Development of a contactless displacement transducer

A displacement transducer is described which enables changes in the distance between itself and an unprepared surface to be measured without physical contact. An optical system is employed. The transducer has a resolution of 0.25mm and measures over an interval of 15mm centered at a distance of 270mm from the sensor beam. The transducer's accuracy is within +- 0.25mm. A second transducer is mentioned which will measure over a range of 72mm. Both transducers sample the position of the surface over a time interval of 200 nanoseconds with a minimum time between obsevations of 200 microseconds. Alternative configurations are presented giving different characteristics. The transducer has been developed as part of a high-speed-profilometer system for measuring the longitudinal profile of pavements. Texture depths of pavement surfaces have also been measured using the transducer. The transducer is suitable as the basic unit of many displacement measuring systems where the response advantage of an inertiafree transducer or the absence of physical contact is important.