BASIC ELECTRICAL COMPONENTS

 BASIC ELECTRICAL COMPONENTS

Following are the generally encountered electrical components in electro pneumatics.

• Push buttons
• Rocker switch
• Limit switch
• Proximity switch
• Indicators

3.1 Push buttons

These are generally of three types.

• NO (Normally open) type
• NC (Normally closed) type
• Change over type

In NO type when the button is pressed the moving switching element acts against the force of the spring and closes the terminals.When the button is released the spring restores the contact to its original position

NO TYPE PUSH BUTTON SWITCH

 

In NC type when the button is pressed the moving switching element acts     against the force of the spring and opens the terminals.When the button is

released the sping restores the contact to its original position

NC TYPE PUSH BUTTON SWITCH

     

In Change over type when the button is pressed the NC contacts are separated and interrupt the circuit .The switching element closes another set of  NO contacts thus closing the circuit. When the button is released the spring restores the switching element to their original position  

 

CHANGE OVER TYPE PUSH BUTTON SWITCH

3.2 Rocker switch

Latching type switches are also called rocker switch that is after actuating the switch the contacts are mechanically latched. Pressing the rocker again releases the latch and switch returns to its original state.

 

 

ROCKER SWITCH

3.3 Limit switch

These are used to indicate particular end positions of the motions of cylinders or machine parts .The significant points to consider when selecting such a signal input element are the mechanical stress, contact reliability and precision of the switching point .  

LIMIT SWITCH

3.4 Proximity switches

It is an important component in an automated control systems.It transmits information relating to the operating conditions of a machine to the logic processing system. The different types of proximity switches are as below

• Inductive proximity sensor.
• Capacitive proximity sensor
• Photo electric sensor

Inductive proximity sensor: This essentially comprises an oscillator whose windings constitute the sensing face. An alternating magnetic field is generated in front of these windings

INDUCTIVE PROXIMITY SWITCH

Capacitive proximity sensor: This comprises an oscillator whose capacitors constitute the sensing face. When a conducting or insulating material  is placed within this field it modifies coupling capacitance and starts the oscillation.

CAPACITIVE PROXIMITY SENSOR

Photo electric type:

A photo electric sensor will give a switching signal when a present level of light is received. These are used to detect the presence of moving objects. The switch signal produced by the moving object can be fed into the electrical control circuit to provide a corrective motion. The three common arrangements for photo electric sensing are

• Reflective type
• Retro reflective type
• Separate type

PHOTO ELECTRIC PROXIMITY SENSOR

Retro reflective type

Retro reflective type

 

 

Separate type

Separate type

 Sensing distance of photo electric sensors depends on

• Type and material of the sensing object
• Sensing head size of the sensor

Advantages of these sensors are

• High switching frequency
• No contact bounce
• No moving part
• Immune to the effects of shock and vibration

 

3.5 Indicators

These are electrical signal output devices.Indicators used in electro pneumatic  circuits produce output in audio or optical indication. A buzzer produces sound signal when it receives electrical signal.A bulb or LED can produce light when it receives electrical signal

 

Indicators