CHAPTER 4 : RELAY

Actuator is any devices that converts an electrical signal into mechanical motion. So, actuator like as output. One type of relay is relays. Relay is simple electromechanical switch made up of an electromagnet and a set of contacts. Another explanation is an electrically operated device that mechanically switches electric circuit.

1. There are four components in relay: electromagnetic, armature, spring, set of electrical contacts. Relay has control over several variables:The voltage and current that is needed to activate the armature
2. The maximum voltage and current that can run through the armature and the armature contacts
3. The number of armatures (generally one or two)
4. The number of contacts for the armature (generally one or two -- the relay shown here has two, one of which is unused)
5. Whether the contact (if only one contact is provided) is normally open (NO) or normally closed (NC)

From the figure above, we can analyze that if button we push number 87a is known as Normally Closed (NC) because it isNormally closed.That means it lets current flow through it in its normal statea and number 87 is known as Normally Open (NO) because (you guessed it) it's Normally open. That means it wont let current through in its normal state.

References :

Petruzella, D. Frank (1996). Industrial Electronics. New York : McGraw-Hill

http://electronics.howstuffworks.com/relay1.htm

http://www.allcorsa.co.uk/forums/showthread.php/relays-work-42660.html