A high-precision thermocouple input module and measurement method

Abstract

The invention relates to a high-precision thermocouple input module, which includes an isolator, an amplifier, an analog-to-digital conversion unit, a controller, a digital-to-analog conversion unit, and an electronic switch. , the output end of the analog-to-digital conversion unit is connected to the controller, which is characterized in that: the grounding end of the isolator leads out to the grounding interface while being grounded, and the voltage output end of the isolator leads out to two interfaces at the same time. The signal obtained by the digital-to-analog conversion unit outputs a feedback signal to the digital-to-analog conversion unit, and the output terminal of the digital-to-analog conversion unit leads out to an output interface. Another technical solution of the present invention is to provide a high-precision thermocouple input measurement method, using the above-mentioned thermocouple input module. The invention has the advantages of ensuring that the overall absolute accuracy of the thermocouple signal is 0.1-0.2°C, and the relative accuracy can reach 0.005-0.01%, which can meet the real needs of the industrial control process.

Description

technical field [0001] The invention relates to a high-precision thermocouple input module and a measurement method, which are used for improving the measurement accuracy of small signals such as thermocouples or millivolts, and belong to the technical field of automatic control instruments. Background technique [0002] The thermocouple is composed of two metal wires with different components connected at their ends to form a closed loop. One end that is directly used to measure the temperature of the medium is called the working end (also known as the measuring end), and the other end is called the cold end (also known as the compensation end). end), when there is a temperature difference between the working end and the cold end, a current will flow through the loop, and there will be a thermal electromotive force (Seebeck effect) between the two ends. A voltage output that is approximately proportional to the temperature difference. But this voltage is very small. For ex...

AI Technical Summary

Problems solved by technology

[0005] On the surface, the measurement accuracy of thermocouple signals will be concentrated on the analog-to-digital converter (ADC). Generally, the analog-to-digital converter uses 12 bits, although the theoretical resolution of the analog-to-digital converter is 1 / 4096 (that is, 2 / 10,000). , but due to the reference voltage of components such as amplifiers and analog-to-digital converters and the temperature drift of components such as resistors, etc., in fact, the measurement accuracy of the entire thermocouple signal is generally between 0.1 and 0.2%. The digital converter is increased to 13 or 14, or even 15, but the overall measurement accuracy cannot be improved much

[0006] In industrial process control, this relative accuracy is not a big problem for process variables such as valve opening, pressure, flow, liquid level, voltage and current of the actuator, but for temperature signals, because it has no specific range, Under normal circumstances, the thermocouple input module is compatible with thermocouple signals of various graduation numbers, and the thermoelectric potential signal used will have enough upper limit margin, and the upper limit of the converted temperature range will reach 2000°C. At this time, the relative accuracy is converted into an absolute value. It will reach 2℃~4℃

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