A digital tachometer for high-temperature telemetry utilizing thermally uprated commercial electronic components

The high-temperature environment of an oil well requires reliable downhole instrumentation, typically based on simple and robust circuits, low power consumption, and smart measurement algorithms. In this paper, we present an electronic design and measurement methodology for a simple microcontroller-based digital tachometer, optimized for downhole spinner-flowmeter applications and multichannel telemetry. We have developed and experimentally evaluated an effective algorithm for direction-sensitive rotational speed measurement, which combines quadrature pulse decoding with the method of dependent count. The algorithm employs a temperature compensation technique, making it suitable for the high-temperature application of commercial-grade electronic parts. Our results confirm the functionality and reliable operation of the tachometer, targeted at high-temperature short-term oil-well logging applications.