02 position c 0
TRANSCRIPT
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Inductosyn Position-dependent mutual inductance (and thus signal
transfer) between two meander-like flat coils
Excitation:
current into the fixed scale, OR
current into the moving slider
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Inductosyn driven slider
* One rotor (slide) driven by current
tKUtutU == coscos)(cos 2
* Two rotors driven
)cos()cossincos(cos)(u)(u)(u 22212 =+=+= tKUttKUttt
== cos)2cos(2 KUpxKUU
Coarse scale: incremental, fine scale : measurement of phase
Mutual inductance
M ~cos
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Inductosyn - driven stator (scale)
sincos)(usinsin)(u 2221 tKUttKUt ==
tKUtKUtu == sin)sin(sin)sincoscos(sin)(3
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stator
rotor
stator
rotor
a) b)
Resolver Selsyn
Scott transformer (3 phase / 2 phase)
Conversion of selsyn signal to resolver form
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Sensors based on eddy currents
the depth of field penetration (attenuation to 1/e)
G
Zm
y
i~
a) b)
2
=
Difficult field penetration to conductors
(low resistivity => high eddy currents)
Used for detecting presence of conductive targets
(proximity switch)
!!!
Eddy currents in
the material
compensate the
external field
(Lenz law)
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Sensors based on eddy currents -construction
field concentration (focusing) :ferrite core, ev. magnetic shielding
The sensor in typical
threaded-cylinder shape
Metallic target
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Sensors based on eddy currents :
signal conditioning circuits
Bridge and transformer circuits (compensating sensor) resonant circuits LC-oscillator: f, Q
pulse driven - defectoscopy
low f: change of Re(Z)
high f: change of L
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Sensors based on eddy currents : applications
sensors of translational motion
binary sensors of position (proximity switch)
detection of vehicles (or any conducting objects - mines, cable,pipelines)
diagnostics
cracks
material composition
noncontacting
operation in presence of dirtiness
target conductive
for d > independent on target parameters
u2
um
u1
us
is
iw
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~
~
1
2
e)
~
d)
~ 1
2
b)
~
k)
~
h)
~
a)
~
g)
~
j)
~
l
c)
~
f)
~
i)
l
~
l)
Sensors based on eddy currents : applications
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Magnetostictive sensors of position
max. length up to 4 m (attenuation)
hysteresis 0.4 m linearity 0.02 %
elastic wave in ferromagnetic material .... v = 3000 m/s = 3m / ns (approx. 10x speed of sound in air)
Interaction of magnetic fields (current pulse + permanent magnet) creates pulse of mechanical strain
(Wiedemann effect ) propagating along the wire. Time of flight => position of permanent magnet
S N S N S NSN SN SN
Inductionpickup coil
Magnetostrictivewire
Magnet inmovablefloat
InnerTube
Outerguide tube Reflectionterminator
Strain pulse
Strain pulse Strainpulse
reflectedoff bottom
Inductionpickupsensesinitial andreflectedstrainpulses
A B C
Patriot
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Capacitive sensorsd
SC
=
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Capacitive sensors contdd
SC
=
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Capacitive sensor with variable
area of electrodes overlapping
-
1323
1323
CC
CC
+
dSC =
a)
b)
13
2
x
+xx
C C13 23+C13
C23
ratiometric measurement: influence ofd, eliminated
C i i i h i bl
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Capacitive sensor with variable
area of electrodes overlapping
2313
2313
V23213
21
232131
232131232131
u)()(
U,if
)()()(U)(U0)(U)(U
CC
CC
UCUuCUu
UUU
CUuCUuCjCjCjjCjj
VV
VV
+
=+=
==
===+
resolution: 1 m, uncertainty 5 m
a)
b)
13
2
x
x
x
x
+xx
C C13 23+C13
C13
C23
C23
1
2
u1
u ; u1 2
U1
U1
U1
u2
U2U2
U2
u3uv
uv
uv
3
P1
P2
Reg.
c)
td)
1 2
3
3
1 2
e)
f)
S
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Modern signal conditioning circuits for
capacitive sensors
Main problem -
influence of capacitance of leads (cable)
(driven from voltage source, current measured by ideal
ammeter )
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charge pump
realisation by CMOS technology and inductive dividers
coils and transformers are not necessary
C/f converter
ADC not necessary
converter C/U capacitor in feedback eliminates dependence on frequency
transformer bridges
expensive, noncompatible with IC
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+
Cp2
C1
Cp1 Cs
G
U (j )1
U (j )2 U(j )
-A
Linearity even for variable air gap sensor (vibration measurement),U2 ~ d
Amplifier for capacitive sensors:
Parasitic capacitances of the cable to Cs will not apply:
Cp1 is on virtual zero, Cp2 is on low output impedance of the OpAmp
Applications of capacitive sensors
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Applications of capacitive sensors
Honeywell
Omeg
Sensing humidity of
material in dryer
Sensing level of liquid dye in
printworks
Bottle
Conveyor
belt
Control of filling
drums
reservoir
Checking presence of parts
in product completionControl of filling
Typical applications:- sensing level in tanks
- checking filling of products
inside packages- sensing level of powder /
granules in storage
- sensing non-metalic objects
on conveyor belts
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Hone well
rubber gasket
sensor
Checking presence of products in mass production:
sensor
metal object