High resolution adaptive tachometer for spindle motor drives

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Abstract
A high resolution tachometer device is described which can monitor transient speed changes of the order of 0.1% centred around a steady-state, nominal speed in the range 12 · 56 to 209 · 44 rads−1. Unlike existing designs, the unit employs electronically adjusted pulse counting to maintain a constant percentage error over a wide speed range. The device is microcomputer based and includes an optical shaft encoder and a custom developed interface card. The counting mechanism is totally hard-wired to minimize the sampling time. Furthermore, inexpensive hardware addressed by a software program makes the entire speed measuring process automatic and virtually instantaneous. Tests have shown the device to possess a better response time than previous designs.

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