Relays

Relay Functions

The most important distinguishing features between different relays are the following: type of control (monostable or bistable), contact function (switching or closing) and number of poles (1 or 2 are by far the most common.

Monostable relay – continuous control: When the control signal to the relay coil is removed, the relay contact returns to its rest position (normal state) with the help of a return spring. This is the most common relay type.

Bistable / latching relay – pulse control: The relay contact maintains its contact position after the control signal to the coil is removed. No return spring is present. A short pulse is enough to switch the contact position.

Switching contact: The relay contact has three terminals – common (COM), normally open (NO), and normally closed (NC). The function corresponds to an on-on switch.

Closing contact: The relay has two terminals and is normally open (NO). The contact closes when the relay coil is energized. The function corresponds to an on-off switch.

Relay Poles: A relay can have one or more poles. The number of poles indicates how many separate circuits can be controlled independently. Example: A 2-pole switching relay has two separate contacts, each with three terminals (COM, NO, NC). This results in a total of 2 × 3 = 6 contact terminals. In addition, there are 2 terminals for the relay coil. In total, the relay has 8 pins/connections.