Digital phase sensitive rectification of ac driven transducer signals

Abstract

A method and a system for phase sensitive rectification of signals from transducers driven by an AC excitation signal will be disclosed. The method and system demand a very moderate calculation capacity, thereby to facilitate the use of low cost microprocessors of ordinary speed. The present method and system utilize a sampling being synchronized with the transducer excitation frequency f. Sampling of the sensor signal is performed by an A/D-converter at a high sampling frequency, nf. The sampled signal then is averaged over half a period of the excitation signal frequency, whereby the starting point of the averaging is decided by the time of commutation. This is equal to filtering the sampled signal by a decimating filter. The rectification may then may be preformed with a number sequence sampled by the optimal sampling frequency 2f (twice the excitation frequency only) instead of the sampling frequency nf used for obtaining high resolution. The output then is further filtered by means of a digital filter acting as an ideal low-pass filter as well as an output filter for achieving a desired output signal level. The signal output will be then be simply made available for further digital processing. However, the output still offers high resolution measurements in spite of only demanding moderate speed microprocessor capacity for the processing.