Control System Instrumentation

What is a zero-speed switch?

A zero-speed switch is used in conveyors, motors, and it is also used to detect the rotating shaft speed. A zero-speed switch is used in conveyor belts and it would stop the conveyor if the speed of the belt falls below the set speed. These switches would trip the motor circuit if the motor is running and the conveyor belt does not. It can detect the jamming or slow speed of the motor shaft so it would stop the motor. A zero-speed switch would have a sensor and a controller. The sensor would sense if there is any trouble like slow speed and it would send a signal to the controller. So according to the received signal proper action will be taken by the controller.

What are the major parts of a zero speed switch?

  • Inbuilt relay
  • Indicating LED
  • Voltage supply terminals
  • Terminals for the NO and NC contacts of the relay
  • Terminals to take the input from the sensor
  • Electronic circuit
  • Speed adjusting knobs

How does a zero speed switch operates?

The operation of the zero-speed switch utilizes the electrochemical, electronic, or magnetic effect. So this switch would operate by means of any of the following effects.

Conveyor

In a conveyor a zero-speed switch is placed near to its end, the studs of the conveyor will be welded together at a certain angle difference. The proximity sensor would sense these stud parts during the rotation of the tail pulley it would sense it and sends a signal to the controller. The speed of the tail pulley would be determined by the controller and they would check this speed continuously. So if the speed reduces below the set value, the relay contact of the controller would drop, and thus its contact will be changed and its feedback is used to trip the motor circuit.

Motor

This switch can be used to detect the slow speed of the motor shaft. The sensor would sense the shaft rotation and sends pulses to the controller. So if the rotation speed varies the relay will be actuated and it would break the output circuit after setting time delay. This switch can protect the motor in case if the screw is overloaded.

What are the advantages of a zero speed switch?

  • It operates without any contact with the machinery so there is no moving part and thus less maintenance
  • There won’t be any wear and tear of the roller or misalignment of the coupling
  • Speed setting is simple
  • It has a built-in initial bypass time delay arrangement
  • The sensor is totally enclosed, so this device can be used with dirt, dust, or chemicals
  • Safe sensors with enclosure types can be used in hazardous areas
  • It can determine the direction and speed of different locations from a single point

What are the applications of zero speed switch?

  • Speed monitoring of conveyor
  • Industrial machinery speed monitoring, machineries like crushers, rolling mills, mixers, stirrers, and a lot more
  • It can be used to actuate the relay contacts at a preset speed, by using these contacts certain control actions such as zero speed protection, under-speed protection, and over-speed protection can be achieved.
  • It is used in many industrial manufacturing plants

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