operational amplifier 4 amplifies and outputs the input voltage.

The resistance thermometer R used in this example is also -200.
Although it has a resistance value of about several tens of ohms at ° C, a total of 2I current flows from the two constant current sources 2 to the offset resistance R4 inserted between the resistance bulb R and the ground. The voltage at the connection point between the resistance bulb R and the offset resistor R4 is 2
I × R4, and the increased voltage is applied to the resistance bulb R
, That is, the value obtained by adding R × I is input to the operational amplifier 4 of the dual power supply. Therefore, when the output voltage V0 of the operational amplifier 4 of both power supplies at this time is obtained,
0 = R × I × G + 2 × R4 × I. Where R
>> r, R4 >> r, so it is assumed that r = 0,
Since the current flowing out of the operational amplifier 4 is smaller than the current I from the constant current source 2, this current is ignored and the operational amplifier 4
Is G.

FIG. 2 shows an example of the resistance characteristic of the resistance thermometer R with respect to the temperature in this example, an example of the voltage characteristic with respect to the temperature when the change in the resistance value of the resistance R is converted into a voltage, and the temperature of the operational amplifier 4. FIG. 6 is a diagram showing an example of output voltage characteristics with respect to FIG. As shown in FIG. 2 (A), the resistance bulb R of this example has a temperature of -200 ° C.
At this time, there is a resistance value of more than ten Ω, and the resistance value increases almost linearly with an increase in temperature. FIG. 2B shows a characteristic obtained by RV conversion of the change in the resistance value of the resistance bulb R. In this case, because of the presence of the offset resistor R4 as described above, there is a voltage of 3.5 V at −200 ° C.
It increases linearly with increasing temperature, and at 100 ° C. 3.6
It turns out that it becomes 4V. Accordingly, a voltage of 3.5 V to 3.64 V is input to the operational amplifier 4 of the dual power supply, and FIG.
As shown in (C), the amplifier output voltage was 3.5 V at -200 ° C., and increased almost linearly with the rise in temperature.
It becomes 12.2V at 00 ° C.

After all, as can be seen from FIGS. 2B and 2C, both the voltage obtained by RV conversion of the change in the resistance value of the resistance temperature detector R and the output voltage of the amplifier are the same. Since the input / output voltage range is within the operable input / output voltage range of the operational amplifier 4 of the power supply, the operational amplifier 4 of the dual power supply operates normally and outputs a voltage corresponding to the ambient temperature of the resistance bulb R. In the above example, the voltage drop due to the offset resistor R4 is about 2
If it is set to about V, that is, if a resistance value that can obtain a voltage drop of about 2 V is set to the value of the offset resistor R4, the temperature above the lowest measured temperature (−200 ° C. in this example) is set to the operational amplifier of the dual power supply. 4 can be measured correctly.

According to the present embodiment, the voltage drop of the offset resistor R4 is added to the terminal voltage of the resistance bulb R, and the voltage drop of the resistance bulb R is raised as a whole to offset the voltage. Is added to the input voltage of the amplifier, so that the operational amplifier 4 of the dual power supply operates normally even if the temperature measuring resistor R having a resistance value of more than ten ohms is used at -200 ° C. Since the input voltage range can be within the range, the operational amplifier 4 of a dual power supply with high accuracy and low cost can be used, and the temperature measuring circuit can be configured at low cost.

Embodiment 2 FIG. 3 is a block diagram showing a temperature measuring circuit according to a second embodiment of the present invention. In the drawing, R corresponds to, for example, a three-wire type thermistor or a temperature measuring resistor, and 4 corresponds to the resistance value of the temperature measuring resistor R. A high-precision dual-power operational amplifier R4 for amplifying and outputting an input voltage to be input, and an input side of the dual-power operational amplifier 4 for increasing and offsetting the voltage drop of the resistance temperature detector R as a whole. And an offset resistor inserted between the power supply and the ground potential. However, the same parts as those of the conventional example are denoted by the same reference numerals, and the description of the same constituent parts will be omitted.

Next, the operation will be described. When used as a three-wire type resistance thermometer R, one line is connected to the + input line of the operational amplifier 4 of the dual power supply, and the other line is connected to the-input line of the operational amplifier 1. The other line is connected to the ground potential via an offset resistor R4. The resistance value of the temperature measuring resistor R connected in this way changes depending on the ambient temperature. However, since a constant voltage of Vref is applied from the constant voltage source 3 to the temperature measuring resistor R, Is converted into a change in the current flowing through the resistance thermometer, and the change in the current is further converted into a voltage change by the resistance R or the offset resistor R4 and input to the operational amplifier 4. The operational amplifier 4 amplifies and outputs the input voltage.

The resistance temperature detector R used in this example is also -200.
Although it has only a resistance value of about several tens of ohms at the time of ° C., the offset resistance R inserted between the resistance bulb R and the ground.
4, a current flows from the two constant voltage sources 3 so that the voltage at the connection point between the temperature measuring resistor R and the offset resistor R4 is R4 ×
Vref × (2 × R1 + R) ｛R1 × R1 + R × (R1
+ R4) + 2 × R1 × R4}, and the increased voltage corresponds to the voltage drop of the resistance bulb R, that is, R × Vref
× R1 ｛R1 × R1 + R × (R1 + R4) + 2 × R1 ×
The value obtained by adding R4 # is input to the operational amplifier 4 of the dual power supply.

Therefore, when the output voltage V0 of the operational amplifier 4 of both power supplies at this time is obtained, V0 = R × Vref × R1
{R1 × R1 + R × (R1 + R4) + 2 × R1 × R4}
× G + R4 × Vref × (2 × R1 + R) ｛R1 × R1
+ R × (R1 + R4) + 2 × R1 × R4}. However, since R >> r and R4 >> r, the resistance value of the wiring resistance r is regarded as 0, and the current flowing out of the operational amplifier 4 is smaller than the current I flowing from the constant current source 2. This current is ignored, and the gain of the operational amplifier 4 is set to G.

FIG. 4 shows an example of the resistance characteristic of the resistance thermometer R with respect to the temperature in this example, an example of the voltage characteristic with respect to the temperature when the change of the resistance value of the resistance R is converted into a voltage, and the temperature of the operational amplifier 4. FIG. 6 is a diagram showing an example of output voltage characteristics with respect to FIG. As shown in FIG. 4A, the resistance thermometer R of the present example is also −200 ° C.
At this time, there is a resistance value of more than ten Ω, and the resistance value increases almost linearly with an increase in temperature. FIG. 4B shows a characteristic obtained by RV converting the change in the resistance value of the resistance bulb R. In this case, because of the presence of the offset resistor R4 as described above, there is a voltage of 3.5 V at −200 ° C.
It can be seen that it increases non-linearly with increasing temperature and becomes 3.64 V at 100 ° C. Therefore, a voltage of 3.5 V to 3.64 V is input to the operational amplifier 4 of the dual power supply, and as shown in FIG. 4C, the output voltage of the operational amplifier 4 is 3.5 V at -200 ° C. Increases non-linearly with increasing temperature to 12.2 V at 100 ° C.

After all, as can be seen from FIGS. 4B and 4C, the voltage obtained by RV conversion of the change in the resistance value of the resistance bulb R and the output voltage of the operational amplifier 4 of the dual power supply are obtained. Since both of them are within the input / output voltage range in which the operational amplifier 4 of the dual power supply can operate, the operational amplifier 4 of the dual power supply operates normally, and the voltage corresponding to the ambient temperature of the resistance temperature detector R. Is output. In the above example, if the voltage drop due to the offset resistor R4 is about 2 V, that is, if the value of the offset resistor R4 is set to a resistance value that can obtain a voltage drop of about 2 V, the lowest measurement temperature (in this example, The temperature above −200 ° C.) can be correctly measured using the operational amplifier 4 of the dual power supply.

According to the present embodiment, the voltage drop of the offset resistor R4 is added to the terminal voltage of the resistance thermometer R, and the voltage drop of the resistance thermometer R is raised as a whole. Is added to the input voltage of the amplifier, so that the operational amplifier 4 of the dual power supply operates normally even if the temperature measuring resistor R having a resistance value of more than ten ohms is used at -200 ° C. Since the input voltage range can be set within the range, the operational amplifier 4 of dual power supply with high accuracy and low cost can be used, and the same effect as in the previous embodiment can be obtained.

According to the above embodiments, when the temperature is -200.degree. C., which is the minimum temperature to be measured by the resistance bulb R, the voltage caused by the voltage drop generated by the resistance bulb R is calculated by the two power supplies. The resistance value of the offset resistor R4 is determined so as to be equal to or higher than the lower limit value of the operable input voltage range of the amplifier 4. The output voltage obtained by amplifying the voltage obtained by adding the voltage due to the voltage drop generated at R to the voltage drop generated at the offset resistor R4 by the operational amplifier 4 of the dual power supply is the upper limit of the operable output voltage range of this amplifier. It is also possible to determine the resistance value of the offset resistor R4 and adjust the temperature range to be measured by the resistance bulb R as described below.

[0033]

As described above, according to the first aspect of the present invention, the voltage drop in the same direction as the voltage drop generated by the temperature sensor is provided.
Occurs, and the terminal voltage of the temperature sensor becomes the ground potential.
And the input voltage to the operational amplifier increases.
Constant current so that it is within the normal operating tolerance of the operational amplifier
And an offset resistor to which a current is supplied from a source , so that the voltage due to the voltage drop of the resistance temperature detector is raised as a whole and offset, so that the amplification of this voltage is inexpensive and easy. There is an effect that a highly accurate dual power supply operational amplifier can be used.

According to the second aspect of the present invention, a temperature sensor is provided.
Voltage drop in the same direction as the voltage drop
The terminal voltage of the temperature sensor rises with respect to the ground potential.
First, the input voltage to the operational amplifier is
Supply current from constant voltage source within normal operation allowable range
The Rukoto a offset resistor that is, since the voltage due to a voltage drop of the resistance temperature detector Overall raised are offset, an inexpensive and highly accurate dual supply of the operational amplifier to amplify the voltage Can be used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a temperature measurement circuit according to Embodiment 1 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 measurement circuit according to a second embodiment of the present invention.

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

FIG. 5 is a configuration diagram illustrating an example of a conventional temperature measurement 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 measurement circuit using an operational amplifier of dual power supplies.

FIG. 8 is a table showing specifications of a dual power supply operational amplifier and a single power supply operational amplifier.

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

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

FIG. 11 is a characteristic diagram of each part of a conventional temperature measurement circuit using a dual power supply operational amplifier.

[Explanation of symbols]

 1,4 operational amplifier 2 constant current source 3 constant voltage source R RTD R4 offset resistor

Claims (2)

(57) [Claims] 1. A temperature sensor whose resistance value changes with temperature.
And first and second constant current sources for supplying current to the temperature sensor.
When,Of a dual power supply with the voltage drop of the temperature sensor as an input voltage
An operational amplifier,  The voltage drop in the same direction as the voltage drop generated by the temperature sensor is
And the terminal voltage of the temperature sensor
Then riseAnd the input voltage to the operational amplifier is
Within the normal operation tolerance of the operational amplifierSo the second
Offset resistor supplied with current from a constant current sourceAnti andTo
Equipped temperature measurement circuit. 2. A temperature sensor whose resistance value changes with temperature.
And first and second constant voltage sources for applying a voltage to the temperature sensor.
When,Of a dual power supply with the voltage drop of the temperature sensor as an input voltage
An operational amplifier,  The voltage drop in the same direction as the voltage drop generated by the temperature sensor is
And the terminal voltage of the temperature sensor
Then riseAnd the input voltage to the operational amplifier is
Within the normal operation tolerance of the operational amplifierSo the second
Offset resistor supplied with current from a constant voltage sourceAnti andTo
Equipped temperature measurement circuit.