Ultrasonic micrometer position indicator with temperature compensation

This paper discusses a novel ultrasonic system for high precision relative position monitoring. An innovative combination of existing signal processing techniques was implemented to facilitate an accurate, efficient, and automated digital algorithm. A method was derived for physical compensation of temperature dependant water velocity through the design and use of a two-tiered target. A leave-in-place, couplant free transducer was designed and fabricated for use at elevated temperatures, the details of which will be discussed in presentation form. A prototype was developed according to wave propagation principles in order to produce multiple roundtrip reflections from a water immersed target. The digital automated processing included gate tracking algorithms, reference correlations, and Hilbert transformed envelopes which helped facilitate a phase stability of 1-3ns. This allowed for a precision of λ/150 (1μm at 10 MHz) in relative target positioning. Analysis was conducted at 23°C and 77°C with velocity measurements taken over this range in order to qualify the systems capability of position indication at elevated temperatures. Repeated target movements on the order of 100 μm were measured with approximately 0.1% mean square deviation from average over a displacement range of 1mm at both temperatures.