Research On Automatic Verification System Of Precision Thermocouple

As one of the most widely used contact temperature detection sensors,thermocouples are widely used in many important fields such as aerospace,petrochemical industry,and hydropower generation.The accuracy of the displayed value is directly related to the reliability of the value transmission,and also determines whether the product quality of related production enterprises is qualified.According to the relevant provisions of China’s "Measuring Law",in order to ensure the accuracy of thermocouple temperature measurement and standardize thermocouple temperature measurement standards,it is necessary to perform strict periodicity on newly produced thermocouples and thermocouples in use according to the national verification regulations Accreditation.The verification of thermocouple is very complicated.In order to improve the efficiency and accuracy of thermocouple verification,related enterprises and scientific research institutions began to develop thermocouple verification system.However,most of the verification systems use the mechanical motion scanning switch to switch the thermoelectric potential.Affected by the switch conversion characteristics,it takes about 2 seconds to complete one action switching and read the data.At the same time,when verifying multiple thermocouples,the data acquisition time will be correspondingly increased.Through the actual detection of furnace temperature,it is found that the furnace temperature has been in irregular change after reaching the verification temperature The longer the data reading time is,the greater the furnace temperature change is,and the greater the thermocouple calibration error is.1.In view of the above situation,based on the relevant detection technology,the project uses relay switch instead of mechanical motion scanning switch to control the on-off switching between standard thermocouple and multiple thermocouples to be tested,so as to improve the switching rate,shorten the data acquisition time,and reduce the calibration error caused by furnace temperature change.On this basis,combined with jjg141-2013 "working precious metal thermocouple" national verification regulation technical indicators and operation process,a set of thermocouple automatic verification system is established to realize the automatic verification of Platinum Rhodium 10 platinum thermocouple and improve the verification efficiency.2.The thermocouple automatic verification system consists of two parts: hardware design and software development.In terms of hardware design,the relay switch controls the on-off of multiple thermocouples,and the digital measuring instrument communicates with the switching switch and the upper computer.The digital measuring instrument reads the thermoelectric EMF value of the thermocouple connected with the relay switch channel,and transmits the data to the upper computer through the RS-232 communication port.In terms of software,taking Windows 7 system as the carrier,visual Basic6.0 is selected to develop the software system,which realizes the functions of human-computer interaction,parameter input,automatic data acquisition and processing,thermocouple qualification determination,verification result storage and printing.3.After the development of the system,the Platinum Rhodium 10 platinum thermocouple is verified and tested,and the uncertainty of the system is analyzed.The results show that the system runs smoothly and all preset functions are realized,and the maximum expanded uncertainty(k = 2)of the system is 0.64 ℃,which is about 2 / 3 of the maximum allowable error.The measurement accuracy of the thermocouple automatic verification system meets the requirements and achieves the purpose of thermocouple automatic verification.