Research And Implementation Of High Precision Temperature Measurement And Control System

Cement hydration heat is one of the important parameters of cement.In order to choose the right cement for concrete construction,the hydration heat of cement must be accurately measured.Because its measurement process is very sensitive to changes in external temperature,therefore,it is necessary to focus on how to provide a high-precision constant temperature environment for the calorimetric process,so that the measurement results have a high accuracy.This thesis firstly proposes the overall design idea for realizing a high-precision constant temperature environment,and designes a precision gas bath thermotank from the structural aspect to reduce the influence of the external environment.The temperature field in the thermotank is obviously nonlinear,which is affected by the external temperature change,the air convection in the box,and the working power of the heating or cooling elements;In addition,the temperature control of the thermotank also has hysteresis,which makes it difficult to determine an accurate mathematical model;There is also a high-precision requirement of ±0.02℃ temperature fluctuation in the thermotank,which has increased the difficulty of temperature control in the thermotank.Based on the above-mentioned conditions in the thermotank and high-precision control requirements,the system uses the STM32F103 chip as the main controller,and designs and realizes various modules,such as temperature measurement,temperature control,heating or refrigeration and other links.The software part of the control system is realized on Keil platform using the embedded operating system μC/OSII based on C language.The control algorithm uses the algorithm combining BP neural network prediction module and fuzzy PID control,and establishes the corresponding controller.Aiming at the hysteresis of temperature control of the thermotank,the temperature change rate is used as one of the inputs of fuzzy control,which is predicted and calculated by the BP neural network from the external environment temperature,so that the controller have the effect of advanced control.According to the temperature change,the controller can regulate the three parameters of PID on the basis of the fuzzy control rules to achieve the purpose of adapting to a complex and changeable environment.Both the control effect and the control accuracy have been improved.Finally,perform related performance test experiments on the established thermotank temperature control system.The experimental results show that when the outside temperature fluctuates <3℃(<5℃),the temperature control accuracy in the thermotank is ≤±0.013℃(≤±0.02℃);At the same time,the measurement result of the cement hydration heat has high accuracy.It proves the rationality of the control algorithm based on BP neural network prediction and fuzzy PID used in this paper,and the stability of the designed high-precision thermotank temperature control system.