The Development Of Thermostatic System For Airborne Gravimeter

Airborne gravimeter has a very wide application in geologicalsurvey, oilexploration, mineral exploration and other fields. Accelerometer as the core of theairborne gravimeter sensor, its resolution, accuracy and stability determines theaccuracy of measurement of the airborne gravimeter, the accelerometer zero bias andscale factor is strongly influenced by the temperature. Therefore, thermostatic Systemcould ensure the accuracy of the airborne gravity. This design objective is complete thetwo levels of temperature control system for the accelerometer to ensure work inconstant temperature that RMSE below0.01℃, thus ensuring gravimetermeasurement precision can reach0.5mGal.Thermostatic System that includes two levels of temperature control, hardware,software and test platform composed the system..Hardware part includes temperature measuring circuit, heater circuit, powercircuit. Temperature measuring circuit Temperature measurement circuit containseight temperature measuring points, and using four arm bridge circuits via the PT1000platinum thermal resistance temperature sensors to obtain voltage difference, thenthrough the input voltage follower to24AD converter which link to STM32F103withSPI for data processing,. Heating part consists of two digital analog PID heatingcontrol circuit and two digital heating control circuit. Using nickel chrome wire heatto two levels of system. Analog control using PT1000platinum thermal resistance toobtain temperature with wheat-stone bridge independently that control the switch ofMOSFET, that could ensure reliability through subsequent precision comparison,filtering, PI regulation and such as processing. Digital heating control circuit receivesthe STM32output PWM wave, then through the comparator and MOS switch controlheating frequency, that could ensure high precision and prevent over shoot. The powerpart converts the external input28V to+9V voltage with DC/DC module, and then to subsequent voltage conversion. Power supply section provides6stable voltageoutputs, the maximum power about30w.The core of the software part is STM32processor that could acquisition andprocessing temperature, then enforces precision temperature control for Secondarytemperature control system, realize the permanent preservation, touch display of thedata, and serial port communication functions.Constant temperature platform composed of red copper and stainless steelprocessing, inside has two levels of the platform, each level use two way nickelchrome heating resistance wire winding and keep warm. There have four L-shaped viato communicate with external control system in the base of the constant temperatureplatform for reduce the cooling as far as possible.Thermostatic system under the environment of indoor and outdoor test results asfollows: in the environmental temperature18℃(Peak value), constant temperatureprecision of0.0098℃(mean square error), and is superior to the design target.