Research On Acquisition And Calibration Method Of Thermocouple Temperature Signal

In the missile ejection test, the acquisition and monitoring of the environment temperature that the key instrument and equipment work on missile have important guiding significance for the evaluation of the equipment’s working condition and model improvement. The extreme environment on missile which includes the violent change of temperature and the complicated strong electromagnetic interference puts forward strict requirement for the stability and reliability of the equipment. To meet the demand of the thermometry on missile, this paper designs a temperature acquisition equipment using thermocouple as the temperature sensitive element under the design of existing acquisition and storage system and the theoretical basis. It is used to measure the environmental temperature parameter on missile and realize the change of temperature to electromotive force. It acquires and codes the output electromotive force of the thermocouple, and uploads the sampling data.Based on the analysis of the design requirement, this paper determines the data acquisition mode and puts forward the overall design scheme. According to the characteristics of the thermocouple temperature measurement, the reference junction compensation scheme is designed which includes the application of the compensation wire and the design of the compensation circuit. The analog signal is adjusted of the gain and filtered to adapt to the input voltage range of the analog to digital converter(ADC) and the accuracy requirement. The sampling and quantization circuit adopts the analog switch to switch the sampling channel. The analog to digital converter converts the analog signal to digital signal. With the design of internal bus and the sampling channel control based on querying the ROM table, the equipment is easy to expand. The FPGA controls multi block acquisition board to work time sharing through the internal bus, and receives data from bus and caches it. The calibration method of the designed thermocouple temperature acquisition equipment is studied. The calibration scheme of the temperature acquisition equipment is designed in combination with the nonlinear compensation measures. Through the analysis of calibration error, a method is put forward to reduce the maximum measurement error of this equipment by adding a correction coefficient.The performance of the thermocouple temperature acquisition equipment is tested comprehensively by constructing the test platform. The reliability and measurement error are analyzed which verifies the equipment that is in full compliance with the design index.