Optical tachometer
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The 2618 optical tachometer, made by Graham and White Instruments, is said to be particularly suitable for measuring the speed of electric motors, diesel engines, pumps, turbines, textile machinery and so on. Because a non-contact system is employed, use of the instrument enables many installation and servicing problems associated with conventional mechanical or electrical systems to be overcome.
A beam of light up to 36in. long is projected onto the rotating component under investigation. A piece of reflective paint, or tape, is attached to the rotating component and at every revolution the beam is returned as a pulse of light. These pulses are counted (digitally), to give an exact indication of linear or rotational speed. Alternatively, the pulses can be converted into an analogue signal which can drive a moving coil meter or digital volt meter to measure speeds from 50 rpm to over 100,000 rpm.
Made by: Graham and White Instruments, 82 London Road, St Albans, Herts.