Subminiature Inductive Transducers used with High Carrier Frequencies

Abstract

This paper describes the development and construction of subminiature inductive transducers which can be operated with carrier frequencies up to 400 Kcs. Two types have been developed for operation at 150°C which are able to withstand an acceleration of 2000g, and a high-temperature (600°C) transducer is now in the final stage of development. The body of the low-temperature transducer is made of high-temperature epoxy resin, and that of the high-temperature transducer of ceramic material. Iron wire is used as core material to reduce eddy current losses. The dimensions of the transducers are 0.25 inch diameter and 0.5 inch long, and 0.125 inch diameter and 0.25 inch long, including terminations. A linear displacement of the armature material can be measured at distances up to 0.01 inch, and because of the high carrier frequency, the vibration of this armature can be up to 30 Kcs. Both ferrous and non-ferrous armature material can be used for displacement measurement. The inductive transducers have been used to measure piston movement at right angles to the cylinder axis in an internal combustion engine, in conjunction with a lead-out system. Tests using a telemetry system (radio link) are now being carried out. Details of the construction and performance are described and future development discussed. The use of the inductive transducer as a pressure transducer is also mentioned.