A comparative study of gravitational acceleration cancellation from on-rotor MEMS accelerometers for condition monitoring

There have recently been significant enhancements in Micro-Electro-Mechanical Systems (MEMS) technologies, which have provided an easier and cheaper means of condition monitoring for rotating machines by installing MEMS accelerometers directly onto rotors. One critical issue in using on-rotor MEMS accelerometers is extracting the real tangential acceleration from accelerometer outputs which also contain gravitational acceleration. This paper studies and compares two different methods that can be used to eliminate the gravitational acceleration so as to characterise the rotor dynamics precisely. In the first method, the pure tangential acceleration is reconstructed by combining two orthogonal outputs of a single MEMS accelerometer attached to the rotating part. The second method uses two MEMS accelerometers mounted diametrically opposite each other on the reciprocating compressor flywheel, allowing the gravitational acceleration signal to be cancelled by summing the acceleration signals from both sensors. Based on analytical and experimental results, gravitational acceleration can be successfully eliminated by both methods, and the calculated tangential acceleration signal can effectively reflect the running status of a reciprocating compressor subject to the leakage fault.