Reluctance Pulse Pick up Transducer:

This Reluctance Pulse Pick up Transducer is very suitable for the measurement of shaft speed and liquid flow. It is based on the principle that if the field of any magnet is varied momentarily by the motion of an external magnetic body near it, a voltage pulse is generated at the coil of the magnet because of the change in flux surrounding the coil. The Reluctance Pulse Pick up Transducer consists of a permanent magnet on which a coil is wound.

The output voltage depends upon the rate of change of magnetic flux and the number of turns. Flux depends upon the clearance between the pick up and the actuating medium, the rate of movement and size of the actuating medium. The output voltage is inversely proportional to the distance between the head of the pick up and the actuating medium.

The pick up is actuated by the teeth of a gear or blades of turbines. In rpm measurement, the pick up is placed near the teeth of a gear. The motion of the gear tooth distorts the magnetic field around the core magnet.

A voltage pulse is produced every time a tooth enters or leaves the area of the pick up coil. The frequency of pulse is then proportional to the speed of the gear. This can be used for a tachometer.

Similarly, a pick up can be used to determine the flow, as the speed of the turbine through which the liquid flows is proportional to the flow. The total pulses counted are proportional to the total flow.