Zero Speed Switches

Zero speed switches are suitable for detecting the absence or presence of motion of rotating, reciprocating or conveying equipment. Thus, these speed limit switches can also provide an indication when the system is at rest. A suitable motion detector probe is provided depending on the application.

The system comprises of a suitable motion detector probe and electronic circuitry for
detecting zero speed. The circuit consists of a step down transformer, a rectifier, a filter and a DC regulated power supply. It consists of a delay circuit that provides starting time delay and a re-triggerable timing circuit, which compares the time between two pulses with a fixed time duration. The sensor circuit senses the moving target and outputs pulses, whose frequency is proportional to the speed of moving target. Adequate cable entries are provided for wiring.

The speed switches can work in a broad range of temperature with -20°C as the lowest and +60°C being the highest temperature point. The zero speed can be set from 3 ppm (pulses per min.) to 20 ppm.

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When power is initially applied to the zero speed switch, the alarm relay is energized and held by the timing circuit for desired (settable) time duration. Whenever the motion detector sensor detects a target, a signal in the form of pulse re-triggers an internal timing circuit. This action keeps the alarm relay energized providing a fail-safe operation of the contacts. If no target is sensed for desired time duration (that is settable), the timing circuit will not be re-triggered. This will cause the alarm relay to de-energise and the contacts to change state. Thus the relay output contact can be used for signaling / controlling.

Mechanical Specifications

Cable Entries

  • 2 nos.

 Operating Temperature

  • -20°C to +60°C


  • Cast aluminium, weatherproof Stoving enamel painted


  • By potential-free N.O. contact of contactor controlling the motor of
    the monitored equipment

Start-up Time Delay

  • 3 to 20 seconds

Zero Speed Time

  • 3 ppm to 20 ppm
Electrical Specifications


  • 110 / 230 V AC (-10 to +10%) 50 Hz (as specified in the order)


  • One relay with a set of potential-free c.o. contact rated at 6A, 230 V
    AC, 50Hz for non-inductive load


Application Specifications

Zero speed switch is suitable for detecting the absence or presence of motion of rotating, reciprocating or conveying equipment.

Switching Indication
  • 3 LED’s
    • Red: Alarm (relay de-energized)
    • Green: Normal (relay energized)
    • Yellow: Pulse Detection