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MOVEMENT Sensor

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Type of sensors

• potentiometer

• gravitational

• inductive

• Eddy Current

•magnetic• Magnetostrictive Detector

• Magneto-resistive

• effect Hall

• capacitive• optic

• ultrasound

• radar

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otentiometer sensor • otentiometer sensor can !e linear or rotary

• T"e sensor #or$ as a voltage divisor% in all of t"e case t"e sensor ispo#er supply #it" a voltage reference% t"e output is a voltagedepending !y t"e movement d

• V&Vref'd(D #"ere D is t"e ma)im movement*

• T"is sensor is !uild as a coil or a t"in film resistance

• T"e resolution of coil resistance sensor is give !y coil dimensionand !y #ire diameter

• T"e #ire diameter in all of t"e case is +*+,mm% a good accuracy is!y +*,

• Displacements sensed !y t"e angular potentiometers range fromappro)imately ,+° to over .+++/ for t"e multi-turn pots

• E)ample0 12-3-45-1,M 6analogical7% 12-E 8 digital output digital

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9ravitational Sensors

• 9ravitational-level transducer is used in a toilet tan$*

• :nclination detectors% #"ic" measure t"e angle from t"edirection to t"e Eart";s center of gravity

• T"is sensor can !e #it" digital output on off 6s#itc"7% or #it"analog output t"e angel is proportion to resistance*

• T"e s#itc" is made of a nonconductive 6often glass7 tu!e

"aving t#o electrical contacts and a drop of mercury• <"en t"e sensor is positioned #it" respect to t"e gravity force

in suc" a #ay t"at t"e mercury moves a#ay from t"e contacts%t"e s#itc" is open* 3 c"ange in t"e s#itc" orientation causest"e mercury to move to t"e contacts and touc" !ot" of t"em%

t"us closing t"e s#itc"*

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•To measure angular displacement #it" "ig"er resolution% amore comple) sensor is re=uired*•:t is called t"e electrolytic tilt sensor * 3 small slig"tly curved

glass tu!e is filled #it" a partly conductive electrolyte*

•T"ree electrodes are !uilt into t"e tu!e0 t#o at t"e ends% andt"e t"ird electrode at t"e center of t"e tu!e* 3n air !u!!le

resides in t"e tu!e and may move along its lengt" as t"e tu!e

tilts* Electrical resistances !et#een t"e center electrode and

eac" of t"e end electrodes depend on t"e position of t"e

!u!!le*• T"e electrolytic tilt sensors are availa!le for a #ide spectrum

of angular ranges ,+ - >+ °

3ngular Displacement

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3ngular optic sensor

• T"e detector is useful in civil

and mec"anical engineeringfor t"e s"ape measurementsof comple) o!?ects #it" "ig"resolution

• Hemisp"erical spirit levelmounted on a p-n ?unctionp"otodiode array* 3 s"ado#of t"e !u!!le in t"e li=uidis pro?ected onto t"e surface

of t"e p"otodiode array*• T"e outputs of t"e diodesare converted in to digitalform and cali!rated at

various tilt angles*

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Capacitive Sensorsd

AC ⋅= ε

h

c

bC ⋅=

ln

2πε

lane and cylindrical capacitor

T"e a!ility of capacitive detectors to sense virtually all materials ma$es t"em anattractive c"oice for many applications 3 typical capacitive pro!e operates

at fre=uencies in t"e .-MH@ range and can detect very fast-moving targets*

3 capacitive pro)imity sensor can !e "ig"ly efficient #"en used #it" t"e electrically

conductive o!?ects* T"e sensor measures a capacitance !et#een t"e electrode and t"e

o!?ect*

3 met"od of measurement is t"e comparative met"od* :s used t#o capacitor one is a

reference and t"e second is un$no#n capacitor* T"e output voltage depend !y t"e

ration !et#een t"em*

−⋅= 1

0

r

vref

C

C KV V

T"e operating principle of a capacitive gauge% pro)imity% and position sensors is

!ased on eit"er c"anging t"e geometry 6i*e*% a distance !et#een t"e capacitor

plates7 or capacitance variations in t"e presence of conductive or dielectric

materials* :n t"is type of sensor t"e "umidity affect t"e sensor #or$s% "umidity

variation #it" ,+ and >A at 4,BC introduce a error !y +%.A from ull Scale*

Conditionare

semnal

Cv

Cr

Vo

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D-A,+ :Seca 8 "ig" accuracy sensor

deformation0 metallic material -.4 micrometri(m(BC

silicon material A micrometri(m(BC

T"e dielectric constant is affected !y temperature% "umidity and pressure <:TH

,+ppm

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:nductive sensor 8 1VDT and FVDT• 3 magnetic flu) coupling !et#een t#o coils may !e altered !y t"e movement of

and o!?ect and su!se=uently converted into voltage* T"e !asic arrangement of

a multi-induction transducer contains t#o coils0 primary and secondary* T"eprimary carries ac e)citation (V ref ) t"at induces a steady ac voltage in t"esecondary coil* T"e induced amplitude depends on flu) coupling !et#een t"ecoils*

• One is t"e movement of an o!?ect made of ferromagnetic material #it"in t"eflu) pat"* T"is c"anges t"e reluctance of t"e pat"% #"ic"% in turn% alters t"ecoupling !et#een t"e coils*

8 1VDT 6linear varia!le differential transformer7 8 FVDT 6rotary varia!le differential transformer7

• T"e t#o secondary are connected in t"e opposed p"ase* <"en t"e core ispositioned in t"e magnetic center of t"e transformer% t"e secondary outputsignals cancel and t"ere is no output voltage* Moving t"e core a#ay from t"ecentral position un!alances t"e induced magnetic flu) ratio !et#een t"esecondaries% developing an output*

Vref

Vo

* *

T"e advantage0 is a non contact sensor t"e

output impedance is lo# t"e error and t"e noise

suscepti!ility is lo#% t"e sensor is solid

T"e disadvantage0 resolution of measurement is

!y micrometrical order

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Eddy Current SensorsT"is sensors use t"e electromagnetic induction principle*

T"e induction of a coil vary #"en a conductive o!?ect isplaced in "is magnetic field* :n t"e conductive o!?ect is

induced a magnetic currents #itc" affect t"e coil

inductivity*

Eddy 6circular7 currents produce a magnetic field #"ic"

opposes t"at of t"e sensing coil% t"us resulting in a

dis!alance #it" respect to t"e reference coil* T"e closert"e o!?ect to t"e coil% t"e larger t"e c"ange in t"e

magnetic impedance* T"e dept" of t"e o!?ect #"ere

eddy currents are produced is defined !y0

µρ π

δ

f

1=

Naturally% for effective operation% t"e o!?ect t"ic$ness

s"ould !e larger t"an t"e dept"* 9enerally% t"e

relations"ip !et#een t"e coil impedance and distance to

t"e o!?ect x is nonlinear and temperature dependent* T"e

operating fre=uency of t"e eddy current sensors rangefrom A+ $H@ to ,+ MH@*

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Transverse Inductive Sensor

•:t is useful for sensing relatively small displacements offerromagnetic materials

• 3 self-induction principle is t"e foundation for t"eoperation of suc" a transducer* <"en t"e pro)imitysensor moves into t"e vicinity of a ferromagnetic o!?ect%its magnetic field c"anges% t"us altering t"e inductance oft"e coil* T"e advantage of t"e sensor is t"at it is anoncontact device #"ose interaction #it" t"e o!?ect isonly t"roug" t"e magnetic field* 3n o!vious limitation ist"at it is useful only for t"e ferromagnetic o!?ects atrelatively s"ort distances*

• T"e pro)imity sensor is useful for measuring smalldisplacements only% as its linearity is poor in comparison#it" t"e 1VDT*

C I R C U I T

D E

I N T E R F A T A R E

~

L1

L2

~

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Magneto resistive Sensors• Magneto resistive 6MF7 sensors ma$e use of t"e magneto resistive

effect% t"e property of a current-carrying magnetic material toc"ange its resistivity in t"e presence of an e)ternal magnetic field

• T"e magneto resistive sensor is used as a pro)imity% position% orrotation detector% it must !e com!ined #it" a source of a magneticfield*

SS

N NN

MRS

N

S S

S

N

MFS cam !e used as a

incremental position sensor :S

:S "as t#o output #it" +B p"ase

differences% can !e used to detect t"e

direction and angle of rotation*

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Traductoare magnetostrictive 3 transducer #"ic" can measure displacement #it" "ig" resolution across long

distances can !e !uilt !y using magnetostrictive and ultrasonic tec"nologies *

T"e transducer is comprised of t#o ma?or parts0 a long #aveguide 6up to m

long7 and a permanent ring magnet * T"e magnet can move freely along t"e#aveguide #it"out touc"ing it* 3 position of t"at magnet is t"e stimulus #"ic" is

converted !y t"e sensor into an electrical output signal* 3 #aveguide contains a

conductor #"ic"% upon applying an electrical pulse% sets up a magnetic field

over its entire lengt"* 3not"er magnetic field produced !y t"e permanent

magnet e)ists only in its vicinity* T"us% t#o magnetic fields may !e setup at t"e

point #"ere t"e permanent magnet is located* 3 superposition of t#o fields

results in t"e net magnetic field% #"ic" can !e found from t"e vector

summation* T"is net field% alt"oug" "elically formed around t"e #aveguide%

causes it to e)perience a minute torsional strain% or t#ist at t"e location of t"e

magnet* T"is t#ist is $no#n as t"e <iedemann effect* T"erefore% electric pulses

in?ected into t"e #aveguide;s coa)ial conductor produce mec"anical t#istpulses #"ic" propagate along t"e #aveguide #it" t"e speed of sound

specific for its material* <"en t"e pulse arrives at t"e e)citation "ead of t"e

sensor% t"e moment of its arrival is precisely measured* One #ay to detect t"at

pulse is to use a detector t"at can convert an ultrasonic t#itc" into electric

output*

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Optic Sensor

3 digital optical encoder is a device t"at converts motion into a se=uence of digital

pulses* Gy counting a single !it or !y decoding a set of !its% t"e pulses can !econverted to relative or a!solute position measurements*

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Absolute encoder

T"e optical dis$ of t"e a!solute encoder is designed to produce a digital #ord t"at

distinguis"es N distinct positions of t"e s"aft* or e)ample% if t"ere are > trac$s% t"e

encoder is capa!le of producing 4A distinct positions or an angular resolution of

,*I+ 6.+(4A7 degrees* T"e most common types of numerical encoding used int"e a!solute encoder are gray and !inary codes

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Incremental encoder

:t consists of t#o trac$s and t#o sensors #"ose outputs are called c"annels 3 and G*

3s t"e s"aft rotates% pulse trains occur on t"ese c"annels at a fre=uency proportional

to t"e s"aft speed% and t"e p"ase relations"ip !et#een t"e signals yields t"e direction

of rotation* T"e code dis$ pattern and output signals 3 and G* Gy counting t"e num!er

of pulses and $no#ing t"e resolution of t"e dis$% t"e angular motion can !e measured*

T"e 3 and G c"annels are used to determine t"e direction of rotation !y assessing

#"ic" c"annels JleadsJ t"e ot"er* T"e signals from t"e t#o c"annels are a ,(I cycle

out of p"ase #it" eac" ot"er and are $no#n as =uadrature signals*

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Decoding transitions of 3 and G !y using

se=uential logic circuits in different #ays

can provide t"ree different resolutions of

t"e output pulses0 ,2% 42% I2* ,2

resolution only provides a single pulsefor eac" cycle in one of t"e signals 3 or

G% I2 resolution provides a pulse at

every edge transition in t"e t#o signals

3 and G providing four times t"e ,2

resolution* T"e direction of rotation

6cloc$#ise or counter-cloc$#ise7 isdetermined !y t"e level of one signal

during an edge transition of t"e second

signal* or e)ample% in t"e ,2 mode% 3&

#it" G &, implies a cloc$#ise pulse%

and G& #it" 3&, implies a counter-

cloc$#ise pulse* :f #e only "ad a singleoutput c"annel 3 or G% it #ould !e

impossi!le to determine t"e direction of

rotation* urt"ermore% s"aft ?itter around

an edge transition in t"e single signal

#ould result in erroneous pulses

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E)ample

• F+ACM4,3F

• F,43M.43C

• F+ACM,431• S4>++

• D4.++

• 1.++

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http://www.gesensing.com/

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31:C3T:E- Measurement of resistive sensor used for inclination

,NI,I>

In

VrefKe)

454

In

CDI+.G

,

4.

Iu

V,-

CDI+.G

,4

,.,,

CDI+.G

A

I

44+n

CDI+.G

>

,+

V,L

,++5

M.

CDI+A.G

,.

,.

,4

A4

,I,AI

,,,+

2,

:NH

,O,

2+

O++

2O

3GC

VEE

Vs("

,NI,I>

454

In

4u4

4u4

Vref

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Hand!oo$ of modern sensors

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31:C3T:E- read data from a optical sensor

++ 0 3&, increment counter ++ 0 G&, decrement counter

+, 0 3&, increment decrement

+, 0 G&+ increment counter

,+ 0 3&+ decrement counter

,+ 0 G&, increment counter

,, 0 3&+ increment counter

,, 0 G&+ decrement counter

1

11A ++

1

+

+

+ 1

1

1

! ++ +1 ++

1 +

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