Proximity sensors are non – contact type sensor.
Types of Proximity Sensor:
Eddy current proximity sensor
Inductive proximity sensor
Pneumatic proximity sensor
EDDY CURRENT PROXIMITY SENSOR:
When a coil is supplied with alternating current, an alternating magnetic field is produced which
induces an EMF on it. If there is a metal near to this alternating magnetic field, on EMF is induced in it.
The EMF cause current to flow. This current flow is eddy current.
CONSTRUCTION & WORKING:
It has two identical coils.
One reference coil & another sensing coil which senses the magnetic current in the object. Eddy current start to flow due to AC(conducting object) close to sensor
Eddy current produce a magnetic field to oppose the magnetic field generated by sensing coil. Due to this opposition reduction flux is created. To detect 0.001mm
INDUCTIVE PROXIMITY SENSORS:
It consists of coil wound round a core.
Metal is close to coil Inductance changes occurs.
It is suitable for ferrous metals
PNEUMATIC PROXIMITY SWITCHES:
It is suitable for sensing non conducting materials
Air is allowed to escape from the front side of the sensor.
When there is no object air escapes freely.
When there is an object, the escaping air is blocked and return backed to system.
It is used to measure the range 3mm to 12mm
It is used in robotics for sensing elements
It is also used in NC machines, material handling systems and assembly lines. Micro switch
Photo sensitive switch Mechanical switch
It is limit switch operated by levers, rollers & cams
It is switch which requires physical contact and small force to close the contacts. Example a belt conveyor.
It is a non – contact proximity switch that consists of two magnetic switch contacts enclosed in a glass tube fined with an inert gas.
When magnet is closed switch is operated. Used for high speed applications.
Photo Sensitive Devices:
It is used to sense opaque object.
Photo detector receives a beam of light produced by the LED.
Object is passed the beam gets broken or reflected when is detected.