Hall Effect Sensor

A Visual Representation

2

From Non-Destructive Testing (NDT) Resource Center

Richard Beck - Physics 141A, 2013

Hall EffectEdwin H. Hall (1879)

Definition

• Hall Effect Sensor is a Transducer

• That varies its output voltage

• In response to a magnetic field

• These are devices whose output signal

is the function of magnetic field density around it

Working of HES

Principles

• Mobile charges pressed to one side from Lorentz force, immobile charges unaltered

• Creates internal electric potential, known as Hall voltage.

• For simple metals, is V =

6

Note: t refers to the thickness of the metal along the direction of the B-field

VH =RHBI/t

t - thickness of the metal along the

direction of the B-field

Types of HESensors

• Linear(Analog) Output HES

• Digital Output HES

– Bipolar

– Unipolar

Graph – Linear Output HES

Analog output HESensor

• Hall voltage proportional to Magnetic field density

• Output can be quite small, microvolt when subjected to strong magnetic field

• Built-in amplifiers, Logic switching circuit, Regulators to improve sensitivity, hysteresis, output voltage

Digital Hall Effect Sensor

• Generally HE Switch designed to be in ‘OFF’ position (Open Circuit) when no magnetic field present

• They only turn ON (Closed circuit) when subjected to a magnetic field of sufficient strength and polarity

A Typical use: Honeywell’s magnetic position Sensor:

• “Position sensors are used in applications that require accurate, reliable outputs. They are found in brushless DC motors, utility meters, welding equipment, vending machines, home appliances, computers, and so on.”

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 with the 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)

Benefits

• 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

Digital Output HES

• When the magnetic flux passing through the HES exceeds a preset value, the output from the device switches quickly between its OFF condition to ON condition without any type of contact bounce.

• Bipolar Hall effect sensor

– Requires positive magnetic field (south pole) to operate them and negative magnetic field (north pole) to release them

• Unipolar Hall effect sensor

– Requires only a single south pole to both operate and release them as they move in and out of the magnetic field

Electric Motor ControlSome types of brushless DC electric motors use Hall effect sensors to detect the position of the rotor and feed that information to the motor controller. This allows for more precise motor control.

Current Sensor• When electrons flow through a

conductor, a magnetic field is produced.

• Thus, it is possible to create a non-contacting current sensor. This has several advantages:1. No additional resistance (a

shunt) need be inserted in the primary circuit.

2. Also, the voltage present on the line to be sensed is not transmitted to the sensor, which enhances the safety of measuring equipment. Hall effect current sensor with

internal integrated circuit amplifier.

Hall Effect Based Speed sensor

Magnetometer

• Smart phones like iPhone 3GS are equipped with magnetic compass.

• These compass measure Earth‘s magnetic field using 3-axis magnetometer.

• These magnetometer are sensors based on Hall Effect.

• These sensors produce a voltage proportional to the applied magnetic field and also sense polarity.