Relay
is one of the most important electromechanical devices highly used in
industrial applications specifically in automation. A relay is used for
electronic to electrical interfacing i.e. it is used to switch on or off
electrical circuits operating at high AC voltage using a low DC control
voltage. A relay generally has two parts, a coil which operates at the
rated DC voltage and a mechanically movable switch. The electronic and
electrical circuits
are electrically isolated but magnetically connected to each other,
hence any fault on either side does not affects the other side.
Relay switch
shown in the image above consists of five terminals. Two terminals are
used to give the input DC voltage also known as the operating voltage of
the relay. Relays
are available in different operating voltages like 6V, 12V, 24V etc.
The rest of the three terminals are used to connect the high voltage AC
circuit. The terminals are called Common, Normally Open (NO) and
Normally Closed (NC). Relays are available in various types &
categories and in order to identify the correct configuration of the
output terminals, it is best to see the data sheet or manual. You can
also identify the terminals using a multimeter and at times it is
printed on the relay itself.
The internal structure of the relay is shown in the image above which is embedded inside the plastic covering.
The above image shows the DC coil used to create the necessary electromagnetic force when current is passed through the wires.
The
above image shows the spring that keeps the lever in contact with the
NC terminal when there is no current flowing in the coil.
Please identify that which terminal is normally open and which is normally close. I am not able to understand with diagram only. Some lecture will also be helpful.
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