JPH0217069B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermocouple reference point compensation circuit suitable for use in a temperature measuring device that measures the temperature of a point to be measured using a thermocouple, and more particularly, to The temperature is detected by a temperature detection element such as a transistor, and based on the output of the temperature detection element, a correction voltage having almost the same characteristics as the output change characteristics of the thermocouple with respect to temperature changes at the reference point is generated. The present invention relates to a thermocouple reference point compensation circuit that performs thermocouple reference point compensation.

In recent years, operational amplifiers (hereinafter referred to as OP amplifiers) have made remarkable progress, and along with this, the temperature characteristics of various measurement devices that use these OP amplifiers have improved considerably. However, in thermometers that use thermocouples to measure the temperature at a point to be measured, the accuracy of the circuit (reference point compensation circuit) that compensates the output of the thermocouple according to the reference point temperature of the thermocouple is limited. This directly affects the measurement accuracy, and the accuracy of the thermometer cannot be increased beyond the accuracy of this reference point compensation circuit. Therefore, in this type of reference point compensation circuit, the reference point temperature of the thermocouple is usually measured using a transistor with small variation in characteristics, and this measurement result is added to the thermocouple output to compensate for the increase in the reference point temperature. However, as is well known, transistors have linear temperature characteristics, so simply adding the output of this transistor to the output of the thermocouple will result in a non-linear It is not possible to completely compensate for the output of a thermocouple.

In view of the above circumstances, the present invention provides a method for compensating for a difference between a change in the output of a thermocouple due to a temperature change at a reference point and a change in output of a transistor due to a change in temperature at the reference point, which is caused by a change in temperature at the reference point of the thermocouple. The object of the present invention is to provide a thermocouple reference point compensation circuit that can reduce measurement errors to almost zero.

In order to achieve this object, the thermocouple reference point compensation circuit according to the present invention includes a transistor that detects the reference point temperature accompanying a temperature change of the thermocouple that detects the temperature of the object to be measured. a reference point temperature detection circuit that outputs a predetermined voltage according to the temperature change based on the detection result of the transistor;
The output voltage of the reference point temperature detection circuit is compared with a preset set voltage, and based on the comparison result, a predetermined polygonal line having characteristics corresponding to a temperature change of the thermocouple with respect to a change in the reference point temperature is determined. a polygonal function generation circuit that generates a correction voltage based on a function; and a voltage shift circuit that compensates by shifting the output of the thermocouple by a voltage resulting from the addition of the output voltage of the reference point temperature detection circuit and the correction voltage of the polygonal function generation circuit. It is characterized by having the following.

The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 is a circuit diagram showing an example of a temperature measuring circuit to which a first embodiment of the thermocouple reference point compensation circuit according to the present invention is applied.

In this figure, reference numeral 1 is a thermocouple that detects the temperature of the object to be measured, and one end of this thermocouple 1 is the first
The other end is connected to the third input terminal 4c of the voltage shift circuit 4 through the second junction (reference point) 2b and the terminal 3 in series. has been done. Voltage shift circuit 4
is an OP amplifier 5 whose non-inverting input terminal is connected to the third input terminal 4c, first and second input resistors 6 and 7 whose one end is connected to the inverting input terminal of this OP amplifier 5, and grounding. It has a resistor 8 and a feedback resistor 9, and the other ends of the first and second resistors 6 and 7 are connected to the first and second input terminals 4a and 4b of the voltage shift circuit 4, respectively. , the other end of the ground resistor 8 is grounded, and the other end of the feedback resistor 9 is connected to the output terminal of the OP amplifier 5. Therefore, when the thermocouple 1 detects the temperature of the object to be measured and outputs a thermoelectromotive voltage corresponding to the detection result, the voltage shift circuit 4 causes the first,
The thermoelectromotive voltage is voltage-shifted by each voltage supplied to the second input terminals 4a and 4b and output from the output terminal 4d.

Reference numeral 10 is a reference point temperature detection circuit for detecting the temperature of the first and second junction points 2a and 2b, which are the reference points of the thermocouple 1; A transistor (temperature detection element) 11 that is thermally short-circuited with
an OP amplifier 12 whose inverting input terminal is connected to the emitter of the transistor 11, and whose output terminal is connected to the connection point _P1 between the base and collector of the transistor 11; A resistor 14 inserted between the power supply terminal 13
and a resistor 15, a variable resistor 16, and a resistor 17 which are successively inserted in series between the power supply terminal 13 and the ground point, and the voltage obtained at the sliding terminal of the variable resistor 16 for zero adjustment. The configuration is such that the voltage at the non-inverting input terminal of the OP amplifier 12 can be varied.
Therefore, the first and second junction points 2a, 2b
If the temperature changes, the transistor 11 detects this and changes the output voltage of the OP amplifier 12,
The voltage obtained as a result is applied to the reference point temperature detection circuit 10.
Temperature detection is output from the output terminal 18 of the voltage shift circuit 4 and supplied to the first input terminal 4a of the voltage shift circuit 4, thereby correcting the output of the thermocouple 1, and output from the output terminal 4d of the voltage shift circuit 4. The signal is made to have an output voltage characteristic as shown in Figure 2A.

In this way, if the reference point temperature of the thermocouple 1 rises and the output voltage of this thermocouple 1 decreases, the transistor 11 of the reference point temperature detection circuit 10 will respond accordingly.
The voltage between the base and emitter of the thermocouple 1 decreases, and the output voltage of the reference point temperature detection circuit 10 decreases, and this decrease is reversed by the voltage shift circuit 4 and
is added to the output of

Further, the output of the reference point temperature detection circuit 10 is also supplied to the input terminal 20 of the polygonal line function generation circuit 19. The polygonal function generating circuit 19 includes a resistor 22 that divides the voltage +V applied to its positive power supply terminal 21;
23, and a resistor 2 inserted in series between the connection point P ₂ of these resistors 22 and 23 and the input terminal 20.
4, 25 and the connection point P ₃ of these resistors 24, 25
OP amplifier 2 whose non-inverting input terminal is connected to
6, a resistor 27 inserted between the inverting input terminal of the OP amplifier 26 and the ground point, and the anode and cathode thereof are connected in series in sequence between the inverting input terminal and the output terminal of the OP amplifier 26. It generates a voltage (correction voltage) having a linear function characteristic corresponding to the output of the reference point temperature detection circuit 10 and outputs it from its output terminal 29, and outputs it from the output terminal 29. It is supplied to the second input terminal 4b. That is, when the voltage supplied to the input terminal of the polygonal function generating circuit 19 decreases and the non-inverting input terminal voltage of the OP amplifier 26 becomes smaller than the inverting input terminal voltage (approximately OV), the OP amplifier 26 Switching the output to the negative side makes the diode 28 conductive, making the anode voltage of the diode 28 equal to the non-inverting input terminal voltage of the OP amplifier 26, and outputting this voltage from the output terminal 29 to the voltage shift circuit 4. supply Therefore, for example, transistor 11
When the temperature reaches 25°C, the line function generating circuit 19 operates and outputs a correction voltage from its output terminal 29, and when the temperature reaches 0°C, the reference point temperature detection circuit 10 operates.
The amount of correction due to the output of the thermocouple 1 matches the output error of the thermocouple 1, and furthermore, the amount of correction due to the output of the reference point temperature detection circuit 10 and the output of the polygonal function generation circuit 19 at 25°C and 50°C matches the output error of the thermocouple 1. Each resistor 6 to 9, 14, 15, 17, 2 to match the output error of 1
If each value of 2 to 24, 27 and the value of the variable resistor 16 are set, the error will be smaller than the output voltage error (a) obtained by using only the reference point temperature detection circuit 10, as shown in FIG. A small output voltage error (b) can be obtained.

FIG. 3 shows the second reference point compensation circuit according to the present invention.
FIG. 2 is a circuit diagram showing an example of a temperature measurement circuit to which an embodiment is applied. The circuit shown in this figure is different from the circuit shown in FIG.
After adding the outputs of
44 and an OP amplifier 45, and added to the output of the thermocouple 1. In this way, the addition circuit 41 is provided between the reference point temperature detection circuit 10, the polygonal function generation circuit 19, and the voltage shift circuit 46, so that the shock when switching the operation of the polygonal function generation circuit 19 is not directly transmitted to the voltage shift circuit 46. You may choose not to have one.

Further, in each of the embodiments described above, the operation switching point of the polygonal function generating circuit 19 is set to one, but if two or more operation switching points are provided, even more precise approximation can be performed.

Also, instead of the polygonal function generating circuit 19, D/
A function generator using an A converter or other components is provided, and the output of the reference point temperature detection circuit 10 is compared or A/D.
It is also possible to convert it, determine its size, and control the function generator based on the result of this determination to generate a function voltage that approximates the temperature characteristics of the thermocouple 1.

As described above, the thermocouple reference point compensation circuit according to the present invention detects the reference point temperature of the thermocouple using a transistor, and based on the detection result, the temperature characteristics with respect to changes in the thermocouple reference point temperature are determined. Since the output of the thermocouple is compensated for by generating a correction voltage with characteristics close to , the difference between the change in the output of the thermocouple with respect to the temperature change at the reference point and the change in the output of the transistor with respect to the temperature change at the reference point can be reduced. This eliminates measurement errors due to temperature changes at the reference point of the thermocouple.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a temperature measurement circuit to which the first embodiment of the thermocouple reference point compensation circuit according to the present invention is applied, FIG. 2 is a characteristic diagram for explaining the same embodiment, and FIG. FIG. 2 is a circuit diagram showing an example of a temperature measuring circuit to which a second embodiment of the thermocouple reference point compensation circuit according to the present invention is applied. 1...Thermocouple, 4...Voltage shift circuit, 10...
...Reference point temperature detection circuit, 11...Transistor,
19... Linear function generation circuit.

Claims (1)

[Claims] 1 Reference point temperature detection that has a transistor that detects a reference point temperature accompanying a temperature change of a thermocouple that detects the temperature of the object to be measured, and outputs a predetermined voltage according to the temperature change based on the detection result of the transistor. The circuit compares the output voltage of the reference point temperature detection circuit with a preset set voltage, and based on the comparison result, has a characteristic corresponding to a temperature change of the thermocouple with respect to a change in the reference point temperature. A polygonal function generation circuit that generates a correction voltage according to a predetermined polygonal function, and the output of the thermocouple is compensated by shifting the output voltage of the reference point temperature detection circuit by a voltage obtained by adding the correction voltage of the polygonal function generation circuit. A reference point compensation circuit for a thermocouple, comprising a voltage shift circuit.