Hi Mahdi,
This application does suit the AD7147, it is designed to measure capacitance change.
To turn on calibration in the AD7147 it is necessary to write to the stage calibration enable register (STAGE_CAL_EN, address = 0x001). Bits 0->11 of this register are used to enable calibration for the 12 stages, set the bits to 1 to enable calibration.
The AD7147 is a capacitance controller, and it will not only measure the capacitance of your MEMs sensor, but also any capacitance around the traces connecting it to the sensor. It is very important to keep these traces as short as possible to minimise drift. In a humid environment, or an environment where the humidity is not stable, there is a possibility of drift from the sensor traces. This drift should not be very large, and it is likely that there is an issue with the setup which is causing this effect. The ideal setup should have very short traces between AD7147 and sensor, and also be in an environment where the temperature and humidity is stable.
There is no dedicated sample code for the Arduino, but I recommend that you look at the sample code provided here:
and modify it to suit your purposes.
Kind Regards,
Darragh