transducers and sensors

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


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


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


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


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


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


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


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


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


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)


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

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F

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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

•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


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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