JPS5848597Y2 - Reference junction compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a reference junction compensation circuit for a thermocouple temperature measuring device.

FIG. 1 shows a conventional reference junction compensation circuit of this type.

In the figure, a thermocouple 1 is attached to a terminal board 2, and one end of the thermocouple 1 is connected to a common.

The thermoelectromotive force generated in the thermocouple 1 is amplified by a first amplifier 3 and then led to an input terminal of a third amplifier 5 having a feedback resistor 11 via a resistor 4.

On the other hand, in order to measure the temperature of the terminal board 2, that is, the reference junction temperature, a diode-connected transistor 6 is embedded in the terminal board 2, which has an isothermal effect, so as to be thermally coupled.

This transistor 6 is inserted into the feedback path of the second amplifier 7.

A reference voltage E is connected to the input terminal of the amplifier 7 via an adjustment resistor 8.
ref is supplied and a feedback current substantially equal to the input current flows through transistor 6.

In this case, the base-emitter voltage of the transistor 6, that is, the output voltage of the amplifier 7, has a value corresponding to the reference junction temperature.

This voltage is led via a resistor 9 to the input of the third amplifier 5.

Further, a reference voltage Eref is supplied to the input terminal of the amplifier 5 via an adjustment resistor 10.

In such a configuration, by appropriately selecting the values of the adjustment resistors 8 and 10 and the resistors 4 and 9.11, a thermoelectromotive force according to the reference junction temperature is added to the thermocouple output, so that the so-called reference junction An output related to the compensated thermoelectromotive force is obtained.

However, it had drawbacks such as requiring a large number of amplifiers, making it unsuitable for miniaturization and weight reduction, and being expensive.

An object of the present invention is to eliminate such drawbacks, reduce the number of amplifiers, and realize a small and inexpensive reference junction compensation circuit.

The present invention will be explained in detail below using the drawings.

FIG. 2 shows the configuration of an embodiment of the reference junction compensation circuit according to the present invention.

In FIG. 2, elements equivalent to those in FIG. 1 are given the same reference numerals and their explanations will be omitted.

21 is a zero point adjustment means, 22 is a reference junction temperature detection means, 2
4.25 are first and second resistors, and 26 is an operational amplifier.

The zero point adjustment means 21 is for adjusting the zero point of the operational amplifier 26.

As the adjustment means 21, a potentiometer or the like which divides the reference voltage Eref and outputs the divided voltage may be used, and the output thereof is applied to the non-inverting input terminal of the operational amplifier 26 via the thermocouple 1.

The reference junction temperature detection means 22 is composed of a series circuit of a diode-connected transistor 6 and a resistor 23, and a reference voltage Eref is applied to the transistor 6 via the resistor 23.

The base-emitter voltage of transistor 6 ■BE is the first
is led to the inverting input terminal of an operational amplifier 26 via a resistor 24 .

The inverting input terminal of operational amplifier 26 with feedback resistor 11 is also connected via a second resistor 25 to common.

In such a configuration, the zero point adjustment means 21 collectively adjusts the offset voltage of the operational amplifier 26 and the offset of the reference junction compensation voltage due to variations in the transistor 6 and the resistor 23.

Here, the output impedance of the transistor 6 is the first
The values of the second resistor 25 and the feedback resistor 11 are R2 and R3, respectively, the output of the potentiometer 21 is Vp, and the thermoelectromotive force of the thermocouple 1 is set to be sufficiently small compared to the resistance value R1 of the resistor 24. If Eemf, operational amplifier 2
The output Vo of 6 becomes Vo = (Eemf+vp) -R3-.

Further, in equation (1), if it is assumed that the output Vo does not change with respect to a slight temperature change in the temperature T of the terminal board 2, then the following holds true.

Therefore, by appropriately selecting R1, R2, and R3 so that 0 in equation (1) corresponds to the thermoelectromotive force of thermocouple 1 with reference to 0°C, and equation (2) holds, A signal with reference junction compensation performed at and around the reference junction temperature T can be obtained.

If even more precise compensation is required, it can be further improved by adjusting the resistor 23.

Although the transistor 6 is shown in the embodiment as a device for detecting the reference junction temperature, it is also possible to use a temperature-measuring resistor so as to obtain a desired temperature coefficient.

As explained above, according to the reference junction compensation circuit of the present invention, reference junction compensation can be performed with substantially high accuracy using one amplifier, without requiring many amplifiers unlike conventional circuits. This has the effect that the entire circuit can be made small and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional reference junction compensation circuit, and FIG. 2 is a block diagram showing an embodiment of the reference junction compensation circuit according to the present invention. 1...Thermocouple, 21...Zero point adjustment means, 22...Reference junction temperature detection means, 6...
...Transistor, 24...First resistor, 2
5... Second resistor, 11... Feedback resistor, 26... Operational amplifier.

Claims (1)

[Scope of utility model registration request] A reference junction compensation circuit that detects a reference junction temperature and compensates for the thermoelectromotive force of a thermocouple, comprising a zero point adjustment means and a reference junction temperature detection means for obtaining a signal related to the thermoelectromotive force of the thermoelectric lamp according to the reference junction temperature. and a non-inverting input terminal is connected to the output end of the zero point adjusting means via the thermoelectric lamp, an inverting input terminal is connected to the output end of the reference junction temperature detecting means via a first resistor, and A reference junction compensation circuit comprising an operational amplifier connected to a common via a second resistor and connected to an output terminal via a feedback resistor.