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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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Types of Magnetic Sensors
Magnetoresistive Sensor
Magnetostrictive Sensor
Hall Effect Sensor
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Magnetoresistive Sensor
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Magnetoresistive Sensor
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
Magnetoresistive Sensor
MEMSIC's
AMR Sensor
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Types of Magnetic Sensors
Magnetoresistive Sensor
Magnetostrictive Sensor
Hall Effect Sensor
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Magnetostrictive Sensor
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Types of Magnetic Sensors
Magnetoresistive Sensor
Magnetostrictive Sensor
Hall Effect Sensor
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Linear Amplifier
Assume Vout- of the Hall device is tied to ground
Goal: Amplify Hall Voltage
=5 V
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Schmitt Trigger
Design with Two Transistors
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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
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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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik
Hall Effect Sensor IC
Honeywell SS49E Optek OHS180U
(Unipolar)
Optek OHS3175U
(Bipolar)
Melexis MLX90217
Optek OHS185U and OHS3175U Melexis MLX90217
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