The Research Of Thermocouple’s High Precision Detection Circuit And Signal Processing Method

Temperature is one of the most common and important parameters in industrial and agricultural production, scientific research. The detection method has been perfectly developed. But with the rapid development and in-depth study of polymer materials, composite materials and biotechnology, involving thermal analysis and calorimetry instruments, thermal property testing instruments and other equipment related metrology have increasingly higher requirements for temperature detection range and accuracy. Researching the key technologies about temperature of wide range, high precision and fast detection oriented scientific instruments provides important technical support for the development of scientific research and industrial and agricultural production in the country.Thermocouple with low cost is widely used in wide range of industrial temperature measurement. The dissertation selects N-type thermocouple as temperature sensor, and designs the overall testing program. The specific contents are as follows:Aiming at the thermocouple characteristic of faint output, the 16-fold amplified signal conditioning circuit of a low-pass filter and high-precision signal acquisition circuit based on 24-bit Δ-Σ ADC are designed; For the problem of poor repeatability and consistency of the constant current source, the dissertation designs three-wire platinum resistance detection circuit based on ratio method and constant current source converter to achieve accurate thermocouple cold junction compensation; And it quantitatively analyzes the effects of drift on the system signal sampling and improved circuit design to reduce the impact of drift.In data processing it effectively filters out the noise of the system combined with the use of the moving average filter to extremes filtering method; And it designs algorithm of thermocouple emf converting to temperature combined dichotomy and curve fitting to realize the requirements of temperature measurement accuracy and speed.For the problem of industrial thermocouple with poor accuracy and consistency, The dissertation designs automatic calibration system to improve the efficiency of the calibration. The electrical parameters and temperature is tested by temperature measurement system, and the dissertation t analyzes the error of the results.Experimental results show that it realizes ±0.7℃ accuracy, 0.07℃ precision and temperature resolution of 0.005℃ within the range of 0~700℃ by the N-type thermocouple, and it has good value in terms of temperature-related test equipment.