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Relays as switching devices

Problem: The signal output of a small reed is too weak to switch a DC-motor. Solution: Using a relay!

Relay as a swiching step

Relay as a swiching step

Functioning of a relay:

Relays are electromechanical devices consisting of an electromagnet und some contacts. The switching mechanism is carried out when the electromagnet is under voltage – that means the relay is “activated”.

Relay are mainly used when a low-power signal has to control a circuit with high power.

Relay - function, Relay - how it works

Relay - function

Advantages of a relay compared with electronic switches:

  • Galvanic isolation (if you don´t use an opto-coupler)
  • Higher switching capacity


  • Low switching frequency
  • Mechanical switching means wearing

Relay for memory functions within the control circuit

Problem: The memory function of the valve is lost with the spring reset.

Solution: The memory function must now be carried on the control side, i.e. the electrical circuit. The solution is a so-called latching relay:

Latching relay circuit - how it works

Latching relay circuit - how it works