Position Sensor Optical Encoders

POSITION SENSOR 

OPTICAL ENCODERS

It is used to measure position, velocity, acceleration and direction of movement of rotors.

INCREMENTAL ENCODERS

PRINCIPLE:

When a beam of light passes through slots in a disc, it is sensed by the light sensor opposite to the light source

When the disk is rotated, a pulsed output is produced by sensor with number of pulsesbeing proportional to the position of the disc and number of pulses per second

determines the velocity of the disk

CONSTRUCTION & WORKING:

It consists three components light source, coded disk and photo detector

The disk is made up of plastic or glass.

The disk consists of opaque and transparent segment alternatively.

The wheel is between light and photo detector.

The photo detector receives the light signal alternatively which is converted into electrical signal.

ABSOLUTE ENCODERS

PRINCIPLE:

The principle of operation is that they provide a unique output corresponds to each rotational position of the shaft.

The output is in the form of binary numbers representing the angular position.

CONSTRUCTION & WORKING:

The disc has four concentric slots and four photo detectors to detect the light pulse.

The slots are arranged in such way that they give a binary number.

It consist opaque and transparent segments. This pattern is called as track.

The encoders have 8 to 14 slots.

The number of the track determines the resolution of the encoder.

The number of bits in binary number will be equal to the number of tracks.

HALL EFFECT SENSORS:

Principle:

When a current carrying semiconductor plate is placed in a transverse magnetic field, it experiences a force (Lorentz force). Due to this action a beam of charged particles are

forced to get displaced from its straight path. This is known as Hall Effect.

A current flowing in a semiconductor plate is like a beam of moving charged particles and thus can be deflected by a magnetic field. The side towards which the moving

electron deflected becomes negatively charged and the other side of the plate becomes positively

charged or the electrons moving away from it.

This charge separation produces an electrical voltage which continues until the Lorentz force on the charged particles from the electric field balances the forces produced by the

magnetic field. The result is a traverse potential difference known as Hall voltage.

Construction & Working:

Current is passed through leads 1 and 2 of the semiconductor plate and the output leads are connected to the element faces 3 and 4.

These output faces are at same potential when there is no transverse magnetic field passing through the element and voltage known as Hall voltage appears when a

transverse magnetic field is passing through the element.

This voltage is proportional to the current and the magnetic field.

The direction of deflection depends on the direction of applied current and the direction of magnetic field