transducers and sensors
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Advanced Mechatronics, Georgia TechAdvanced Mechatronics, Georgia Tech
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ME 6408Advanced MechatronicsInstructor: Professor I. Charles Ume
Hall effect SensorsVariable Reluctance Sensor
Ultrasonic Sensors (Sonic Distance Sensors)Photo Interrupt
Pressure SensorsAccelerometers
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ME8843ME8843 Hall Effect Sensors
• Developed by Edwin Hall in 1879; and hence the name Hall effect
• Used to:– provide noncontact
means to detect and measure magnetic field
http://farm1.static.flickr.com/62/227729006_fab88c1668.jpg?v=0
Hall Effect Sensor Sensing a Shaft Speed
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How they work• Presence of magnetic field
deflects electrons flowing through conductive material
• 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/Hall_effect_A.png
Depiction principle of the Hall Effect
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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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ME8843ME8843 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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Packaging and Manufacturers
• ICs– Analog Devices:
• AD22151G from Analog Devices
– Allegro MicroSystems, Inc.• Wide range of linear, latching and
switching sensors• Great sampling policy
– Many, many more
• Packaged units– Honeywell– Many, many more
http://sensing.honeywell.com/client_asset/document/1/5/4/0/3/5/document_C3697B35-
C930-CB7C-FE090DFFCE61FB22.jpg
http://www.allegromicro.com/en/Products/Part_Numbers/1120/pinout.gif
SOT23
SIP
Hall Effect Sensor Module
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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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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.)
http://www.motionsensors.com/railwithoring2.jpg
Industrial Variable Reluctance Sensor
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ME8843ME8843How 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
http://www.instronics.com/images/sensoronix/image.ds.drawing.vr.jpg
Variable Reluctance Sensor Construction
Typical Configuration
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Typical Application• Shaft velocity sensor for ABS/traction
control
• Crank and cam shaft position sensors
http://www.me.gatech.edu/mechatronics_lab/Projects/Spring07/Group1/dorthy6.JPG
Sensor Schematic Installed on CV axle
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ME8843ME8843Interfacing 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 (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).
Ultrasonic Transducer
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ME8843ME8843Since 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 transceiverAlternative 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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ME8843ME8843 Applications
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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ME8843ME8843 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
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
Data Acquisitionand User Interface
PositioningAxis-lead screw
Nd:YAGLaser
ControlBox
EMAT and Preamp
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ME8843ME8843 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 Type of defects: Lack of penetration; Blow hole; and Short leg
Laser
Beam Delivery
EMATLinear Screw
Sample
EMAT
Preamp
Incident Laser Beam
Mirror 1
Mirror 2Mirror 3Lens
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ME8843ME8843 Identifications of Solder Bump Identifications of Solder Bump Defects in Chip PackagesDefects in Chip Packages
3-D Packaging: Stacked Die
Ball Grid Array (BGA)
Flip Chip
Chip Scale Package
Examples of Emerging Microelectronic Packages:Examples of Emerging Microelectronic Packages:
Total Bumps: 560
Amkor Super BGA
Quad Flat Package (QFP)
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ME8843ME8843Optical Micrographs of Good and Bad Solder Bump Cross Sections
Two medium size voids near the interface Poor wetting, an intermittent connection
Head-in-Pillow defectsGood Solder Bump
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Crack initiates at the edge of the pad
Pad crater with crack initiating at the trace
Inspection of solder bumpsbumps is crucial process in microelectronics manufacturing industry.
Optical micrographs of Optical micrographs of Good and Bad Good and Bad Solder Bump Cross SectionsSolder Bump Cross Sections
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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
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
window• Possible sub-micron resolution
Model: New Wave Research Polaris II Wavelength: 1064 nm or 532nm with SHG
Repetition Rate:1~20 Hz variablePulse Width: 4-5 ns
Pulse Energy: 45mJ/pulse, optical attenuator adjustable
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.
•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)
•Larger travel (200 x 200 mm)
•Stiff, pre-loaded linear motion components•Linear encoder measurement (1μm res.)
•High precision (±10 μm)
Fiber-coupled sensor head•16 mm aperture
•3 μm minimum spot diameter•Variable standoff distance via
autofocus system
A CB
E
F
G
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
•Average refocus time: 3 sec I
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),
rolloff 40 dB/decH
D
Intelligent Laser Ultrasound Inspection SystemIntelligent Laser Ultrasound Inspection System
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ME8843ME8843Laser Ultrasound Inspection (LUI) System3 US Patents Have Been Issued & 2 Pending3 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 InterruptTypes
• Wide variety of packages and orientations
• Types– Logic (digital ±5 volts)– Transistor/diode (analog)
• Manufacturers – Fairchild– Honeywell
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Photo InterruptApplications
• Encoder wheel for angular measurements.
• Computer mouse with a ball
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Photo InterruptApplications
• 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 SensorsTypes
• 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 SensorsApplications
• 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 accounting 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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AccelerometersHow 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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AccelerometersApplications
• 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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