What is Push Button Switch?
Push Button Switch is a pilot device which provides control of an equipment by pressing an actuator which looks like a button Push button switch can be divided into two parts One part is the mechanical actuator or button assembly and the second part is the electrical portion or contact assembly called the contact block.
The mechanical actuator or button assembly can be of momentary contact spring returned type or of maintained contact type The momentary contacts spring returned push button remains actuated as long as the button is physically held pressed by the human operator.
Under pressed condition the contacts change their positions in the contact block Once the button is released the contacts return to their normal position.
Maintained contact push buttons are held actuated by some latching mechanism even when the operator releases the pressure on the push button.
Such units consist of two push buttons, only one remains in actuated position at a time, when the other button is pressed the first one gets released.
A spring returned momentary contact push button is shown in Fig.
The contact block has two contacts, one normally open ( and the other normally closed (When the push button is pressed, NC contacts opens and NO contact closes.
When the push button is released a spring inside the actuator assembly brings back the push button and a spring inside the contact block brings the contacts back to their normal position.
The symbol for the push button switch is also shown in Fig.
Types of Push button switches
Push button switches can be of different types depending upon the type of actuator assembly
They are:
Recessed button type
Mushroom head type
Illuminated type
Key lock type.
Colour of the button is also an important factor in push button switches Standards have been developed which specify certain colour for a particular function.
For example, red push buttons are used for stop and emergency stop operations, while green push buttons are used for start operations.
When two or three push button switches are mounted on a steel or plastic enclosure it is known as a push button station. For example, in a three push button station, one push button may be for running the motor in forward direction, the second for running the motor in reverse direction, and the third for stopping the motor.
