Transcript Transducers and Sensors - Georgia Institute of Technology

ME8843
ME 6408
Advanced Mechatronics
Instructor: Professor I. Charles Ume
Hall effect Sensors
Variable Reluctance Sensor
Ultrasonic Sensors (Sonic Distance Sensors)
Photo Interrupt
Pressure Sensors
Accelerometers
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ME8843
Hall Effect Sensors
• Developed by
Edwin Hall in 1879;
and hence the
name Hall effect
Hall Effect Sensor Sensing a Shaft Speed
• Used to:
– provide noncontact
means to detect and
measure magnetic
field
http://farm1.static.flickr.com/62/227729006_fab88c1668.jpg?v=
0
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ME8843
How they work
• Presence of magnetic field
deflects electrons flowing
through conductive material
Depiction principle of the
Hall Effect
• As electrons move to one end
of conductive material:
– Potential is developed in
direction perpendicular to gross
current flow
– Potential indicates strength of
magnetic field
http://upload.wikimedia.org/wikipedia/commons/a/ab/Ha
ll_effect_A.png
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Applications
• IC Engine Electronic Ignition Systems
– Used to determine position of cam shaft
• Brushless DC Motor Control
– Sensors determine position of permanent magnet
rotor
• Assembly Lines
– To determine shaft position and velocity
– As contactless limit switches
• Current Sensing ICs
– Electrically isolated alternative to shunt resistors
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Hall Effect Sensor Types
• Linear Hall Effect Sensors
– Output is proportional to magnetic field
strength
• Hall Effect Digital Switches
– Presence of magnetic field above threshold
turns switch on
– Presence of magnetic field below threshold
turns switch off
• Hall Effect Digital Latches
– North field turns latch on
– South field turns latch off
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ME8843
Packaging and Manufacturers
• ICs
– Analog Devices:
• AD22151G from Analog Devices
SOT23
– Allegro MicroSystems, Inc.
• Wide range of linear, latching and
switching sensors
• Great sampling policy
SIP
http://www.allegromicro.com/en/Products/P
art_Numbers/1120/pinout.gif
– Many, many more
• Packaged units
– Honeywell
– Many, many more
Hall Effect
Sensor Module
http://sensing.honeywell.com/client_asset/do
cument/1/5/4/0/3/5/document_C3697B35C930-CB7C-FE090DFFCE61FB22.jpg
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Implementation and Words of Warning
• Sensors may be affected by temperature
variation.
– Some sensors incorporate circuitry to reduce this error.
• Sensors may be directional:
– Care must be taken with respect to orientations of
sensor and magnet
• Some Hall Effect sensors detect presence
of ferromagnetic materials, not magnetic
fields
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ME8843
Variable Reluctance Sensors
• Used to measure speed
and/or position of moving
metallic object
• Sense change of magnetic
reluctance (analogous to
electrical resistance) near
sensing element
• Require conditioning circuitry
to yield a useful signal (e.g.
LM1815 from National Semi.)
Industrial Variable
Reluctance Sensor
http://www.motionsensors.com/railwithoring
2.jpg
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ME8843
How Variable Reluctance Sensors Work
• Magnet in sensor creates magnetic field
• As ferrous object moves by sensor
– Resulting change in magnetic flux induces emf in
pickup coil
Variable Reluctance Sensor
Construction
Typical Configuration
http://www.instronics.com/images/sensoronix/image.ds.drawing.v
r.jpg
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Typical Application
• Shaft velocity sensor for ABS/traction
control
• Crank and cam shaft position sensors
Sensor Schematic
Installed on CV axle
http://www.me.gatech.edu/mechatronics_lab/Projects/Spring07/Group1/dorthy
6.JPG
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ME8843
Interfacing Concerns
• Emf is proportional to rate of change of
magnetic flux.
– Dictates ferrous material must be moving for
sensor to generate signal.
• Output voltage is dependent on velocity of
toothed wheel
– Performance may be reduced at slow speeds
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Ultrasonic Transducer
• Ultrasonic transducer (piezoelectric transducer)
is device that converts electrical energy into
ultrasound
• Upon receiving sound echo (pressure wave)
back from surface, ultrasound transducer will
turn sound waves into electrical energy which
can be measured and displayed
• Ultrasound are sound waves above normal
range of human hearing (greater than 20K
hertz).
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Since piezoelectric crystal generates voltage when force is
applied to it, same crystal can be used as an ultrasonic
generator and detector
 Some systems use separate transmitter and receiver
components while others combine both in single
piezoelectric transceiver
Alternative methods for creating and detecting ultrasound
include magnetostriction and capacitive actuation.
Pulse echo
sensor
Transmit-Receive
sensor
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• Sound is transmitted through propagation of
pressure in air
• Speed of sound in air is normally 331 m/sec at
0oC and 343 m/sec at 20oC for dry air
• Digital signal processor embedded in sensor
calculates distance between sensor and object
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 X = vsound . t
 Where:
 Vsound is known
 t = 0.5 (time of flight)
 X is distance between sensor head and object
 Range of sensor varies between 5 cm to 20 m
 Sensor is not appropriate for very short distance
measurements
 Frequency response (distance measurement
update rate) varies with distance measured
– In general, it is about 100 Hz
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• Piezoelectric crystals have property of changing
size when voltage is applied
• Applying alternating current (AC) across them
causes them to oscillate at very high frequencies
– Producing very high frequency sound waves
• Ultrasonic sensors work on principle similar to
radar or sonar
–Radar and Sonar evaluate attributes of target
•Interpreting echoes from radio or sound waves
respectively
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Applications
ME8843
Medical:
 Medical ultrasonic transducers (probes):
 Come in variety of different shapes and sizes for
use in making pictures of different parts of body
 Transducer may be:
 Passed over surface of body or
 Inserted into body opening such as rectum or
woman’s reproductive organ
 Clinicians who perform ultrasound-guided procedures
often use probe positioning system to hold the
ultrasonic transducer.
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 Technology can be used for measuring:
– wind speed and direction (anemometer),
– speed through air or water
– fullness of tank
– amount of liquid in tank
• sensor measures distance to surface of fluid.
• Other applications include:
– in robots for obstacle avoidance
– burglar alarms
– non-destructive testing, and etc
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Laser Ultrasound System
• Nd:YAG pulsed laser:




Repetition rate: 20 Hz
Pulse Width: 10 ns
Pulse Energy: 45-450 mJ/pulse
Beam Diameter: 6 mm
Control
Box
Nd:YAG
Laser
 Positioning Stage:
 Resolution: 50 μm
 Electro-Magnetic Acoustic
Transducer (EMAT):
 Bandwidth: 200 kHz-2.5 MHz
 Data Acquisition Card:
 Resolution: 14 bit
 Sampling Rate: 125 MHz
Positioning
Axis-lead screw
EMAT and
Preamp
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Data Acquisition
and User Interface
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Automated Weld Inspection System
 System consists of laser, beam delivery subsystem, stepper motor driven
linear screw, electromagnetic acoustic transducer (EMAT), data
acquisition card, computer software, and control unit
 Generated ultrasounds traveling through weld seams are received by
EMAT
 System resolution not yet determined, but has been used to detect 0.4
mm void
 Used system to inspect 180 mm long weld bead at 1 mm increment in 26
secs Lens
Mirror 3
Mirror 2
Beam Delivery
 Type of defects: Lack of penetration; Blow hole; and Short leg
Sample
Incident Laser Beam
EMAT
Mirror 1
Preamp
Laser
Advanced
Linear Screw Georgia Tech
Mechatronics,
EMAT
ME8843
Identifications of Solder Bump
Defects in Chip Packages
Examples of Emerging Microelectronic Packages:
3-D Packaging: Stacked Die
Chip Scale Package
Quad Flat Package (QFP)
Total Bumps: 560
Flip Chip
Ball Grid Array (BGA)
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Amkor Super BGA
Optical
Micrographs of Good and Bad Solder
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Bump Cross Sections
Good Solder Bump
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Two medium size voidsAdvanced
near the interface
Head-in-Pillow defects
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Poor wetting, an intermittent
connection
Optical micrographs of Good and Bad Solder
Bump Cross Sections
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Pad crater with crack initiating at the trace
Crack initiates at the edge of the pad
Inspection of solder bumps is crucial process in
microelectronics manufacturing industry.
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Intelligent Laser Ultrasound Inspection System
ME8843
Laser Beam Delivery:
•High-quality fiber face polish with fiber
injection optics
•Stable laser injection optical mount
•Rugged, rubber/metal fiber jacketing
•Variable excitation spot (0.6-8.0 mm2)
•Excitation standoff distance > 50 mm
A
Fiber-coupled sensor head
•16 mm aperture
•3 μm minimum spot diameter
•Variable standoff distance via
autofocus system
B
DVT SmartImage Sensor
•PC programmable stand-alone image processing
sensor
•Fiducial coordinates sent to PC through serial
port
•640 x 480 pixel resolution, 8–bit grayscale CCD
•1/10 th pixel software resolution, 5 mm viewing
C
window
•Possible sub-micron resolution
Model: New Wave Research Polaris II
Wavelength: 1064 nm or 532nm with SHG
Repetition Rate:1~20 Hz variable
Pulse Width: 4-5 ns
Pulse Energy: 45mJ/pulse, optical attenuator
adjustable
D
Typical Data Acquisition Parameters
•Sampling rate: 25 MHz @ 12-Bit res.
•Trigger source: Laser output
•Sample depth: 2048 samples (~ 82 μsec
@ 25 MHz)
•Voltage Range: ±100 mV (~ ±5 nm)
•Signal Averaging: 4–128 avgs. E
•High stiffness, preloaded bearings
•Integral X/Y table designed with wide
base to increase stiffness
•Higher bidirectional repeatability (< ±6
μm,)
•Larger mounting surface (326 x 326 mm)
F
•Larger travel (200 x 200 mm)
•Stiff, pre-loaded linear motion
components
•Linear encoder measurement (1μm res.)
•High precision (±10 μm)
G
Polytec Laser Doppler Vibrometer
•Heterodyne interferometer capable of
displacement measurements
•50 nm/Volt analog output
•150 nm full scale output (peak to peak)
•Operating Frequency Range: 50 kHz to 25
MHz
•Lower cutoff frequency: 25 kHz (-3 dB),
H
rolloff 40 dB/dec
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Vibrometer Autofocus System
•Hands free autofocus system to increase
repeatability and throughput
•Customizable focusing algorithms for
different kinds of chip package
•Remote operable
•Serial interface with MATLAB for fully
automated testing
I
•Average refocus time: 3 sec
ME8843
Laser Ultrasound Inspection (LUI) System
3 US Patents Have Been Issued & 2 Pending
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Photo Interrupt
• Uses emitter and detector
photo diode pair
• With no obstruction
detector is high
• When an object blocks the
light the detector is low
• Advantages
– Simple to interface
– Inexpensive
– Reliable
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Photo Interrupt
Types
• Wide variety of packages
and orientations
• Types
– Logic (digital ±5 volts)
– Transistor/diode (analog)
• Manufacturers
– Fairchild
– Honeywell
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Photo Interrupt
Applications
• Encoder wheel for angular
measurements.
• Computer mouse with a ball
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Photo Interrupt
Applications
• Detect holes or slots for
positioning of liner slides
– Elevators
• Detect the location of
products on and assembly
line
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Pressure Sensors
• Used to detect pressure of
fluids or gasses.
• Technologies (many)
– Strain gage
– Piezoresistive
– Microelectromechanical
systems (MEMS)
• Each sensor has a pressure
range that it works in.
• Most have analog outputs
that need amplification
– Some have built-in amplifiers
for direct connection into
microcontroller
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Pressure Sensors
Types
• Differential Pressure
– Difference between two or more
pressures introduced as inputs
to the sensing unit
– 2 input
• Absolute/Gage Pressure
– The pressure relative to perfect
vacuum pressure or set
pressure (like pressure at sea
level)
– 1 input
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Pressure Sensors
Applications
• Measure pressure of gas or fluids
• Measure altitude
– For plains or weather balloons
• Measure flow
– pressure sensors in conjunction
with the venturi effect to measure
flow
• Measure depth of water
– When measuring liquids, most
sensors are not rated to have
unclean liquids contact the sensor
components. A small amount of air
in the tube right before the sensor
will create a barrier from the liquid.
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Accelerometers
• Used to measure acceleration
– Common SI units
meters/second2 (m/s2) or
popularly in terms of g-force (1 g
is earth’s gravity)
• At rest an acceleration will
measure 1 g in the vertical
direction
• They can come in 1, 2 or 3
axis configurations
– With 3 axis it gives a vector of
the accelerations direction (after
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accounting Advanced
for gravity)
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Accelerometers
• Because of earth’s gravity, the
sensor will read 1 to 0 g as the
sensor is rotated from being
vertical to horizontal.
– This can be used to measure
angle the of tilt
• Each sensor has a range that
it works in.
• Most have analog outputs that
need amplification
– Some have built-in amplifiers for
direct connection into
microcontroller
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Accelerometers
How they work
• Mechanically the accelerometer
behaves as a mass-damper-spring
system
– Many use Microelectromechanical
systems (MEMS). Which use very small
cantilever beams with masses on them
• Under the influence of gravity or
acceleration, the proof mass deflects
from its neutral position.
• This deflection is measured in an
analog or digital manner
– Commonly the capacitance between a
set of fixed beams and a set of beams
attached to the proof mass is measured.
– Integrating piezoresistors in the springs
to detect spring deformation is another
method
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Accelerometers
Applications
• Can be used to sense
orientation, vibration and
shocks.
• Used in electronics like the Wii
and iPhone for user input.
• Acceleration integrated once
gives velocity, integrated a
second time gives position.
– The integration process is not
precise and introduces error into
the velocity and position.
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