Design And Implementation Of Digital Temperature Control System For Accelerometer In Gravity Gradiometer

Rotating gravity gradiometer can measure the second order gradient of gravitational field,which is of great significance to applications,including geophysical research,resource exploration,and national defense force.High-precision accelerometers are the core component of a gravity gradiometer,and its measurement accuracy directly affects the measurement results of the gravity gradient.It can be concluded from previous studies that the change of temperature in the working environment of the accelerometer will affect its output,thereby limiting the measurement accuracy of the rotating gravity gradiometer.Therefore,it is necessary to develop a high-precision temperature control system for the accelerometer and the entire gravity gradiometer.This thesis investigated,designed and implemented a preliminary second-stage digital temperature control system,intended for rotating gravity gradiometer developed by our research group and,where a three-level temperature control scheme is proposed.The system uses the negative temperature coefficient thermistor(NTC)to measure the temperature,then calculates the control value through the digital PI control algorithm using the digital signal processor(DSP),and finally drives the thermoelectric cooler(TEC)to control the temperature of the accelerometer shell.The design purpose of the second-stage digital temperature control system is to provide a stable environment temperature control for its internal first-stage temperature control system which is designed for the accelerometer structure,and enhance the control precision of the first-stage temperature control system.Based on the above temperature control scheme,this thesis has completed the design and implementation of the second-stage digital temperature control system,including hardware circuitry and software algorithm.The hardware includes three modules: DSP circuitry,temperature measurement circuitry and TEC drive circuitry.The software algorithm is developed using C programming language with Code Composer Studio(CCS)for development environment,which mainly accomplished the functions of temperature signal acquisition and processing,digital PI control algorithm,and ultimately generating control quantity output.After the joint test of system’s circuits and software,the second-stage digital temperature control system test equipment was set up which simulated the three-level temperature control system,including the external temperature box that simulates the thirdstage temperature control system,and the internal heat source that simulates the first-stage temperature control system.In the process of testing the system,we found that the single-channel TEC control has insufficient heat dissipation,which led to heat accumulation,ultimately causing the system instability.In order to solve this problem,we proposed to increase the TEC heat dissipation area and the number of TEC.The proposed approach alleviates the problem.The final test results show that under the condition of the first-stage and the third-stage temperature control system,the second-stage digital temperature control system designed in this paper has a temperature fluctuation of 0.005 ℃@12 h in the steady state,which meets the system design requirement of ΔT ≤ ±0.01 ℃.