Lecture 6 - Weber State Universityfaculty.weber.edu/snaik/ECE5900_ECE6900/06Lec06_Magnetic.pdf1 ECE...

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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik

ECE 5900/6900: Fundamentals of Sensor Design

Lecture 6Magnetic Field Sensing and Hall Effect Sensors

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Magnetic Field Sensing

Q: What are we measuring?

A: Change in magnetic field (flux and orientation) in

order to determine position and motion

SI unit: Tesla

CGS unit: Gauss

1 Tesla=10,000 Gauss

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Position and Motion Sensing with Magnetic Field

Non-contact Sensors

Honeywell SS49E Optek OHS180U

(Unipolar)

Optek OHS3175U

(Bipolar)

Melexis MLX90217

Hall Effect Sensors

Magneto-resistive Sensors

MEMSIC MMC3416xPJ Honeywell SM353LT

Magnetostrictive Sensors

MTS Temposonic GP

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Examples: Applications of Magnetic Sensors

Industrial Linear Position Sensing with Magneto-resistive and

Magnetostrictive devices

Position Feedback for Control of

Hydraulic Cylinder Position Monitoring of Motion Simulator

Position monitoring of Automated Production Equipment

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Examples: Applications of Magnetic Sensors

Pipeline Monitoring with PIG and Hall Sensors

Rotary Position Monitoring with Hall devices

Ref: http://sine.ni.com/cs/app/doc/p/id/cs-16372

Learn more about PIG: https://youtu.be/X5S48nytYJg?t=128

Measure Hard-drive

rotation speed

Optimize Throttle Response

and Electronic Ignition

Measure Speed and Position of

Gear Tooth

http://sine.ni.com/cs/app/doc/p/id/cs-16372

https://youtu.be/X5S48nytYJg?t=128

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Types of Magnetic Sensors

Magnetoresistive Sensor

Magnetostrictive Sensor

Hall Effect Sensor

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Ref: Sensor&Transducers by Y.Cai, et. al., MEMSIC Inc,

http://www.memsic.com/userfiles/files/publications/Articles/Electronic_Products_Feb_%202012_Magnetometer.pdf

Permalloy (NiFe)

(a) Change in the magnetization (alignment of magnetic domains) and

(b) Change in magnetoresistance due to an applied magnetic field

(a) (b)

1) The resistance of the Permalloy film changes as a function of the angle θ

between the vector M and a current I flowing through it.

2) Smallest resistance when θ=90°

(c)

(c) Alignment of magnetic domains

under strong magnetic field before using the film as sensor

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Ref: http://archives.sensorsmag.com/articles/0399/0399_18/main.shtml

Basic MR Sensor Circuit with Wheatstone Bridge

and Bridge Amplifier

Bridge Amplifier with feedback to remove

offset and temperature drift

Vehicle Detection using

3-axis AMR Sensor

1) The type of vehicle

(e.g., car, truck, bus)

can be classified through pattern

recognition algorithms

2) AMR sensors are also used in

smart phones and tablets as

e-compass

Anisotropic


MEMSIC's

AMR Sensor

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Hall Effect Sensor

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A current pulse is sent through the waveguide (sensing material); the magnetic moments

in the waveguide align themselves (right hand rule) and axial magnetic field is generated

A permanent magnet is mounted on movable part whose position has to be measured.

The permanent magnet causes twisting; the interaction of two magnetic fields produces a

mechanical strain pulse, which travels as the ultrasonic wave.

A pickup coil detects the ultrasonic wave and generates a voltage or current: which is

amplified (the wave in the opposite direction is dampened by damper).

The permanent magnet position is determined as function between start and stop time of

the pulse.

MTS Temposonic GP

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Hall Effect Sensor

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Hall Effect Sensor (HES)

Hall Effect Sensor is made up of P-type

semiconductor and has four electrodes.

DC voltage is applied between the left (L)

and right electrodes (R).

Free Electrons move within the electric field

through the Hall material

When magnet comes closer to the Hall plate,

the magnetic field B creates Lorentz force FB

on the electrons,

FB=-qvBsinθ; where v=velocity of electron, θ=angle between velocity vector and the

magnetic field B.

Lorentz force causes the deflection of electrons towards bottom electrode (Bo) and holes

towards the top electrode (T): charge separation

The charge separation creates the electric field and hence Hall Voltage VH.

The electric field creates the electric force FE =qE on the electrons, where q=1.6x10-19 C

to maintain equilibrium

Watch animation: https://en.wikipedia.org/wiki/Hall_effect

L RT

B

o

VEX

B

https://en.wikipedia.org/wiki/Hall_effect

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Hall Effect

; where I= DC current through the Hall device

B=applied magnetic field flux

e= electron charge=1.6x10-19 C

d= thickness of the material

n=charge carrier density of the material

ned

IBVH

VH [V]

B [Gauss]

South PoleNorth Pole

Slope=Sensitivity, SA= VH/B [mV/Gauss]

decreases as VEX decreases

SA= VH/B=I/ned (for d=250 μm, ned=40)

Usually I is in the order of 10s of μA

Q: How do you increase sensitivity?

A: 1) Increase the bias current I

2) Decrease thickness d (during fabrication)

3) Lower concentration n (by using better

electrodes or more p-type doping)

Transfer Function

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Hall Effect Sensor for Gear Tooth Position and Speed

Ref Animation

http://www.melexis.com/Assets/Hall-Effect-Geartooth-Sensor--3721.aspx

Measure1) Sproket speed

2) Chain link conveyor

speed

3) Camshaft speed

4) Also used in Tachometers,

Counters

ChenYang Technologies CYGTS104U-S

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Hall Effect Sensor for Rotary Motion: Block Diagram

Hall Device

Linear

AmplifierSchmitt

Trigger

Sensing element

Convert

periodically

applied magnetic

field flux (rotation)

into voltage (mV

range)

Amplify the Hall

voltage

Common-

Emitter NPN

Amplifier Design

Create

comparator circuit

Create digital

pulse based on the

amplified Hall

voltage

Ref Animationhttp://www.melexis.com/Assets/Hall-Effect-Geartooth-Sensor--3721.aspx

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Hall Device: Model

Ref: Hall Effects Sensors: Theory and Application by Ramsden

Rin=input resistance

Rout=output resistance

VBias=VEx

Eout=Hall voltage

Model Assumptions

[1] no saturation at high B

[2] temperature effects are

ignored

[3] no zero B offset

[4] symmetric sensor

(sense electrodes are in the

center on the sides

Goal: Convert Magnetic Rotation into Voltage

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Linear Amplifier

Assume Vout- of the Hall device is tied to ground

Goal: Amplify Hall Voltage

=5 V

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Schmitt Trigger

Design with Two Transistors

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Schmitt Trigger

Design with an Opamp (S&S: Section 17.4)

VR

VR = 0 VR ≠ 0

Learn more about Schmitt Trigger: https://youtu.be/Nrp8OgQLAlw

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Hall Effect Sensor IC

Honeywell SS49E Optek OHS180U

(Unipolar)

Optek OHS3175U

(Bipolar)

Melexis MLX90217

Optek OHS185U and OHS3175U Melexis MLX90217

Lecture 6 - Weber State Universityfaculty.weber.edu/snaik/ECE5900_ECE6900/06Lec06_Magnetic.pdf1 ECE...

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Transcript of Lecture 6 - Weber State Universityfaculty.weber.edu/snaik/ECE5900_ECE6900/06Lec06_Magnetic.pdf1 ECE...