In many designs where position is critical but space is not available for conventional long-stroke sensors such as LVDT's, short-range high-resolution inductive sensors may provide the solution. An example would be measuring the position of a leadscrew-driven elevator assembly in an automation process line. The stroke is 10 inches and the desired positioning precision is 10 mils.
By using a digital sensor system, digital alarm outputs can be set up for upper and lower position limits.
Using a digital, dual-channel, inductive linear-displacement sensor, set up to measure thickness, provides the solution. By mounting the two sensors looking at opposite sides of a tapered aluminum target, and setting up the sensors to derive thickness, linear position of the elevator platform can be determined.
With a target that tapers on both sides from 1- to 0.5-inch thickness over the 10-inch range, a system with two sensors calibrated over a 0.25-inch range, with 0.08% FS resolution, would provide vertical position resolution of less than half a mil—well below the desired position precision of 10 mils.
Dan Spohn, Kaman Instrumentation Corp., 3450 North Nevada Ave., Box 33010, Colorado Springs, CO 80933-3010; Tel: (719) 635-6982; Fax: (719) 634-8093; E-mail: firstname.lastname@example.org.
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