RPM / FREQUENCY Limiter Switch

HewTech Electronics LLC has developed a LOW-COST, low component count RPM / FREQUENCY limiter switch.


Model RLS -10 has 2 individual / adjustable RPM / Frequency set-points. Relay remains in a de-energized condition until the calibrated threshold is exceeded. Once exceeded, the over-speed LED illuminates, the relay is energized and changes state. Relay de-energizes once the RPM or Frequency has reduced below the calibrated set-point. Relay is 10A SPDT and can be connected to motor control relays, kill-switches, alarms etc.

Rotation pulses are monitored through any industry standard inductive proximity switch (NPN-type), however almost any “current sinking” configuration is compatible. Typical upper RPM range is 7000 RPM’s ~ 50,000 RPM’s, with 1 pulse per rotation. Additional pulses per rotation, such as spokes or gear-tooth will allow much lower RPM’s. Minor changes to circuit configuration will allow unlimited range possibility.

Typical uses include over-speed governor control on motors, fans, mixers, conveyors, grinders, blowers, generators, engines and other critical speed-sensitive devices and applications.

Power is 12 volts DC @ 2-watts. Board dimensions are 2″ x 3″, with (4) #6 mounting hole positions.

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