In this paper, an improved method is presented to derive the velocity information in a pulse-number measurement/time-duration-type digital tachometer by processing its pulse train. The method incorporates encoder pulse counting and very accurate time measurement. The velocity sampling interval is not constant but is continuously modified. An adaptive algorithm provides a wide-range velocity evaluation with very good accuracy. The adaptation of the next sampling period, according to the instant velocity, results in better response times at low speeds and a very high accuracy at medium and high speeds. Compared to currently known methods, the time measurement resolution and, consequently, the velocity accuracy is improved by using the proposed method due to the inclusion of high-resolution time-to-digital converters in the design. The proposed configuration can be implemented in specific hardware by using field-programmable gate arrays (FPGAs), thus saving the computational power of the digital signal processor that supervises the system for higher level control tasks.
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