
Shaft Speed Switches
A speed switch senses rotating shaft speed, comparing it to one or more settable over/under/zero speed alarm trip-points. A shaft speed sensor detects magnets embedded in a shaft-mounted pulser wrap/disc. As the shaft rotates, the passing magnets are detected across an air-gap as pulses with frequency proportional to shaft RPM. When a conveyor belt or bucket elevator begins to slip the pulse frequency (shaft RPM) crosses to the alarm side of a trip-point threshold, a corresponding relay de-energizes, providing shutdown or alarm.