Proximity Sensing

Abstract

Earlier chapters of this book dealing with position sensing have dealt only with the continuous measurement of the position of an object within a given range of movement. There are many applications for some much simpler ‘go-no go’ measurement. For these the output is a single bit of information which indicates that the object has reached or passed a particular position. Where adequate power is available a mechanical switch may be used, operated by pressure from the moving object, as in the ‘over-ride’ switches often fitted to lifts as a safety measure. Similar arrangements may be used in which a swinging arm operates a micro-switch for sensing that the paper in a printer has run out, or the end of the tape has been reached in a tape recorder.