How to read electrical relay diagram? [Standard symbols used for drawing electrical relay diagram]

In one of the previous post in instrumentpedia I have described how to read an electrical drawing. Now lets look what is electrical relay diagram. Here I am giving the standard symbols used for the electrical relay diagram. In earlier days instead of PLC or DCS like controllers relays are used as controllers. Nowadays also for controlling small systems relays are using as controllers. Comparing to other controllers it is very cheap. Electrical control circuits are drawn with the standard symbols which are given below.

Components used for making a electrical control circuit and its standard symbols.

Switches.
Selectors.
Push buttons.
Contacts.
Coils.
Motors.
Pilot lights.
Alarms.
Connections