This is useful if you want some applications of Hall's Effect.

1. Engineering Physics Application of
Hall’s Effect in
Mechanical
Engineering
Department of Mechanical Engineering
UNIVERSITY OF ENGINEERING AND TECHNOLOGY,
LAHORE

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Figure 1: Analog
ABS Hall Sensor
Figure 2: Digital ABS
Hall Sensor
1. Anti-Lock Braking System (ABS)
 Description:
The main function of the ABS systemis to control the speed of the
wheels when the brakepedal is pressed by checking whether any of the
wheels decreases its speed faster than the others. This means that
there’s a possibility of a wheel "block". The modern equivalent is now
called "Stability Control" and is much more advanced than the standard
ABS. New cars are fitted with anti-skidsystem, which basically works
opposite to the ABS. If there is someincrease to the individual rate of
any of the wheels when accelerating, this wheel receives breaking
pressureto reduce the difference. During this time, the electronic
control unit changes the torque. The ABS indicator light does not flash
before, during and after the aboveaction, i.e. controlunit does not
perceive the situation as an error, but as the normaloperation of ABS.
 Types:
ABS sensors aredivided into twotypes:
 Passive(analog)
 Active (digital)
 Appearance:
An analog and digital ABS sensor is shown below in Fig.1 and Fig.2:

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 Principle of operation of the ABS:
ABS Sensor consists of three mainelements:
• Wheel speed sensors
• Electronic control unit (ECU) (i.e. ABS controller).
• Actuator – hydro-pneumatic unit.
Each controlled wheel is fitted with pinion and inductive sensor
comprising a permanent magnet and a coil. Rotation of the pinion
induces AC voltage in the coil sensor, which frequency is proportionalto
the angular speed and the number of teeth of the wheel.
Hydro-pneumatic unit incorporates hydraulic accumulator, electro-
hydraulic pump and valves. Individually adjustablevalves arefitted
in pair at each wheel: normally open input valve and normally closed
output valve. By controlling these valves, the ECU increases, decreases
or maintains constant pressurein the brakechamber. In the initial state
of the hydro-pneumatic unit, the two electromagnetic valves and the
hydraulic pump motor are empty. Brake chamber is connected to the
master cylinder through the open output valveand the input valveis
closed.
At normaloperating pressures (no wheel“block”) brakefluid passes
fromthe master cylinder to the brake chamber without restriction as
the pressureof the fluid in the cylinder and the chamber is equal and
proportionalto the amount of pressureapplied on the brake pedal. In
this case ABS sensor does not affect the brakesystem. During an
emergency brake (possibility of wheel “block”) the ECU controls the
electromagnets of two valves simultaneously causing them to operate.
The input valve releases the brakechamber fromthe master cylinder
and the output valve connects it with the hydraulic accumulator, thus
reducing the pressure. Simultaneously, the ECU turns on the hydraulic
pump motor to return liquid from the hydraulic accumulator in the
master cylinder. Brakechamber pressurecontinues to decrease. When
the possibility of wheel lock disappears, theECU closes the output

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Figure 3: ABS Sensor Fitted in a
vehicle
valve. The brakechamber is disconnected fromthe master cylinder and
fromthe hydraulic accumulator, and the pressurein the chamber
remains constant and less than the master cylinder. When the wheel
speed increases, the ECU turns off the input valve which opens and the
brakechamber is connected to the master cylinder again. The pressure
in the chamber increases and equalizes to the pressurein the master
cylinder. This completes one cycle of operation of ABS.
If the wheel tries to block again, next cycle is being started. System
frequency is 5Hz - 10Hz.
When ABS operates the averagepressurein the brake chamber does
not depend on the applied pressureto the brakepedal. It is determined
by the ECU and depends on the conditionof road surface.
In its full configuration ABS includes four sensors and four pairs of
valves, which allows individual control of each wheel to achieve
maximum effect and allows keeping the diagonal distribution of brake
actuators. Such systems areused to be called four-channel systems.
2. Liquid Level Sensor
 Description:

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Every car, truck and motorcycle are equipped with a
fuel level sensor to measure the amount of gasoline left in the fuel tank.
Although these sensors havebeen in place for a long time already, there
are still someevolutions ongoing and require manufacturers to consider
new solutions in order to save space, weight and costor to increase the
reliability of thesesensors and the fuel tanks. Among other, these
requirements have led to more complex tank geometries and a reduction
of the tank openings to reducefuel leakage and permeation.
 WorkingPrinciple with Appearance:
The Hall sensor is used in some automotive fuel-levelindicators. In a
vertical float system, a permanentmagnet is mounted on the surfaceof
a floating object. The current-carrying conductor is fixed on the top of
the tank, lining up with the magnet. When the level of fuel rises, an
increasing magnetic field is applied on the current, resulting in higher
Hall voltage. As the fuel level decreases, the Hall voltage also decreases.
The fuel level is indicated and displayed by proper signal condition of
Hall voltage. Another possibleimplementation of fuellevel sensor uses
a vertically moving float. Depending on whether a continuous signalor
only discretelevels are needed, solutions with magnetic sensors can be
designed based on either linear Hall sensors or Hall switches. Figure4
shows a possibleimplementation using an array of linear Hall sensors,
utilizing two small magnets that are magnetized in opposite directions.
By choosing the distance and size of the magnets properly, the
horizontalfield component turns out to be linear over a considerable
range as can be seen in Figure 5. The distance between the linear Hall
sensors then needs to be chosen in such a way that there is always at
least one sensor in its linear range. Fromthe outputs of the sensors, itis
possibleto decide which sensor output is to be taken.

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Figure 4: Vertical float based liquid level sensors using linear Hall sensors and
Hall effect switches.
Figure 5: Possible output signals from an
array of linear Hall sensors.
3. Proximity Sensors:
 Description:
Hall effect proximity sensors areused to detect
the proximity, presenceor absence of a magnetic object using a critical
distance. They function via an electrical potential that is developed across
an axis transverse to an appliedcurrent flow in the presenceof
a magnetic field.
 WorkingPrinciple:

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Figure 6-7: Proximity Sensors
There are two concepts for developing a
proximity sensor thatcan be used for accurate positioning. In the first
example, Figure6, four digital output unipolar sensors arethreaded into an
aluminum housing and actuated individually by four magnetic actuators. In
use, event signals are generated by the sensors which representdistances
measured froma reference surface. These signals define the acceptable
dimensional limits between which the item under test mustgenerate
electrical pulses. In a known application, each of the sensors has
accumulated at least 8 million operate/release cycles per month and is still
operating, without replacement or maintenance.
In the second example, Figure 7, four digital output bipolar sensors are
actuated by one magnet mounted on a rod. Applications using this concept
can achieve linear positioning accuracy of .002”. Sensing various lens
locations for photo-processing equipmentis an ideal application for this
concept. Itcould also be used to sensethe precise location of a moving
table for a 35mm slide mounter.
4. Flow Rate Sensor:
 Description:
Flow Rate Sensor is a device which is used to
measure flowrate of a liquid analog or digitally using Hall Effect Sensor.

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Figure 8: Flow Rate
Sensor
 WorkingPrinciple:
Figure8 illustrates a concept that uses a
digital output bipolar sensor and magnets mounted to an impeller to
measureflow rate for a water softener. In this design, the softener can be
made to automatically rechargeon demand, instead of on a timed basis.
Demand is determined by measuring the amount of water that has passed
through the softener. When a certain level is reached, the recharge cycle
begins. There are various methods for designing Hall effect flowmeters,
but the general principle is the same: each actuation of the sensor, by a
magnet or by shunting the magnetic field, corresponds to a measured
quantity of water. In the example shown, the magnetic field is produced by
magnets mounted on the impeller blade. Theimpeller blade is turned by
the water flow. The sensor produces two outputs per revolution. Besides
the immediate savings derived by the proper usageof the salt, this
approach provides morereliability, and longer life and the assuranceof a
continuing supply of softened water.
 Appearance:

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5. Crankshaft Position or Speed
Sensor:
The Hall Effect (named for its discoverer) utilizes the fact that a magnetic
field generates a voltagewithin a hall element. Its level is independent of its
rate of change. The sensors includethe necessary magnet (M) and the dual
hall element (DH). With the profile passing by, the magnetic field varies,
thereby creating the signal voltage within the hall element. Here it is
important to keep in mind that the signal does not fade at low speed. The
principle engages a twin chip hall element and the signal amplifier (A) uses
only the difference between both. It is then amplified to providethe power
square wave output.
A temperature compensated -40°C to+150°C (-40°F to
302°F) vaneoperated sensor is mounted in the damper
hub lip. The frequency of the output signal will be
proportionalto the speed of the crankshaft, even down
to zero speed. Since the magnetic field is being
interrupted, vibration, eccentricity and end play
tolerance have little effect on the output signal. Notches
in the lip can be used as timing marks to indicate the
position of the crankshaft. Directinterfacing of the
sensor to the on-board microprocessor adds additional
reliability to the system.
6. Conclusion:
Hence, Hall Sensors are widely used not only in Mechanical Engineering
field but also in the latest technologies. They havefound vastapplications
in Automotive industries too.
Figure 9: Crankshaft
Speed Sensor