HIGH PRECISSION OPTICAL POSITION SENSOR FOR ELECTROMAGNETIC FORCE COMPENSATED BALANCES

Christian Diethold, Thomas Fröhlich, Falko Hilbrunner, Gerd Jäger

Abstract

This paper discusses an optical position sensor which can be used in balances based on the principle of electromagnetic force compensation (short used EFC) for example. Other applications are zero point detection as well as high precision positioning in the range of ± 200 &#956;m. The position sensor consists of two infrared-LED (IR-LED) which illuminate a single photodiode via an aperture. The aperture is movable and performs a shadowing of the beams, thus shadowing changes due to the position of the aperture. The photodiode detects light from both LED. Both light sources have to be modulated and phase shifted to distinguish them in the photodiode signal. The evaluation of the position of the aperture is done by demodulating the received signal. <br />A major advantage of this method is that the aperture's operating point is in the centre of the beams. Hence higher sensitivity is achievable and the beams can be focused onto the photodiode. Furthermore standard components are used and thus expensive differential photodiodes are no longer necessary.

Keywords

position sensor, zero point detection, balance with electromagnetic force compensation

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IMEKO TC

TC3 - Measurement of Force, Mass, Torque, and Gravity

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