Research Of Temperature Correction Technique For Force-balance Accelerometer

Accelerometer is the key part of strong motion networks, whose performence can affect thequality of strong motion observation. The feed-back and force-balance technique is widely appliedto achieve the goal of wide work frequency band, high dynamic range, and low self noise. Theaccelerometer with feed-back and force-balance technique is called force-balance accelerometer,which is widely used in strong motion observation system.Force-balance accelerometer has lots of advantages, but some parameters, such as sensitivityand zero-level drift, may be influenced by the surrounding temperature. And it will increase thecost of utilizing and maintenance of accelerometer, make the instrument less stable, and lower thequality of strong motion records. In this paper, our research object is the force-balanceaccelerometer. Our purpose is studying the method of tempreture correction, decreasing thezero-level drift, improving the thermal stability, and making the quality of strong motion recordsbetter.The core ideas of this paper are to build a low zero-level dirift reference, and using thisreference to compensate the affection of tempreture, decreasing the zero-drift level ofaccelerometer to the level of reference.MEMS accelerometers are sigel chip accelerometer using micro mechanical and electronictechnique, which are widely used in vibrational detection scope and precision instruments.Although the self-noise and dynamic range of MEMS accelerometer is worse than force-balanceaccelerometer, there are still some unique advantages, like small size, low power consumption,and so on.In paper, we design a mini thermal stable system with lower power consumption and simplestructure, which can keep the temperature surrounding MEMS accelerometer constant. Then wecan get a low zero-level dirift reference.According the different characteristics of two accelerometers, when we integrate the system, weneed to design a low-pass filter to restrain the influence of noise from MEMS accelerometer toforce-balance accelerometer, so the correction only happens in low frequency scope. Referring to frequency scope of seismic waves, application of accelerometer, noise comparation, and variationof tempreture, we determine the parameters of LP filter. And then we need to design digitallow-pass filter to complete our program. So in paper, we build a tempreture correction system withADC circuit, CPU circuit, and DAC circuit.We have to test the sensitivity and angel error of two accelerometers before correction work,and use the test result to update the correction value. So we use gravity method and rotationalplatform to get these parameters.After we finish our plan, we build hardware supporting system and embedded software system.The hardware system includes: force-balance accelerometer system, MEMS accelerometer withmini thermal-stable system, and tempreture correction system. The software system is developedin chip with ARM7core, which can control the operation of digital signal processing system, getthe real-time correction value.When all the work completed, we test the performance of new instrument, the result shows:1. The max power consumption of mini thermal-stable system is about0.37W, and it can worksduring a tempreture scope of50℃. In working range, the tatio of inside and outside tempreturevariation is less0.1%. The zero-level drift of MEMS accelerometer with mini thermal-stablesystem changes from0.5mg/℃to below0.1mg/℃.2. The zero-lever drift of force-balance accelerometer after correction changes from higher1mg/℃to the zero-level drift of thermal-stable MEMS accelerometer.3. After the self-noise test of accelerometer, we recognize that the tempreture correction systemcan make the noise of low frequency scope more flat, and increase the noise level very small inhigh frequency scope.To conclude, the tempreture correction maitioned in paper can greatly improve the zero-leveldrift of force-balance accelerometer, and make a little influence to the self-noise. As while thefunction of instrument extends widely because of using the digital signal processing system.