Applications
Applications for velocity measurement include:
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Controlling the speed at which metal stock is fed into a machine
tool.
Measuring the approach speed of a robotic tool onto its target.
Monitoring the speed of a generator in an electric power station.
An airport radar system measuring the speed of an approaching
aircraft using the Doppler effect.
Measuring an automobile’s wheel speed in order to provide
feedback to an antilock brake system.
Classification
Utilizing Differentiation of Displacement
Linear Velocity Transducer (LVT)
Reference Based
Conversion of Linear to Rotational Velocity
Measurement
Doppler Shift
Linear Velocity
Light Interference Methods
Measurement
VISAR System
Seismic Devices
Absolute
Gyroscopes
Velocity
Velocity
Tachogenerator
Measurement
Photoelectric Tachometer
Tachometers
Strain Gauge Tachometer
Switch Tachometer
Angular Velocity
Measurement
Relative
Rotating Magnetic Sensor
Velocity
Optical Sensor
Counter Types
Hall Effect Sensor
Wiegand Sensor
Stroboscopy
Introduction
• Linear Velocity
definition : Time rate of change of position of the object.
Direction : direction of change in position
Type: Vector quantity
Magnitude : Speed
Common units : m / s ; miles / h
• Angular Velocity
definition : Time rate of change of angular position of the object.
Direction : direction of the axis about which
the object is turning
Type : Vector quantity
Magnitude : Rotational speed
Common units : RPM (revolution per minute)
Measurement of Linear Velocity
• A precise theory
v2
y2
v1
y1
average speed =
v y = ∆t lim 0
∆y dy
=
∆t dt
t
t1
t2
v y (t ) = v i + ∫ a y (t ) dt
ti
• Methods
- Reference Based methods
- Seismic devices
y 2 − y1 ∆y
=
t 2 − t1
∆t
Reference Based Methods
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Definition : Measurements made in which the instrumentation has
components on both the moving object and the
reference frame for the measurement.
Methods include measuring through:
– Differentiation of displacement
– LVT
– Conversion of Linear to angular velocity
– Doppler effect sensors
– Light interference methods
– VISAR system
Utilizing differentiation of displacement
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Method : Using some type of position transducer to record the
position-time function of the moving object and then
differentiate this function to get speed-time function.
Example : Two pickups spaced a known distance apart; recording the
time for the object edge to pass between the pickups.
Result : average speed
Application : Determining the muzzle speed of a projectile.
Notes :
–Selection of an acceptable transducer; Range, Resolution
and mass loading are important parameters.
–Because differentiation is a noise generating process,
particular care must be exercised to minimize the noise of
displacement.
Linear Velocity Transducer
• Basis : Linear Generator
• Theory : When a coil cuts the magnetic
field lines around a magnet, a voltage is
induced in it.
ei ∝ BLV
• Displacement range : 0.5 to 24 inches
mv
• Typical sensitivity range : 40 to 600 ips
• Manufacturers : Trans-Tek
ei = induced voltage in the coil
B = magnetic field strength
L = length of wire in the coil
V = speed of the coil relative to the magnet
Robinson Halpern
Macro Sensors
GE Co.
Conversion of Linear to Rotational
Velocity
• Method : Placing a rack on the moving object and having the
rack drive a pinion gear
• Example : same principle is used in automobile’s speedometer
Doppler Effect Sensors
• Theory : Doppler Shift
• Method : Transmitting a wave to
moving object and receiving it back.
• Applications :
fD =
2 V Cosθ
λ
‫ ـــ‬Weather broadcast
‫ ـــ‬Automatic emergency
break of car. (VORAD)
• Manufacturers :
‫ــ‬Canon
‫ــ‬Baron Services
Light Interference Methods
• Theory:classical Michelson Interferometer
• Method : a beam of monochromatic light is
split into two beams; one is directed onto a
stationary mirror, the other onto the target.
The super position of reflected beams is
directed to the lens, pin hole and then
counter.
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•Manufacturer : Polytech
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Advantages : High accuracy
Constraints : Target should have a highly
polished surface and very little tilt during the
test.
Device name : Laser Doppler Velocimeter
VISAR System
• Basis : Interferometry
• Range of work : 100 m s to 10 km s
• Sensitivity : 100 to 400 fringes per m s
• Advantages : -Highly accurate
-working with specularly or diffusely
reflecting surfaces
-insensitive to target’s tilting
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•Manufacturer : Valyn International
Applications : Weapon technology
Mining technology
Space technology
Geophysical & planetary researches
Controlled fusion energy researches
Seismic Devices
• Structure : a mass attached to the
transducer base by a spring. The base
is attached to the surface whose motion
is desired.
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transducer as the secondary
transducer.
2) a velocity transducer as the
secondary transducer.
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Applications :
•Manufacturers :Wilcoxon Research Inc
Teledyne Brown Corp.
Nanometrics Inc.
Approach : 1) A displacement
– Earthquake studying
– Oil well logging and related works
Measurement of Angular velocity
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Classification :
Angular Velocity
Relative : measurements are taken
with respect to the base of the item being
measured.
Absolute : Reference of the measurement is
the earth
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Idea : Generating a pulse train or sine wave whose frequency is proportional
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Devices : Tachometers
to angular velocity.
Counter Type Sensors
Stroboscopes
Tachometers
1) Tachogenerator
● Basis : A rotating generator produces a voltage signal proportional to
the rotational velocity of the input shaft.
● DC generator : produces a
voltage level proportional to speed.
•AC generator : produces an ac output voltage with a
frequency proportional to speed.
•Manufacturers : GE Co. ; Kollmorgen motion Technologies ;
Micro Mo Electronics ; Tamagava Sieki ;
Hubner ; Magnetic SPA.
Tachometers
2) Photoelectric Tachometer
● Structure : A disk with reflecting
markings attached to the shaft. A
light source and a light detector.
● Output : a train of pulses whose
frequency is proportional to shaft’s
RPM.
Tachometers
3) Strain Gauge Tachometer
● Structure : A thin rod with a bonded
strain gauge attached. The end of the
rod has a small wheel that rests on the
dist attached to the shaft.
● Output : A sinusoidal waveform whose
frequency is proportional to the
RPM.
Tachometers
4) Switch Tachometer
● Structure : a rod and an offset disk
attached to the shaft.
● Output : a train of pulses whose
frequency is proportional to Rotational
velocity.
Counter Type Sensors
1) Rotating Magnet Sensor
● Structure : A magnetic pickup and a rotating
slotted disk of a ferromagnetic material.
● Advantage : No need of external power source
● Manufacturers :
Smith Systems
Optec Technology
Balluf
Daytronic Corp.
Celduc Inc.
Honeywell
Counter Type Sensors
2) Optical Sensor
● Structure : A light emitter and a light detector
● Note : The effect of external light sources
● Manufacturers :
Banner Eng. Corp.
Sharp
Aromat Corp.
Leuze electronic Co.
Dinel Co.
Counter Type Sensors
3) Hall Effect Sensor
− IB d
VH =
ne
● Theory : Hall Effect
● Application : Wheel speed sensor for anti lock
braking system
● Manufacturers :
Optec Technology Inc.
Allegro Micro
Cherry Corp.
Counter Type Sensors
4) Wiegand Effect Sensor
● Theory : Wiegand Effect
● Structure : Wiegand wire ; an alternative
magnetic field ; a coil
● Manufacturer :
HID Corp.
Stroboscope
● description : A source of flash light with adjustable frequency
● Manufacturers : BBE Corp.
Extech Instruments Corp.
Monarch Instrument Co.
Shimpo Instrument Co.
Conditioning Circuits
• For a Sensor whose output level is important
• For a sensor whose out put is a train of pulses or similar outputs.
Iran’s Market
Available sensors in Market :
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Tachometer : Model DT2235A ; produced by Shenzhen Sampo
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Hall Effect Sensor : Models UGN3503 for 1000 Tomans and UGN3113
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Optical Sensor : Models 1s58 ; produced by sharp ; for 500 Tomans and
Instrument Co.Ltd. ; for 40’000 Tomant ; imported and sold by Landa
Electronic.
for 500 Tomans ; produced by Allegro Micro ; imported and sold by Jahan
Kit Co.
SG23FF produced by Kodenshi of Korea ; the price is 500 Tomans and the
importer and seller is Jahan Kit Co.
Companies working in this field : Jahan Kit
Persian Electronic
Paya Electronic
Conclusion
● The problem of velocity measurement is somewhat different from that of
measurement of other quantities in that there is not a large number of transducer
types and transducer manufacturers from which to choose for a given problem.
Frequently, the problem is such that the person must use his/her knowledge of
measurement of other quantities and ingenuity to develop a velocity measurement
method suitable for the problem at hand.
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Velocity is often obtained by differentiation of displacement or integration of
acceleration.
● The most common idea for Velocity measurement is to generate a signal whose
frequency is proportional to the velocity. Making use of the effects of a magnetic
field is another idea. The other idea is to utilize the frequency shift or phase shift
of waves caused by motion.
I appreciate
your attention