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 are 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 (1 μm 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 system´s 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.