The Hall Effect SensorThe Hall Effect Sensor

Rene DupuisRene Dupuis

Background InformationBackground Information

The Hall effect was discovered by Edwin Hall The Hall effect was discovered by Edwin Hall in 1879; “electron” was not experimentally in 1879; “electron” was not experimentally discovered; had to wait until quantum discovered; had to wait until quantum mechanics came mechanics came Development of semiconductor compoundsDevelopment of semiconductor compoundsin 1950's led to first useful Hall effect magneticin 1950's led to first useful Hall effect magneticinstrumentinstrumentIn the 1960's, first combinations of Hall In the 1960's, first combinations of Hall elements and integrated amplifiers elements and integrated amplifiers

Resulted to classic digital output Hall switchResulted to classic digital output Hall switch In 1965, first low-cost solid state sensorIn 1965, first low-cost solid state sensor

Theory of the “Hall Effect”Theory of the “Hall Effect”Hall effect principle, no magnetic field

Hall effect principle, magnetic field present

Potential Difference (voltage) across output:

V = I * B

Basic Hall Effect SensorBasic Hall Effect Sensor

Hall elementHall element is the basic magnetic field sensor

Differential AmplifierDifferential Amplifier

amplifies the potential difference (Hall voltage)

RegulatorRegulator holds current value so that the output of the sensor only reflects the intensity of the magnetic field

BOP — Operate pointBOP — Operate point A positive magnetic A positive magnetic

field > BOP will switch field > BOP will switch the sensor on (output the sensor on (output low). low).

BRP — Release pointBRP — Release point Removal of the Removal of the

magnetic field < BRP magnetic field < BRP will switch the sensor will switch the sensor off (output high). off (output high).

Bhys — HysteresisBhys — Hysteresis

UnipolarUnipolar

LatchingLatching

BipolarBipolar

Types Magnetic Parameters

UnipolarUnipolar

Requires single polarity magnetic field for operation

Positive magnetic field (South pole)

Directed towards branded face of the sensor for activation

True-Power-On State <BOP or >BRP

LatchingLatching

Require both positive and negative magnetic fields

Symmetrical Duty Cycle operation

Guaranteed power-up state

>BOP or <BRP

BipolarBipolarInvolves either Unipolar or Involves either Unipolar or Latching characteristicsLatching characteristics

Same principleSame principle

Unipolar Mode

Latching Mode

Sensor switch operation

Power-up states

Hall Effect Sensor ExampleHall Effect Sensor Example

Application: Response to South or North Polarity

Motor-Tachometer application where each rotation of the motor shaft is to be detected

When ring magnet rotates w/ motor, South Pole passes the sensing face of the Hall sensor after each revolution.

Sensor Actuated when the South Pole

approaches sensor Deactuated when South Pole

moves away from sensor

Single digital pulse produced for each revolution.

Application: Gear Tooth Sensing

• Sensor detects change in flux level • Translates it into a change in the sensor output (high to low)

• Sense movement of ferrous metal targets (magnetically biased)

BenefitsBenefits

Small and rugged non-contact sensors

Insensitive to oil, dirt, humidity and dust

High magnetic sensitivity Accurate and Reliable

Delivers low Power consumption

Supply voltage capability

Average current consumption

Prices and SourcesPrices and Sources

Range from $1-$60Range from $1-$60

Allied ElectronicsAllied Electronics

Allegromicro Allegromicro

Digi-KeyDigi-Key

SensorSensor IndicateIndicatessDirectioDirectionn

OutputOutput RotationalRotationalor Linearor Linear

NotesNotes

Optical Incremental Encoders

YesYes Digital Digital

(Quadrature)(Quadrature) BothBoth Uses light and Uses light and

optics to sense optics to sense motionmotion

Interrupters NoNo Digital Digital

(Single Pulse)(Single Pulse) RotationalRotational Senses light Senses light

with light beam with light beam interruptinterrupt

Photo-reflective sensors

NoNo Digital Digital

(Single Pulse)(Single Pulse)

LinearLinear Generates Generates pulse whenever pulse whenever sensor receives sensor receives reflected light reflected light

Laser Interferometer

Yes Yes Digital Digital (Quadrature)(Quadrature)

LinearLinear Laser supply Laser supply linear linear displacement of displacement of an objectan object

Triangulation Sensors

YesYes AnalogAnalog LinearLinear Laser supply Laser supply non-contact non-contact linear linear displacement of displacement of an objectan object

Hall-Effect Hall-Effect SensorsSensors

NoNo Digital Digital (Single Pulse)(Single Pulse)

RotationalRotational

QUESTIONS?QUESTIONS?