Zero speed switches, operation, application, advantages

There are different speed monitoring devices used in the process industry, a speed monitoring device is useful to give an alarm or to turn off the engine. In the case of closed-loop control.

What are zero speed switches?

Zero speed switches (ZSS) also known as Speed Actuating Sensing Switches. The zero speed switch detects the stoppage of rotating shafts. This switch is designed to detect zero speed (speeds less than 1 RPM) of the monitored shaft. Mainly used in application such as a conveyor, power plants, and industries involving the production of cement, sugar, textiles, paper, etc

Principle of operation:

The basic principle of speed monitor is a comparison of pulses received from the sensor with standard pulses. The unit consists of two parts: control unit and “sensor probe”.

The sensor must be installed with its detection face near the rotating object. In this object, the flags must be set. The sensor produces strong electromagnetic waves, which are disturbed by the flags, giving rise to corresponding pulses. These pulses are sent to the control unit where they are compared with the standard pulses to detect the speed.


The zero speed switch receives the signal from the proximity sensor. When the speed of the input signal is above the set speed, the relay is activated/deactivated. When the speed drops to zero, the relay turns OFF / ON. It can be applied to trigger the system or give a warning signal.

Proximity Sensor senses rotation of the roller and gives pulses to control unit. Output relay is actuated when incoming pulses from proximity are stopped.

Initial time delay &; nuisance delay:

Initial time delay facility to allow the rotating mechanism to attend the desired speed is provided. Standard delay is 0-30sec. Nuisance delay allows the system to delay the trip action for few seconds as it may recover the speed.


Steel plant, Thermal power station, Tiles factory, fertilizer plant, blowers for heating system, coal factory, cement factory, food industries, textile industries, Automobile industries etc.


  • Detect speed without contact Therefore there are no moving parts.

  • Intrinsically safe sensors and speed switches with flameproof boxes are available for use in hazardous areas.

  • No wear and tear of the rollers or misalignment of the couplings.

  • Easy adjustment of the speed.

  • Built in the initial by-pass time delay layout

  • Possible speed adjustment from 1 RPM to 5000

  • RPM in optional ranges.

  • Fully closed sensor, works in the presence of dust, dirty water, oil and chemicals.

  • It is possible to detect the direction and control the speed of several locations from a single point.