The Automatic Thermocouple Calibrating System

Thermocouple is one of the most frequently-used temperature sensors in the industry. Its sensation of heat is fast and accurate and precision is high, due to directly contacted with the surroundings or object under test while thermocouple is working. When thermocouple is made from particular metal, the temperature range could be great. In addition, thermocouple usually constitutes with two or more various kinds of metal wire. It can be used very convenient with simple structure usually and the configuration which is not influenced by the size and outset. Though within such many advantages, the accuracy of measurement should be made so certain that could give great service to the people in the industrial producing process. If the accuracy of measurement could not be insured while thermocouple is using, the benefit of the manufacturers and users, even it may cause harm to person and property. So, in order to make sure the accuracy of measurement performance during thermocouple is leaving factory and being used, the thermocouple are claimed to check up periodically. The miscellaneous equipment and complicated operation are used as the universal verification method of thermocouple, requiring be watched over meanwhile, which is really inconvenient. On account of the reasons above, in this thesis, a thermocouple verification system within thin equipment, simple operation and unattended operation is planned to be designed based on researching SCM control technique and electronic measurement.In this thermocouple verification system,16bit high-speed operation MCU (Micro Control Unite) MSP430F149is the muster part. In the aspect of hardware, the system makes use of low parasitic potential relay, thus, reduce the effect of the error coming from channel switching. Using24bit high resolution ADC (Analog To Digital Change)IC AD7714, the minimum stepping voltage is0.2uV can meter the change of thermocouple more accurately. Using TET color screen for data display can unattended operation and off-line working come true. On the software of this system, realize accuracy controlling of furnace temperature through using PWM mode and stability controlling of furnace temperature through using PID feedback control algorithm. A variety of thermocouple calculated coefficients are preset within software. Only artificial selection of thermocouple types is required when checking up different thermocouples, so that automatic temperature control verification can proceed. The system work out the verification result of thermocouple and can judge the thermocouple by verification and human-computer interaction re-inspection automatically. Moreover, the system comes with the function of serial communication which can be connected to PC for data communications in necessity. At ordinary times, the system can also stand alone work in using process which reduces costs of the whole system.