Vishay Precision Group LVDT User manual

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Contents
INTRODUCTION
General............................................................. 1
Functions.......................................................... 2
Technicaldata................................................... 3

OPERATINGINSTRUCTIONS
General............................................................. 5
Potentiometers................................................. 5
Testsockets...................................................... 5

INSTALLATION
General............................................................. 7
Connections...................................................... 7
Set‐upprocedure.............................................. 7
Calibration........................................................ 8

FAULTFINDING
General............................................................. 11
Transducers...................................................... 11
Transducercables............................................. 11
Signalconditionermodule............................... 12
Cableswithload............................................... 13

APPENDICES
1.Tableofsettings
2.DeclarationofConformity




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
n
trod
G
eneral
g
ure1.
V
D3isasig
n
w
opositiont
o
sitionmea
s
h
eoutputsf
r
h
echannels
a
o
mthepow
e
h
ecompact
m
c
rewsonafl
a
h
roughone
p
o
cketsarea
c
uctio
n

n
alcondition
ransducers,
s
urement.
r
omeachch
a
a
regalvanic
a
e
rsupply.
m
oduleise
a
a
tsurface.
A
p
lug‐intermi
c
cessibleatt
n

ermodule,
d
typeLVDT,
t
a
nnelarean
a
llyisolated
a
silyinstalle
d
A
llelectrical
c
nalblockfo
r
hefrontpa
n
Figure
1
d
esignedfor
t
husformin
g
aloguevolt
a
fromeach
o
d
onaDIN‐r
a
c
onnections
r
eachchan
n
n
el.
1.Signalco
n
usetogeth
e
g
twochann
e
a
geandacu
r
therand
a
ilorattach
e
toLVD3ar
e
n
el.Adjustm
e
n
ditionerL
V
LVDTSig
n
e
rwith
e
lsfor
r
rentloop. 
e
dbytwo
e
made
e
ntpotentio
V
D3.
n
alConditio
n
metersand
n
erLVD3
1
t
est


OperatingandInstallationinstructions
2
Functions
Figure2.
Eachchannelofthesignalconditionerincludesanoscillatorwithamplitudecontrol,supplying
thetransducerprimarycoilwithACvoltage.
Theamplitudecontrolfunctionsetstheoscillatoramplitudesothattheprimary
voltage,orthemeanvalueofthesecondaryvoltages,remainsconstantrelative
totheinternalreference.Usingfeedbackofthesecondarysignalsreducesinfluenceonthe
positionmeasurementfromtemperatureandfromcables.
Theinputsforthesecondarycoilshavehighimpedancetoavoidloadonthetrans‐ducer.After
phasedetection,thetwosignalsarecombinedtoabipolarvoltage
signalthatisfiltered,givingaDCvoltagesignalproportionaltothecoreposition
inthetransducer.
Gainforthepositionsignalisadjustedbyapotentiometerinoneofthreeranges,selectedby
switches.Zerooffsetforthesignalisalsoadjustedbyapotentiometer.
Thepositionsignalisacurrentloop(4to20mA)andamonopolarvoltage
(0to+10VDC)orabipolarvoltage(‐10to+10VDC).
LVD 3
4 - 20 mA
4
Demod.
Current
Output
Sec. 1
Osc.
U
Bal.
Gain high
mid
low
1
2
3
SW1
SW2
Sec. 2
I
Amplitude
Control
LVDT Signal Conditioner
Com.
Com.
Sec. 2
3
6
5
1
2
Sec. 1
Com.
Prim.
Prim.
10
9
I out
Com.
-10 - +10V
or 0 - +10V
4 - 20 mA
Voltage
Output
4
Demod.
Current
Output
Sec. 1
Osc.
U
Bal.
Gain high
mid
low
1
2
3
V out
SW1
SW2
Sec. 2
I
Amplitude
Control
Com. V out
Com.
Sec. 2
3
6
5
1
2
Sec. 1
Com.
Prim.
Prim.
10
9
7
8
Com.
I out
Com.
CHANNEL 2
CHANNEL 1
SEC.
PRIM.
SEC.
PRIM.
SW3
0 - 10V
-/+10V
-10 - +10V
or 0 - +10V
Voltage
Output
V out
V out
7
8
Com.
SW3
0 - 10V
-/+10V
Position transducer
type LVDT
Position transducer
type LVDT
24V
+
-
+15V
-15V
Com.
Com.
DC
DC
11
12
200 mA
slow
+15V
-15V
Com.
Com.
DC
DC
11
12
200 mA
slow
24V
+
-

Figure2.LVD3blockdiagram.

LVDTSignalConditionerLVD3
3
Technicaldata
Oscillatorforprimarycoil
Frequency2.5–3.2kHz
Frequencystab.±1%
Distortionmax.4%
Signal max.6VAC,150mA
Amplitudestab.±0.1%
Inputsforsecondarycoils
Inputvoltagemax.6.8V
Inputimpedancemin150kohm
Outputs
VoltageoutputisselectableasBipolarorMonopolar.
Bipolarvoltage±10V,Rload>6kohm
Monopolarvoltage0–10V,Rload>6kohm
Currentoutput4–20mA,Rload<500ohm
Linearity ±0.05%
Offsetadjust.range±2–±7%ofrange
Offsetdrift max.2mV
Gainranges low:2.1–5.8
(differentialACinputmid:5.2–15
tobipolarDCoutput) high:14–39
Gaindriftmax.0.1%
Filterbandwidth 125Hz(‐3dB)
Powersupply(perchannel)
Supplyvoltage 24VDC±20%
Fuse 200mA,slow
Continuouscurrent <120mA
Surgecurrent250mA
CEconformity
EMCindustrial,process
Temperaturerange
Operation0–+50ºC
Storage‐25–+85ºC
Mechanical
MountingrailDIN46277/3orDINEN50022(35mm)
Boxdimension75x100x110mm
Protection IP20
Testsockets 2mm


OperatingandInstallationinstructions
4


Figure3.Potentiometersandtestsocketsforbothchannelsare
accessibleatthefrontpanel.Allconnectionstoonechannel
aremadethroughasingleplug‐interminalblock
ononesideoftheLVD3module.
Com.
Prim.
Sec. 1
Sec. 2
Bal.
Gain
V out
LVD 3
Channel 1
V out
Gain
Sec. 1
Sec. 2
Com.
Bal.
Prim.
Channel 2
COM.
PRIM.
COM.
SEC. 1
COM.
SEC. 2
COM.
V OUT
COM.
I OUT
+
-
24V
1 2 3 4 5 6 7 8 9 10 11 12
CHANNEL 1
ARTNR.
S/N: 110 171
COM.
PRIM.
COM.
SEC. 1
COM.
SEC. 2
COM.
V OUT
COM.
I OUT
+
-
24V
1 2 3 4 5 6 7 8 9 10 11 12
CHANNEL 2

LVDTSignalConditionerLVD3
5
OPERATINGINSTRUCTIONS
General
Figure3.
TheLVD3modulefrontpanelhasadjustmentpotentiometersforgainandzerooffsetofboth
channels.Inadditionallimportantmeasuringpointsareaccessibleintestsocketsatthefront.
Tofullyexploitthemeasurementrangeofthetransducer,correctadjustment
ofthezerooffsetforthechannelisimportant.Thecorecentrepositionforadifferential
transformer(e.i.atypeLVDTtransducer)isanextremelyaccuratereferencewhichshould
thereforecoincidewiththecentreoftheoutputsignalrange.
AssumethatonechannelofLVD3issetforanoutputsignalof‐10to+10V.
Then,withcorrectadjustment,0Vwillcorrespondtothecorecentrepositionfor
theconnectedtransducer.Consequently,‐10and+10Vwillcorrespondtothelimits
ofthemeasurementrangefortheconnectedtransducer.

Potentiometers
Gain – Adjustmentofgainforthechannel.
Bal. – Adjustmentofzerooffsetforthechannel.
AdjustmentofgainandzerooffsetisthoroughlydescribedintheINSTALLATIONsection.

Testsockets
Figures2and3.
Com. – Measurementreference.
Prim. –Outputsignaltothetransducer.
Sec.1 –Inputsignalfromthetransducer.
Sec.2 –Inputsignalfromthetransducer.
Vout –Voltageoutput.
(Valuesofthetransducersignalsdependonfeedback,transducertypeandtransducercore
position.)

UseofthetestsocketsisthoroughlydescribedintheFAULTFINDINGsection.


OperatingandInstallationinstructions
6


30
7
35
75
100
110
5
60
85
Mounting holes,
2 x 4 mm dia. The snap lock for the
DIN rail can be opened
with a fine screw driver.

Figure4.MechanicaldimensionsforLVD3.

LVDTSignalConditionerLVD3
7
INSTALLATION
General
Figure4.
Themoduleisintendedformountingonstandard35mmDIN‐rails.
Duringinstallationvariousparametersandconfigurationsaresetby
switchesandpotentiometersonthecircuitboard.
Connections
Figure2.
24Vsupply
Connect+24Vtoterminal11and0V24toterminal12.
Transducers
Usescreenedcableswithtwistedpairs.Connecttheprimarycoiltoterminals
1and2.Connectonesecondarycoiltoterminals3and4andtheother
toterminals5and6.
Toreversethemeasuringdirectionforonetransducer,changeplacesfor
thesecondarycoilconnections.Seefigure2,terminals3/4and5/6.
Outputsignals
Twooutputsignalsareavailableforeachchannel:
onecurrentloopoutput,4–20mA,fromterminal10toterminal9.
onevoltageoutput,0–+10Vor‐10–+10V,atterminal8
with0Vreferenceatterminal7.
ThevoltageoutputcanalsobemeasuredattestsocketVout(referenceCom.).
Set‐upprocedure
General
Figure5.
Eachchannelhasaseparatecircuitboardwithtestsockets,potentiometersandswitchesfor
selectionoffeedbacktype,gainrangeandtypeofvoltageoutput.
Togiveaccesstotheswitches,themodulefrontpanelshouldberemoved.
ThentheswitchesSW1andSW3ontheouteredgeofthecircuitboardcanbereached.To
reachswitchSW2,pressthesidewallsoftheboxaparttorelease
thecircuitboard,andpullitout.
SwitchsettingsatdeliveryareshowninatableatAppendix1.

OperatingandInstallationinstructions
8
Feedbackselection
Figure5.
Twofeedbacktypesforamplitudecontroloftheoscillatorareavailable.Either‘PRIM.’:
feedbackoftheprimaryvoltagetothetransducer(defaultsetting),or‘SEC.’:feedbackof
themeanvalueofthetransducersecondaryvoltages.
SetswitchSW2onthecircuitboardaccordingly.
Certaintransducersaremanufacturedwithlinearization,whichmakesthemeanvalueofthe
secondaryvoltagesdependentonthecoreposition.Thesetransducersmustbeusedwith
feedbacktype‘PRIM.’.
Transducersforwhichthemeanvalueofthesecondaryvoltagesisindependent
ofthecoreposition,withinthelinearrange,canbeusedwithfeedbacktype‘SEC.’.Checkthat
theoscillatoroutputdoesn’texceed6VAC!
Feedbacktype‘SEC.’givesaconsiderablyreducedinfluenceonthemeasurementfrom
temperaturevariationsandcablelength.
Calibration
General
Thetwochannelsareidentical,sothecalibrationiscarriedoutinthesamewayforboth
channels.
Adjustingthezeropoint
Figure5.
Forapositiontransducer,typeLVDT,thecorecentrepositionisanaccurate
referencepoint.Itshouldcorrespondtothecentreoftheoutputsignalrange
(0Vforbipolarand+5Vformonopolarvoltage,12mAforcurrentloop).
Settingofthiszeroreferencepointshouldbeperformedinfoursteps:
STEP1:
SettheamplifiergaininmediumrangebytheswitchesSW1:
SW1,no.1andno.3toOFF,
SW1,no.2toON.
Thenadjustthetransducercoretoanapproximatecentreposition.
(ThiswillbringtheACvoltagebetweentestsocketsSec.1andSec.2
closeto0V.Ifnot,thetransducerconnectionisprobablynotcorrect;
oneofthesecondarycoilsmustbephasereversed.)
STEP2:
ConnecttestsocketSec.1toSec.2.
ThenusepotentiometerBal.toadjusttheoutputsignal
tothecentreofitsrange(0V,+5V,or12mA).
STEP3:
Adjustthemovingmachinecomponenttotherequiredcentreposition.
STEP4:
RemovetheconnectionSec.1toSec.2.
Thenadjustthetransducercoremechanically,withoutchangingthemachinepartposition,to
bringtheoutputsignaltothecentreofitsrange(0V,+5V,or12mA).
Fineadjustingofthezeroreferencepointmaybenecessaryafterchanging
thegainsetting.

LVDTSignalConditionerLVD3
9
Adjustingthegain
Figure5.
Thegainistobeadjustedsothatmaximumoutputsignalisobtainedwhen
themovingmachinepartisinitsmaximumposition.Themeasuringrangecanbereversed,
tomaketheoutputchangeinthecorrectdirection,byswitching
theconnectionsforthetransducersecondarycoils(terminals4and6).

FirstuseSW1toselectthemediumgainrange
(SW1,no.2settoON,SW1,no.1andno.3settoOFF).
Thensetthemovingmachinepartintherequiredmaximumposition.
ReadtheoutputsignalandusepotentiometerGaintoadjustit.
Turnclockwisetoincreasetheoutputsignal,turncounterclockwisetodecreaseit.

Ifasufficientlyhighoutputsignalcannotbeobtained,thehighgainrangemustbeselectedby
SW1(SW1,no.3settoON,SW1,no.2andno.1settoOFF).
Ifasufficientlylowoutputsignalcannotbeobtained,thelowgainrangemustbeselectedby
SW1(SW1,no.1settoON,SW1,no.2andno.3settoOFF).

IfthegainrangehasbeenchangedbySW1,STEP2under‘Adjustingthezeropoint’shouldbe
executedagain,andthentheconnectionSec.1toSec.2mustberemoved.Finally
potentiometerGaincanbeadjustedsothattherequiredoutputsignalisobtainedwiththe
movingmachinepartinmaximumposition.
13
2
SW1
ON
OFF
SW3
-/+10
0 - 10
SW2
SEC. PRIM.
Com.
Prim. Sec. 1 Sec. 2
Bal. Gain. V out
Fuse

Figure5.LocationofswitchesonaLVD3circuitboard.

OperatingandInstallationinstructions
10


LVDTSignalConditionerLVD3
11

Cable Cable
Demodulator Amplifier
Oscillator
Gain Bal.
24 V
Channel 1
Demodulator Amplifier
Oscillator
Power Supply
Gain Bal.
Channel 2
LVD 3
Output signals
Cable Cable
24 V
Position Transducer
type LVDT
Position Transducer
type LVDT
Power Supply
Output signals


Figure6.Systemforpositionmeasurement.

OperatingandInstallationinstructions
12
FAULTFINDING
General
Figure6.
Weshallconcentrateondescribingfaultfindinginameasurementsystem
includingthesignalconditionermodule.Faultfindingandrepairworkinside
themoduleshouldonlybecarriedoutbyThermoNobel.
Thetwochannelsareidenticalandthefaultfindingprocedureisequalforbothchannels.
Successfulpositionmeasurementrequiresthatallunitsinthesystemworkproperly:
transducer,cablesandsignalconditionermodule.
Withsimplemeansitispossibletodeterminewhetheraunitisoperatingornot.
Thesignalpathsofthesystemcanbemeasuredwiththepoweronoroff.

Transducers
Useamultimeter,settoresistancemeasurement,tocheckthatthetransducercoilresistances
correspondtothevaluesinthetransducerspecification.
Generallytheprimarycoilhasthelowestresistanceandthesecondarycoilsmutuallyhavethe
sameresistance.
Checkthetransducerattachmentandthatthecoreandcoreconnectingrodareproperly
fitted.

Transducercables
Figure2.
Theresistanceofthecablescanbemeasuredseparatelytocheckforopencircuitsorshort
circuits.Thecablescanalsobecheckedwiththetransducersconnected,
inwhichcasethedifferenceinimpedancemustbeinsignificantcomparedwithmeasurement
onthetransduceronly.


LVDTSignalConditionerLVD3
13
Signalconditionermodule
Figures2and5.
Firstchecktheconnectionsandthatallrelevantswitchsettingsontheboardhavebeendone.
Selectprimaryfeedback,(SW2inposition‘PRIM.’)tosimplifythefaultfinding.
Thencheckthemoduleinconjunctionwiththetransducer.
Powersupply
Checkthepowersupplytothemodule,measuringwithaDCvoltmeter:
+24VDCatterminal11,0V24atterminal12.
Observethatthemodulehasoneinternalfuseforeachchannel.
Outputfromoscillator
Checktheoutputsignalfromtheoscillatortothetransducerprimarycoil,measuringwithan
ACvoltmeter:
3.3–3.5VACatterminals1and2.
Ifthereisnovoltage,disconnectthetransducerandchecktheoutputagain.
Ifthereisstillnovoltage,(NOTE,SW2mustbesetforprimaryfeedback),it
indicatesthattheinternalfusemaybeblown.Inothercasesthereisafault
intheoscillator,andthecircuitboardmustbechanged.
Ifthefaultdisappeared,thetransducerandtransducercablemustbechecked
withrespectofshort‐circuits.
Iftheoscillatorfunctioniscorrectyoucanproceedandchecktheinputsignals
fromthetransducer.
Inputsignalsfromtransducer
InputsignalstoLVD3fromthetransducercanbecheckedatthetestsockets
Sec.1andSec.2.Firstensurethatthetransducerprimarycoilissuppliedfrom
theoscillator,measuringattestsocketsPrim.–Com.(3.3–3.5VAC).
ThenchecktheACvoltageatSec.1–Com.andSec.2–Com.respectively.
Checkthatthevoltagedecreasesforonecoilandincreasesfortheotherwhen
thetransducercorepositionischanged.
AlsocheckthattheACvoltagebetweenSec.1andSec.2isclosetozero
whenthetransducercoreisinthecentreposition.Ifnot,theconnectionsfor
oneofthesecondarycoilsmustbereversed.
Ifthischeckingwithprimaryfeedbackissatisfactory,faultsintheoscillator,transducerand
transducercablecanbeexcluded.

OperatingandInstallationinstructions
14
Iffeedbackofthesecondaryvoltageswillbeused,thisfeedbacktypefor
amplitudecontroloftheoscillatormustalsobechecked.
Changetosecondaryfeedback(SW2inposition‘SEC.’).
MeasuretheACvoltageat:
testsocketsSec.1–Com.
testsocketsSec.2–Com.
forafewdifferenttransducercorepositions.
Calculatethemeanvalueofeachpairofmeasuredvoltages.
ThesemeanvaluesshallbeequaltothevoltageattestsocketsPrim.–Com.,measuredearlier
withprimaryfeedbacksetting(3.3–3.5VAC).
TheactualvoltagePrim.–Com.mustbelessthan6VAC,orthetransformerratioofthe
transducerisnotsuitableforsecondaryfeedback.
Outputsignals
Disconnecttheoutputloadandcheckthatoutputsignalsareobtainedinresponseto
transducercoremovementsovertheentiremeasuringrangeasfollows:
Bipolaroutput:±10VDCattestsocketsVout–Com.
Monopolaroutput:0–+10VDCattestsocketsVout–Com.
Currentoutput:4–20mAfromterminal10toterminal9,usinganammeter
or
2–10VDCacrossa500ohmresistor,connectedtoterminals10and9.

Cableswithload
DisconnecttheoutputcablesfromLVD3andmeasuretheloadresistance,includingthe
cables,withamultimeter:
Loadforthecurrentoutputmustnotexceed500ohms
Loadforthevoltageoutputmustexceed6kohms.



LVDTSignalConditionerLVD3
15

13
2
SW1
ON
OFF
SW3
-/+10
0 - 10
SW2
SEC. PRIM.
Com.
Prim. Sec. 1 Sec. 2
Bal. Gain. V out
Fuse


ComponentsideofLVD3circuitboard.
EqualforChannel1andChannel2.