Optimal Design Of Measurement And Control System For High-precision Constant Temperature Cabinet

It's important to control the surroundings temperature seriously to make sure the high-precision measuring instruments can work under natural conditions and work effectively. In this case, the design of the original temperature measurement and control system is optimized to improve the precision of the temperature controlling, minimize the transition time of the temperature controlling, and reduce the hardware cost base on the constant temperature cabinet.This paper focuses on the high precision temperature measuring technology. The thermal and electrical nature of the NTC thermistor is introduced firstly. By re-calibration and modeling, the thermistors have the accuracy of 0.01℃between 18℃~22℃. Then a kind of multi-channel temperature measuring method using analog multiplexers with high performance is proposed based on the thermistors The uncertainty because of the constant-current source on the final accuracy is eliminated by using comparatively measuring. In the end the hardware & software design is presented totally. The experiments show that the accuracy of the temperature measuring system can be up to±0.02℃, with the resolution up to 0.001℃in 18℃~22℃.The cabinet is modeled mathematically by using the second order subject without delays through system identification. In this case, it discusses the PID control theory in the temperature controlling system and introduces the digital PID control algorithm. As in compare, the theory of fuzzy control is introduced and a fuzzy controller is designed. A fuzzy-PID strategy is adopted by comparing two control schemes through simulation. Finally, a new measuring & control system is established and studied experimentally. The results show that the temperature fluctuation of a single-point is±0.02℃, the transient time is less than 8000 seconds and the desired objective has been met.