Lightweight Thermal Compensation Technique for MEMS Capacitive Accelerometer Oriented to Quasi-Static Measurements

Abstract

The application of MEMS capacitive accelerometers isimited by its thermal dependence, and each accelerometer must be individually calibrated to improve its performance. In this work, aight calibration method based on theoretical studies is proposed to obtain two characteristic parameters of the sensor's operation: the temperature drift of bias and the temperature drift of scale factor. This method requiresess data to obtain the characteristic parameters, allowing a faster calibration. Furthermore, using an equation with fewer parameters reduces the computational cost of compensation. After studying six accelerometers, modelIS3DSH, their characteristic parameters are obtained in a temperature range between 15 °C and 55 °C. It is observed that the Temperature Drift of Bias (TDB) is the parameter with the greatest influence on thermal drift, reaching 1.3 mg/°C. The Temperature Drift of Scale Factor (TDSF) is always negative and ranges between 0 and -400 ppm/°C. With these parameters, the thermal drifts are compensated in tests with 20 °C of thermal variation. An average improvement of 47% was observed. In the axes where the thermal drift was greater than 1 mg/°C, the improvement was greater than 80%. Other sensor behaviors have also been analyzed, such as temporal drift (up to 1 mg/h for three hours) and self-heating (2-3 °C in the first hours with the corresponding drift). Thermal compensation has been found to reduce the effect of theatter in the first hours after power-up of the sensor by 43%.

Keywords: MEMS; accelerometer; thermal compensation; thermal drift; tilt measurements.

Figure 1

Working principle of a capacitive accelerometer.

Figure 2

Axes accelerations and Euler angles.

Figure 3

Testbench used to induce the temperature variations during the tests. (a) Peltier modules with the metal plate and the heat exchanger. (b) Working diagram.

Figure 4

DUTs used during tests.

Figure 5

Orientations during the six calibration tests.

Figure 6

Exponential filter behavior.

Figure 7

Simultaneous temperature (in red) and acceleration (in blue) variations during the tests.

Figure 8

Temperature variation during the cool start test.

Figure 9

Acceleration value of the DUTs during the cool start test.

Figure 10

Values extracted for the $T{D}_{X_0}$ computing for one step.

Figure 11

$TDB$ and $TDSF$ computing from the $T{D}_{X_0}$ values (DUT #1, Z axis).

Figure 12

Filtered accelerations of DUT #1 before (in blue) and after (in red) compensation in the verification test.

Figure 13

Cool start drifts before and after compensation.

Figure 14

Euler angles before and after calibration.