Development of an optical displacement transducer for the measurement of soil surface profiles

Abstract The transducer is a fast response opto-electronic displacement monitor with a working range of ±150 mm about a point 600 mm from the sensing head. Although developed for the measurement of soil surface profiles, the transducer will operate on any diffusely reflecting surface. The device collects light from an illuminated spot on the target surface and focuses this on to a position-sensing photodiode, giving an output related to the position of the target. The signal-conditioning circuitry discriminates against the effects of ambient light and compensates for changes in surface reflectivity; a simple technique is included to give an output directly linear with distance. The frequency response is flat up to 40 Hz.