Tuesday 10 November 2015
Monday 2 November 2015
Working of Relays
What is a relay?
We know that most of the high end industrial application
devices have relays for their effective working. Relays are simple switches
which are operated both electrically and mechanically. Relays consist of a n
electromagnet and also a set of contacts. The switching mechanism is carried
out with the help of the electromagnet. There are also other operating
principles for its working. But they differ according to their applications.
Most of the devices have the application of relays.
Why is a relay used?
The main operation of a relay comes in places where only a
low-power signal can be used to control a circuit. It is also used in places
where only one signal can be used to control a lot of circuits. The application
of relays started during the invention of telephones. They played an important
role in switching calls in telephone exchanges. They were also used in long
distance telegraphy. They were used to switch the signal coming from one source
to another destination. After the invention of computers they were also used to
perform Boolean and other logical operations. The high end applications of
relays require high power to be driven by electric motors and so on. Such
relays are called contactors.
Relays are also named
with designations like
·
Single Pole Single Throw (SPST) – This type of
relay has a total of four terminals. Out of these two terminals can be
connected or disconnected. The other two terminals are needed for the coil.
·
Single Pole Double Throw (SPDT) – This type of a
relay has a total of five terminals. Out f these two are the coil terminals. A
common terminal is also included which connects to either of two others.
·
Double Pole Single Throw (DPST) – This relay has
a total of six terminals. These terminals are further divided into two pairs.
Thus they can act as two SPST’s which are actuated by a single coil. Out of the
six terminals two of them are coil terminals.
·
Double Pole Double Throw (DPDT) – This is the
biggest of all. It has mainly eight relay terminals. Out of these two rows are
designed to be change over terminals. They are designed to act as two SPDT
relays which are actuated by a single coil.
Relay Applications
·
Relays are used to realize logic functions. They
play a very important role in providing safety critical logic.
·
Relays are used to provide time delay functions.
They are used to time the delay open and delay close of contacts.
·
Relays are used to control high voltage circuits
with the help of low voltage signals. Similarly they are used to control high
current circuits with the help of low current signals.
·
They are also used as protective relays. By this
function all the faults during transmission and reception can be detected and
isolated.
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