Comparison of Incremental Encoders in Order to Improve IAS Based Diagnosis

All PHM strategies are based on scalar or vectoral indicators that translate more or less synthetically the statistical properties of the measurements made on the machine to be monitored. The physical signals measured can be of various kinds. In the particular case of rotating machines, vibration monitoring based on accelerometer readings undeniably dominates the market. However, other physical measurements may reveal faulty behavior. This paper is interested in obtaining monitoring indicators based on the measurement of the instantaneous speed of a machine. Just like the monitoring of electric current, acoustic, thermal and sound emissions, the analysis of the instantaneous speed offers a new angle of view on the behavior of the machine and has already proven itself in the first cases. The sensor used to obtain this signal is most often an incremental encoder. There are various technologies available, from the robust and inexpensive phonic wheel, to high-resolution optical encoders, or else zebra tape glued on a shaft... The aim of this paper is to study the influence of the quality of an encoder on the ability of the monitoring indicators that will be deduced from it to detect defects of all kinds.