| The constant temperature bath is a verification device that provides a temperature field environment and is used to verify standard platinum resistance,instrumentation and other equipment.The performance and accuracy of the constant temperature bath affect the measurement results and determine the work quality of the metrology industry.Analysis of most domestic thermostats shows that their temperature control accuracy is low and the temperature control effect is poor.Although it can meet the needs of users to a certain extent,the resolution of the temperature control instrument is low and the singleness of the temperature control system cannot be very good.Well meet the needs of the market.In addition,in some PID control processes,there will be some phenomena of long temperature control time and temperature overshoot,which will have a certain impact on temperature measurement.In order to meet the requirements of national standards,improve the influence of temperature control accuracy and the defects of PID control,a rapid temperature rise and fall thermal resistance verification constant temperature tank is designed,which greatly improves the temperature control speed,and adopts advanced BP neural network PID control.The method improves the temperature control accuracy of the constant temperature bath.The specific research content of this paper has the following parts:（1）The whole structure of the rapid heating and cooling thermostatic bath is designed.Aiming at the problem of the temperature control accuracy of the constant temperature tank,according to the basic law of heat transfer,a rapid temperature rise and fall constant temperature tank is designed,the main working principle of the constant temperature tank is expounded,and the overall structure of the constant temperature tank is designed.Research and design of key components such as main tank,auxiliary tank,and liquid circulation device are carried out,and relevant design parameters are determined.（2）The main circuit inside the thermostatic bath is studied.According to the basic functions to be realized,the layout design of the whole circuit of the thermostatic bath and the drawing of the circuit schematic are completed.According to the design requirements of the thermostatic bath circuit,the corresponding electronic components are selected,and the parameter values of the electronic components are determined.Through the connection between electronic components and microprocessors,software control is performed to complete the control of each component.（3）A PID high-precision temperature control system based on BP neural network is constructed.According to the temperature control accuracy requirements of the constant temperature tank,the BP neural network algorithm is introduced to optimize the PID parameters.The traditional PID control algorithm,Z-N self-tuning algorithm and BP neural network PID control algorithm are expounded,and the simulation of the three algorithms is completed.The advantages and disadvantages of the three control algorithms are analyzed,and the superiority of the BP neural network PID control algorithm is determined.（4）The temperature field uniformity and stability experiments of the thermostatic tank prototype were carried out.According to the requirements of the national regulations,a temperature field test system for a constant temperature bath was built to test the uniformity of the axial temperature field,the uniformity of the vertical temperature field and the equipment stability of the constant temperature bath.The experimental results show that the maximum fluctuation of the constant temperature bath is 0.018℃/ 10min;the maximum temperature difference under the horizontal temperature field experiment is 0.005℃;the maximum temperature difference under the vertical temperature field experiment is 0.007℃.In line with the national JJF1030-2010 thermostatic bath technical performance test specifications,and better than similar products. |
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