Ultra Precision Temperature Measurement And Control System

The successive development of electronic technology promoted the rapid development of other related fields. Especially measure and control system on basis of electronic technology has burgeoned with the passage of time. Temperature is a basic physical quantity which scientists have sustained the research of temperature measure and control, whereas normally it would be researched in degree Celsius, barely accurate to centi-degree Celsius, hardly to mili-degree Celsius.The research object in this article is the calibrating apparatus for temperature measure and control instrument, therefore it requires a higher accuracy than in daily life and in elementary industries. The experimental standards are as follows:Resolution:0.001 ?, Stability: ±0.003?, Range:0?-100?. The difficulty of the manipulation lies in a high level of accuracy in measuring and controlling of the temperature.On the realization of high precision temperature measurement, the methods of this paper using are as follows. In the design of precision constant current source circuit, with high precision, low noise current through Pt1000, thus produce strictly voltage with temperature changes. And using a high precision measurement circuit collects voltage value to get the corresponding temperature value. During the designing of the constant current source, first, use a high precision voltage reference circuit to obtain high precision voltage, then design a V-I transform circuit to obtain constant current. Pt1000 uses four wire cable to connect with constant source and the measuring circuit respectively. In the measurement circuit, obtain the voltage value after differential transform them at both ends of Pt1000, then use the acquisition of high resolution ADC.The method of realizing the temperature control is as followings. Control the refrigerating capacity by controlling the size of semiconductor cooler's voltage so as to realize the controlled object's temperature. TEC's both terminals gets the voltage of the PWM wave after power amplifier and low-pass filtering. Voltage control is completed by adjusting the duty ratio of PWM wave. In order to realize high precision control, this paper fully studies from PWM power amplifier to the waveform error in the process of impact, and analysis of dc voltage ripple and noise after filtering etc.The control of the whole system applies LM4F123GH6PZ micro controller of the Texas Instruments Corporation to complete the control of the circuit, the PWM wave generation, data processing and the processing of human-computer interaction.In order to ensure the realization of high precision, this paper fully consider:the possible error and noise from the electronic device, the distribution parameters of the circuit of signal, the influence of various signal delay and the error influence, the noise to signal caused by the unreasonable PCB layout in the process of circuit design. For the sake of improving the system accuracy, the circuit boards involved in this paper have adopted a variety of noise reduction processing, to avoid the noise caused by unreasonable layout as much as possible.This paper uses the digital PID control algorithm to control temperature. After theoretical research and a large number of experiments, I obtain the appropriate P, I, D parameters, and make sure the system can realize the high precision temperature measurement and control.