Hardware Design Of High Precision Thermocouple Acquisition System

A thermocouple sensor is a kind of temperature measurement sensor based on the thermoelectric effect.The measurement principle is to synthesize the thermoelectric effect potential difference and cold junction compensated to obtain the measured temperature value.The sensor is commonly used in engine detection,metallurgy,biology,agriculture,and other industries.In these applications,there are usually multiple temperature measuring points,wide temperature ranges,and a variety of thermocouple types.Based on these scenarios,the thermocouple acquisition system is born on demand,which greatly improves the convenience of user measurement.With the development of technology and the changes in the international situation,the research of domestic thermocouple acquisition systems has put forward the requirements of multi-channel,high precision,high resolution,rapid measurement,and support for various thermocouple types.Therefore,with high precision and multi-channel as the core,the thesis studies the hardware design and implementation of high precision thermocouple acquisition system,and proposes a hardware system to achieve high precision thermocouple acquisition,which has 48 channels,a temperature range covering-200～1820℃,temperature accuracy up to ±0.25℃.The main research and innovation contents are as follows:1.The design of high-precision signal conditioning and acquisition.Firstly,according to the precision requirements of different voltage gears and temperature measurements,the programmable gain circuit is designed by the combination of a relay and an analog switch.Low pass filter and programmable filter are designed to improve the signal-to-noise ratio.Design multiplexing circuit and acquisition circuit group form.2.The design and optimization of cold junction compensation.The error of thermocouple acquisition includes the error of cold junction temperature in addition to the error of potential difference measurement.The cold junction compensation structure of the usual thermocouple acquisition instrument is simple.It is only connected through the contact mode between the temperature sensor and the cold junction electrode of the thermocouple socket.This method has the problem that the cold junction temperature response time is long,and it is easy to be affected by external interference.Therefore,the thesis designed a special cold junction compensation structure,and independently designed a thermocouple socket,and isothermal block,improving the heat conduction rate and heat capacity,reducing the sensitivity to external interference,and improving the cold junction temperature response speed.3.The design of multi-channel switching control.In the multichannel time-sharing multiplexing circuit,the number of analog switching channels is not sufficient,so the multi-chip splicing method is adopted.However,this method will cause signal interference when switching between two analog switches.In order to solve this problem,a control method of switching between chips is proposed.Finally,the test platform was built,and through the test verification of the system,the accuracy and range of temperature and voltage measurement,as well as various functions,met the expected goals.