Switch Image

Switches

1. Switches are used to open or close a circuit.

2. The on position is also called make or closed position. The off position is also called break or open position.

3. In on position, the switch has very little resistance and  zero voltage drop across it.

4. Open switch has infinite resistance and no current flows in the circuit. But in an open position, the applied voltage is across the switch contacts. Therefore, the insulation must be good enough.


TYPES OF SWITCHES

(1) Toggle switches

(2) Microswitches keyboard switches

(3) push button switches

(4) rotary band-change switch

(5) thumbwheel switch

(6) proximity switches

(7) knife switches

(8) lever switches

(9) crossbar switches.


1. Toggle switches

a) These switches are used for On/Off control of ac mains or dc power supplies.

b) Single, double and many poles and single or double throw toggle switches are used in electronic instruments, computers and domestic On/Off operations.

c) SPST (Single-pole single-throw) Switch provides an on or off position for one circuit. Two connections are necessary.

d) SPDT (single-pole double throw) switch can control two circuits.

e) DPST (double-pole single-throw) switch has only one position of closure but two contacts simultaneously f) Both sides of a two wire line are switched at the same time.

g) DPDT (double pole double-throw) switch requires six connections. It can be used to connect a TV receiver to antenna or cable TV connection.


2. Micro Switches 

a) These switches are of snap action type, operated by pressure.

b) They are used as limit switches, control or safety switches in electronic equipment.


3. Push button switches

a) Single on-off push buttons are similar to toggle switches.

b) Multiple contact push button switches are known as slider switches.


4. Rotary band-change switches 

The multiple pole, multiple way rotary switches are used in radio receivers, measuring instruments etc.


5. Thumb wheel switch

a) Single or multiple pole, decimal or binary coded switches are used in computer or measuring instruments.

b) Thumb wheel adjustment with 10 positions is available.


6. Proximity switches 

a) These switches are used in industry, plain paper copiers, lifts etc.

b) These work on photo operated or electromagnetic

circuits.


7. Knife switches 

a) These are used in power switch boards.

b) Maximum  current that can be carried by them is upto 300 A at 500 v.


8. Lever switches 

a) These consist of an insulated rocker arm operating contact.

b) Locking and unlocking arrangements are available.