Electromagnetic Relays are mechanical switches which use magnetic fields to move the switch position. Current is run through a coil to create the magnetic field.
- Active High (module). High signals moves the switch from NC to NO and holds it there as long as the signal is applied.
- Active Low (module). Low signal moves the switch from NC to NO and holds it there as long as the low signal is applied.
- Bistable/Latching. a pulse moves the switch
Since relays depends on an inductive coil, it is advised to use a (flyback) diode parallel to the coil. The diode is reverse biased in relationship to the power supply, which gives a safe current path for the inductive kickback of the coil when power is cut.