Download Slide 1

• Introduction
• Position Sensors
–Linear
–Rotary
–Capacitive
• Level Sensors
Mechanical
Sensors
–Thermal
–Ultrasound
• Stress & Strain
• Accelerometers
• Piezoelectric Effect
• Microphones
• Pressure sensors
• Flow sensors
• Doppler Effect
• Hall Effect
1
Breadth and Depth of this
one subject
Sensors Volume 7
2
Manufacturers
of Mechanical
Sensors
http://www.eurosensors.cz/techprogramme.html
http://www.sensorsportal.com/HTML/SENSORS/MechSens_Manuf.htm
3
Position sensors
http://content.honeywell.com/sensing/prodinfo/solidstate/
•
•
•
•
Potentiometric
Capacitive/Inductive
Variable Reluctance
Level
–
–
–
–
mechanical
electrical
ultrasonic
pressure
Typical Applications:
•Ignition timing
•Power sensing
•Valve position
•Robotics control
•Current sensing
•Linear or rotary motion
detection
•Length measurement
•Flow sensing
•RPM sensing
•Security systems
4
5 kohms
6 to 48 inches extension
can be purchased.
5
Linear Transducers
Injection molding machine clamping, injection, and
ejection control: This process is set up as closed
loop feedback and monitored continuously. The
location of the moving mold head, the auger feeding
the plastic, and the ejector position are all
monitored by continuous output potentiometer
position sensors. The rugged LONGFELLOW and
SHORT LONGFELLOW position sensors are used
extensively on machines world wide.
Printing press roll alignment for multicolored images: When you see
a clean, clear, sharp, multicolored image in your newspaper,it may
have been controlled by a three (3) inch Short Longfellow. Many
printing rolls use Short Longfellows to provide the control signal for
continuous rapid dynamic alignment.
Longfellow applications
6
http://www.polytecpi.com/capsens.htm
Capacitive sensors and flexure stage
with integrated capacitive sensors
Ranges up to 300 µm with 0.1 nm
resolution.
Integrated Linearization system (ILS)
provides 0.05% linearity. Features of
•Highest resolution (<0.1 nm) of
commercially available displacement
sensors.
•Measuring ranges of 15, 50, and 100
µm (45, 150, and 300 µm with slightly
reduced accuracy).
•Extremely high long term stability
(<0.1 nm / 3 hours).
•Up to 3 kHz bandwidth
•Invar versions for highest
temperature stability (5 X 10-6 / °K)
•Stand-alone and modular
electronics
Capacitive Sensors
7
A
C  K 0
d
d
K = dielectric constant
ε0 = permittivity = 8.85 pF/meter
A = area of one plate
d = distance between plates
A
Film-Foil Capacitor Contstruction
Measuring
Capacitance
8
dvC (t ) The Derivative of a function is its SLOPE
iC  C
1
dt
ZC 
1
j

C
vC   iC (t )dt
The Integral of a function is its AREA
C
There are many ways to measure capacitance. One common way involves
putting a current into the object (or a commercial capacitor), and seeing
how long it takes to reach a certain voltage. The longer it takes to reach a
particular voltage, the higher the capacitance.
Another way is to use a bridge circuit, which work a lot like a balancebeam for capacitance.
Measuring Capacitance
9
Z1ZX=Z2Z3
Z2
Z1
Using the designations in the figure:
1
1
R1 ( RX 
)  R2 ( RS 
)
j C X
j C S
ZS
Zz
Multiply _ this _ out _ and _ if
R1 RX  R2 RS
then
R1 C X

R2 CS
http://www.tpub.com/neets/book16/66e.htm
AC Bridge
10
Applications
•Liquid Level Control for both
explosive and non-explosive materials.
•Package Inspection for product
content and/or fill level.
•Wire-Break Detection for wire sizes
down to .003".
•Plastic Pellet Detection in a hopper
for injection molding processes.
•Grain or Food Products Level
Detection; intrinsically safe models
available.
•Small Metal Parts Detection; greater
sensing range than comparable
inductive sensors.
http://www.turck-usa.com/literature/index.htm
Turck Capacitive Sensor
11
The active element is
formed by two metallic
electrodes positioned
much like an “opened”
capacitor (Figure 1).
Electrodes A and B are
placed in a feedback loop
of a high freq. oscillator.
When no target is present,
the sensor’s capacitance
is low & the oscillation
amplitude is small. When a
target approaches the face
of the sensor, the
capacitance increases.
This results in increased
amplitude of oscillation.
The amplitude of
oscillation is measured by
a circuit that generates a
signal to turn on or off the
output (Figure 2).
Turck Capac. Sensor
12
A capacitive level sensor
The capacitance-based liquid level sensor is typically
manufactured of 3/8 inch OD stainless steel tubing and
will operate with virtually all cryogenic liquids including
nitrogen, carbon dioxide, liquified natural gas, argon,
neon, and other cryogenics. Upon request, special
assembly techniques can be applied for sensors
required for liquid oxygen or hydrogen measurement.
Cryogenic: of or relating to the
production of very low temperatures
http://www.americanmagnetics.com/level/sensors.html
13
Other Level Sensors
•
•
•
•
•
Thermal Differential
Mechanical
Temp
Of
Electrical
Gas
Ultrasonic
Pressure
Temp
Of
Liquid
RTD’s
14
• Thermal point level switch for
the detection of level in all
vessels.
• Wide operating temperature
range -100°F to +850°F.
• Switch on level change of .03
inch without concern for
changing temperature,
density, detective constant or
http://www.sag-automation.com/ls3100.html
chemical composition.
• Removable, plug-in
electronics
• Free of all moving parts that
can stick, coat or fail.
• Fast response time of .1 to 1
second on wetting, media
dependent.
Thermal Differential
Sensor
Response Time: The time a system
or functional unit takes to react to
a given input.
http://www.its.bldrdoc.gov/fs-1037/dir-031/_4584.htm
15
Thiokol Propulsion's electronic propane fuel level sensors can be designed for a
variety of tank configurations, either for an infinite variety of vehicles or
stationary storage and dispensing tanks. Most of the issues facing the
emerging alternate-fuel vehicle market revolve around driver convenience.
Fuel Level Sensor
Thiokol Propane fuel
level sensors
16
• Operates by transmitting a series of
Applications
• Non-contact level
measurement
• Tank level measurement
• Proximity/distance
measuring
• Snow depth sensor
ultrasonic sound waves in a cone shaped
pattern
• Sound waves reflect from target back to
sensor, which measures the time interval
between transmitting and receiving the
sound wave.
• Calculated by the speed of sound, the time
interval is converted to a distance
measurement.
• 18 programmable modes
• Can be adjusted to meet the requirements
of various monitoring sites
• Programmable modes include sensitivity,
calibration, signal averaging, and pulse
control.
http://www.sutron.com/products/sensors/waterlevel/5600-0157.htm
Ultrasonic Sensor
17
http://www.ultrasonicsensors.com/technolo.htm
Range: Compact and Modular models as close as 5 cm (2 inches) and as
far as 1128 cm (37 feet), other models vary.
Power Input: DC all models, AC input options available for Modular
sensors
Beam Angle: Conical shape, 15 degrees total angle unless otherwise
noted
Adjustment: All models are push-button adjustable for basic setup.
Compact and Modular sensors are additionally PC configurable using
SoftSpan™.
Update Rate: 20 Hz nominal, adjustable from 2 to 120 Hz on PCconfigurable models Ultrasonic Frequency: 50 kHz
Ultrasonic Example
18
http://www.measure.demon.co.uk/Acoustics_Software/speed.html
Speed of sound at sea level 250 C
and 25% humidity: 346.71 M/sec
20 feet
m
in 1 ft
ft
346.71
 36.37 
 1051
sec
m 12 in
sec
1 sec
 40 ft  .03807 sec
1051 ft
Ultrasonic Example
19
L
L
1N
1Pascal  2
M
http://fermi.bgsu.edu/~stoner/p201/shm/sld002.htm
Force
l
R 
A
l
R  2 R0
l0
Stress and Strain
GND
DMM
Force
20
The output voltage of a bridge
circuit is given as follows.
http://www.tokyosokki.co.jp/e/product/strain_gauge/what_strain.html
Wheatstone Bridge
Strain Measurement
http://bits.me.berkeley.edu/beam/sg_1.html
21
• A load cell is a force transducer. This
device converts force or weight into an
electrical signal.
• The strain gage is the heart of a load
cell. A strain gage changes resistance
when it is stressed. These gages are
developed from an ultra-thin heattreated metallic foil and are chemically
bonded to a thin dielectric layer. "Gage
patches" are then mounted to the
strain element with specially
formulated adhesives.
•The precise positioning of the gage,
the mounting procedure, and the
materials used all have a measurable
Force
effect on overall performance of the
load cell.
Multiple strain gages are connected to create the four legs of a Wheatstone-bridge
configuration. When an input voltage is applied to the bridge, the output becomes
a voltage proportional to the force on the cell. This output can be amplified and
processed by conventional electrical instrumentation.
Load Cell
Principles
22
Maximum Excitation: 15V DC
Load Cell
Capacities 250 lbs. to 15,000 lbs.
Safe Overload 150 %
Full Scale Output 3 mv/v + or - 0.25%
Non- Linearity < 0.03 % FS
Hysteresis < 0.02 % FS
Non Repeatability < 0.01 % FS
Thermal Sens. Shift 0.0008% of reading
Thermal Zero Shift 0.0015% FS/deg. F
Bridge Resistance 350 ohms
http://www.massload.com/brochure_-_ml200.pdf
23
x  position
dx
v
 velocity
dt
2
d x
a  2  acceleration
dt
  angularpos ition
Position,
Velocity, &
Acceleration
  2   F
v(t )  sin( t )
dv(t )
  cos(t )
dt
d

 angularvelocity
dv(0)
  cos(0)
dt
dt
2
d 
  2  angularacc eleration dv(0)  
dt
dt
24
x   v(t )dt  v(0)
v   a(t )dt  a(0)
a  acceleration
Integral
Relations
Newton’s Law
F=Ma
Volt (t )  sin( t )  accel.
1
 Volt (t )dt   cos(t )  V (0)  v

1
 Volt (t )dt   
2
sin( t )  V (0)  t  v(0)  x
25
When it comes to being first over the finish line, Entran's
MotorSport Racing Accelerometers have been there time and
again. Entran's more than 20 years of experience in
Formula I racing have produced an accelerometer series
that has been custom tailored to the needs of Auto Racing
Teams and can withstand the rigors and tough environment
of motorsports. With integral overrange stops to survive
high vibration levels, onboard EMI/RFI filtering for a clean
signal, high level viscous damping to eliminate resonance,
all in a compact size, the EGRH provides a winning
performance for numerous measurements throughout the
vehicle. The EGRH is part of Entran's large family of
MotorSport Racing Sensors for F1, GTS, ALMS, CART, IRL
and NASCAR.
http://www.entran.com/egr.htm
Racing
Accelerometer
26
The Piezoelectric effect is an effect in which energy is converted between
mechanical and electrical forms. It was discovered in the 1880's by the
Curie brothers. Specifically, when a pressure (piezo means pressure in
Greek) is applied to a polarized crystal, the resulting mechanical
deformation results in an electrical charge. Piezoelectric microphones
serve as a good example of this phenomenon. Microphones turn an
acoustical pressure into a voltage. Alternatively, when an electrical
charge is applied to a polarized crystal, the crystal undergoes a
mechanical deformation which can in turn create an acoustical
pressure. An example of this can be seen in piezoelectric speakers
which are the cause of those annoying system beeps that are all too
common in today's computers.
http://ccrma-www.stanford.edu/CCRMA/Courses/252/sensors/node7.html
http://www.imagesco.com/articles/piezo/piezo01.html
Piezoelectric Effect
27
•
•
•
•
Carbon: Carbon microphones are made by encasing lightly packed carbon granules in
an enclosure. Electrical contacts are placed on opposite sides of the enclosure. When an
acoustical pressure is exterted on the carbon granules, the granules are pressed closer
together which decreases the measured resistance. This is a very low quality acoustic
transducer, but is still used in telephone handsets.
Capacitor (condenser): Capacitor microphones are made by forming a capacitor between
a stationary metal plate, and a light metallic diaphragm. When an acoustical pressure
impinges on the diaphragm, the diaphragm moves and causes the distance between it
and the stationary plate to change. This changes the capacitance of the device. To
measure the capacitance, one must apply a current. When this is done, the change in
capacitance will result in a change in the voltage measured across the device.
Electret and Piezoelectric: Electret microphones are capacitor microphones which use
an electret material between the plates of the capacitor. Electrets are materials with a
permanent polarization, and hence surface charge. Many high quality, low cost electret
microphones are available currently. As discussed previously, piezoelectric crystals are
crystalline structures which are similar to electrets in that they exhibit a permanent
polarization of the individual cells. It is possible to use piezo sensors as microphones as
well. Since they are in the form of a thin film, they are very useful if one is interested in
detecting surface vibrations of an object.
Magnetic (moving coil): Moving coil, or dynamic microphones are based upon the
principle of magnetic induction. When an electrical conductor is moved through an
electric field, a voltage is produced. This voltage is proportional to the velocity of the
conductor. A moving coil microphone is made by attaching a coil of wire to a light
diaphragm which moves in response to acoustical pressure. The coil of wire is
immersed in a magnetic field, hence the movement of the coil in the magnetic field will
create a voltage which is proportional to the acoustical pressure.
http://ccrma-www.stanford.edu/CCRMA/Courses/252/sensors/node6.html
Microphone Types
28
• Pressure sensors contain sensing elements that consist of four
piezoresistors buried in the face of a thin, chemically-etched silicon
diaphragm. A pressure change causes the diaphragm to flex, inducing
a stress or strain in the diaphragm and the buried resistors. The
resistor values change in proportion to the stress applied and produce
an electrical output. We offer three pressure sensor measurement
types—absolute, differential and gage—including vacuum gage and
bidirectional types.
• Pressure ranges from 0.5 in H2O up to 30 psi.
Typical Applications
Medical equipment: respiration, dialysis, infusion pump
HVAC, data storage, and gas chromatography equipment
Process controls
Industrial machinery
Pumps
Robotics
Off-road applications
http://content.honeywell.com/sensing/prodinfo/pressure/
Pressure Sensors
29
http://www.automationsensors.com/frames/indexFL.html
Flow
30
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/radar.html
Doppler Effect
31
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp2.html#c1
Source Approaching
Source Receding
Doppler Calculations
velocity
v
f source 

wavelength 
v
f returned 
 f source
v  vs
f returned
v

 f source
v  vs
32
Hall Effect
33
Programmable Linear Hall Effect Sensor
Applications
contactless potentiometers
rotary position measurement
linear position detection
magnetic field and current measurement
34
Linear Hall Effect Sensor
Summary
Introduction
Position Sensors
Level Sensors
Accelerometer
Piezoelectric
Microphones
Pressure
Flow
Doppler Effect
Hall Effect
35