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TRANSDUCERS

Presentation

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Hall Effect

The effect of generating a measurable voltage

by using a magnetic field is called the Hall

Effect after Edwin Hall (1879)

In its most common application, a Hall

effect transducer serves to measure a

magnetic field and convert that

measurement into voltage

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Hall Voltage

Working Principle: If a strip of conducting

material carries a current in the presence

of a transverse magnetic field, a potential

difference is produced between theopposite edges of the conductor.

The output Hall voltage is given as:

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Hall Effect Transducers

Hall Effect Sensors consist of a thin piece ofrectangular p-type semiconductor material

such as Ga-As, In As passing a continuous

current through itself. When the device is

placed within a magnetic field, the magnetic

flux lines exert a force on the semiconductor

material which deflects the charge carriers,

electrons and holes, to either side of thesemiconductor slab

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Hall Effect Transducers

To ensure maximum sensitivity themagnetic lines of flux must always be

perpendicular to the sensing area of

the device and must be of the correctpolarity

To ensure linearity, high field strength

magnets are required that produce alarge change in field strength for the

required movement.

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Applications of Hall Effect

Transducers

Magnetic to Electrical Transducer

Measurement of displacement

Measurement of current

Measurement of power

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Typical Applications

Switched Mode Power Supplies Uninterruptible Power Supplies (UPS)

Over voltage protection

Feedback of control systems Electric power network monitoring

AC frequency conversion servo-

motors Various power supplies

Power supply for welding applications

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Ways of Detecting a magnetic

field Head-on Detection:

It requires that themagnetic field isperpendicular to thesensing device and that it

approaches it straight ontowards the active face.This head-on approachgenerates an output signal,VH which in the lineardevices represents the

strength of the magneticfield, the magnetic fluxdensity, as a function ofdistance away from thesensor.

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Ways of Detecting a magnetic

field Sideways Detection:

This requires movingthe magnet across theface of the Hallelement in a sideways

motion. Sideways orslide-by detection isuseful for detecting thepresence of amagnetic field as itmoves across the faceof the Hall elementwithin a fixed air gapdistance for example,counting rotationalmagnets or the speed

of rotation.

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Digital Transducers

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Contents

Shaft Encoders

Incremental Optical Encoder

Absolute Optical Encoder

Encoder Error

Digital Resolvers

Digital Tachometers

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INTRODUCTION

What is a Digital Transducer ? Any transducer that presents information as discrete

samples and that does not introduce a quantization errorwhen the reading is represented in the digital form may beclassified as a digital transducer

What is an encoder ? Any transducer that generates a coded of a measurement

can be termed an encoder

SHAFT ENCODERS

They are Digital Transducersthat are used for measuring ANGULARDISPLACEMENTS and ANGULAR VELOCITIES.

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Applications Of Shaft Encoders

1.) Control of robotics manipulators2.) Machine tools

3.) Digital tape-transport mechanisms

4.) Servo plotters

5.) Printers

6.) Satellite mirror positioning system

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Encoder Types

Shaft encoders can be classified into threecategories

1. Incremental Encoders

2. Incremental Optical Encoders3. Absolute Optical Encoders

Incremental Encoders

1.Optical (photo sensor) method2.Sliding contact (Electrical conducting) method

3.Magnetic saturation (Reluctance) method

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Optical Encoder

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Optical Encoder

The optical encoder uses an opaque disk that hasone or more circular tracks, with somearrangement of identical transparent windows.

A parallel beam of light is projected to all tracks

from one side of the disk The light sensor could be a silicon photodiode, a

phototransistor, or a photovoltaic cell.

The light from the source is interrupted by theopaque areas of the track, the output signal fromthe probe is a series of voltage pulses

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Incremental Optical Encoders

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Incremental Optical Encoder

The disk has a single circular track with

identical and equally spaced transparent

windows.

The area of the opaque region between

adjacent windows is equal to the window

area.

Two photodiode sensors (pick offs 1 and

2) are positioned facing the track a

quarter-pitch

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Absolute Optical Encoders

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Absolute Optical Encoders

The disk has a circular track withidentical and equally spaced transparent

windows.

In absolute optical encoders photo sensorsare not used.

The output can be binary, gray code,

natural binary code.

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Encoder Error

Any transducer that generates a coded readingof a measurement is known as Encoder.

The primary sources of errors in shaft

encoder are:1) Quantization error

2) Assembly error

3) Coupling error

4) Structural limitations

5) Manufacturing tolerances

6) Ambient effects

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Digital Resolvers

Digital resolvers or mutual induction encodersoperate using the principle of mutual induction.

They are commercially known as Inductosyns

A digital resolver has two disks namely statorand rotor which is coupled to the rotating object.

The rotor has fine electric conductor foilimprinted which is connected to a highfrequency AC supply.

The stator has two separate printed patternsidentical to the rotor pattern but are shifted by aquarter-pitch from one another

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Digital Tachometers

As Shaft encoders are also used for measuring angularvelocities, they can be considered as Tachometers.

A Magnetic induction tachometer of variable-reluctance

type is shown in figure.

Teeth on the wheel are made of ferromagnetic material.

Two magnetic induction proximity probes are placed

facing the teeth radially, a quarterpitch apart.

Speed is computed either by counting pulses over asampling period or by timing the pulse width.