GDS GDS-68XP User manual

GDS Corp
1245 Butler Road League City, TX 77573
409-927-2980 409-927-4180 (Fax) www.gdscorp.com
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Operation and Maintenance
Manual
GDS-68XP Process Monitor for Low O2Applications

GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 2
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CAUTION: FOR SAFETY REASONS THIS EQUIPMENT MUST BE OPERATED AND
SERVICED BY QUALIFIED PERSONNEL ONLY. READ AND UNDERSTAND
INSTRUCTION MANUAL COMPLETELY BEFORE OPERATING OR SERVICING.
ATTENTION: POUR DES RAISONS DE SÉCURITÉ, CET ÉQUIPEMENT DOIT
ÊTRE UTILISÉ, ENTRETENU ET RÉPARÉ UNIQUEMENT PAR UN PERSONNEL
QUALIFIÉ. ÉTUDIER LE MANUE D’INSTRUCTIONS EN ENTIER AVANT
D’UTILISER, D’ENTRETENIR OU DE RÉPARER L’ÉQUIPEMENT.
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REVISION HISTORY
Revision 3.0 6/5/13 Initial rewrite for version 3.0
Revision 3.1 11/1/13 Update for GASMAX CX
Revision 3.2 12/15/13 Update for v2.3 sequencer firmware
Revision 3.4 1/30/14 Update for v2.4x sequencer firmware
Revision 3.5 11/10/14 Errata, updated filter information
Copyright © 2014 GDS Corp. All Rights Reserved
P/N 1200-0732-05

GDS-68XP Operation & Maintenance Manual, Revision 3.5
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Page 3
CONTENTS
1SAFETYINFORMATION_______________________________________________8
2GENERALINFORMATION______________________________________________9
Introduction_________________________________________________________________9
ExplosionProofInstallation____________________________________________________9
IntrinsicallySafeInstallation____________________________________________________9
3SPECIFICATIONS____________________________________________________10
4OPERATION_______________________________________________________12
Overview__________________________________________________________________12
SampleDrawConfiguration___________________________________________________14
SensorConsiderations________________________________________________________14
5INSTALLATION_____________________________________________________15
SelectingaLocation__________________________________________________________15
Power&SignalConnections___________________________________________________16
On‐DemandSequenceInput___________________________________________________16
EthernetConnection_________________________________________________________16
RelayConnections(Optional)__________________________________________________17
MODBUSConnections(Optional)_______________________________________________17
ACHeater(Optional)_________________________________________________________19
PurgeAirInlet______________________________________________________________19
SampleInlet________________________________________________________________20
FilterDrain&FilterBypass____________________________________________________21
SampleExhaust_____________________________________________________________22
InstallationSummary:Do’sandDon’ts__________________________________________23

GDS-68XP Operation & Maintenance Manual, Revision 3.5
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6INITIALSETUP_____________________________________________________24
Overview__________________________________________________________________24
SequencerControlsandIndicators______________________________________________24
SEQUENCE_______________________________________________________________________24
Bypass__________________________________________________________________________25
Run____________________________________________________________________________25
L1andL2________________________________________________________________________25
GASMAXControlsandDIsplay_________________________________________________26
RAWSENSOR____________________________________________________________________26
PPMOUTPUT____________________________________________________________________26
DUALDISPLAY____________________________________________________________________26
GDS‐68XPSTARTUPPROCEDURE_______________________________________________27
7CALIBRATION______________________________________________________28
CalibrationOverview_________________________________________________________28
CalibrationProcedure(CALPORTSAMPLE)_______________________________________29
CalibrationProcedure(INLETPORTSAMPLE)_____________________________________30
CalibrationProcedure(STREAMSAMPLE)________________________________________31
8OPERATIONandMAINTENANCE_______________________________________32
NormalOperation___________________________________________________________32
ColdWeatherOperation______________________________________________________32
NormalMaintenance________________________________________________________32
FaultandoverrangeConditions________________________________________________33
PowerUp_______________________________________________________________________33
InputOverrangeFAULT____________________________________________________________33
SensorRecoveryFAULT____________________________________________________________33
PeakAlgorithmfault_______________________________________________________________33
SampleorPurgeAirFlowfault_______________________________________________________33
Calibrationfault__________________________________________________________________33
SensorFailfault__________________________________________________________________33

GDS-68XP Operation & Maintenance Manual, Revision 3.5
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SensorReplacement_________________________________________________________34
9USERMENUS______________________________________________________35
AlarmOUTPUTSMenu_______________________________________________________36
ChannelSettingsMenu_______________________________________________________37
CommSettingsMenu________________________________________________________39
SystemSettingsMenu________________________________________________________40
DiagnosticsMenu___________________________________________________________41
10MODBUSREGISTERS______________________________________________42
ListofGDS‐68XPMODBUSvariables____________________________________________42
11TROUBLESHOOTINGGUIDELINES____________________________________50
FaultIndicationonOUTPUTChannel(CH2)_______________________________________50
FaultIndicationonrawSensorChannel(CH1)____________________________________50
SensorFailsCalibration_______________________________________________________50
GDS‐68XPandReceivingDeviceDisplayedValuesDon’tMatch______________________50
ControllerMODBUSDataIncorrect_____________________________________________51
ControllerShowingMODBUSCOMMERROR_____________________________________51
GDS‐68XPDisplayBlank______________________________________________________51
12SPAREPARTS____________________________________________________52
13DRAWINGSANDDIMENSIONS______________________________________57
14WIRINGDIAGRAMS_______________________________________________58
15GASMAXCXGDS‐68XPFACTORYDEFAULTSETUP_______________________59
16SEQUENCERSETTINGS(DIPSWITCHVERSIONS)_________________________65
17KNOWNERRATA__________________________________________________66
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GDS-68XP Operation & Maintenance Manual, Revision 3.5
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TABLEOFFIGURES
FIGURE3‐1:TOXICSENSORCHARACTERISTICS............................................................................................11
FIGURE3‐2:SEQUENCETIMING...................................................................................................................11
FIGURE3‐3:RECOMMENDEDMINIMUMSEQUENCETIMES.......................................................................11
FIGURE4‐1:GDS‐68XPFLOWDIAGRAM(PRESSURE)..................................................................................12
FIGURE4‐2:GDS‐68XPSAMPLETIMING......................................................................................................13
FIGURE4‐3:GDS‐68XPMAXIMUMTIMINGVALUES....................................................................................13
FIGURE4‐4:GDS‐68XPFLOWDIAGRAM(SAMPLEDRAW)..........................................................................14
FIGURE5‐1:GDS‐68XP(HIGHPRESSURE,STANDARDFILTER).....................................................................15
FIGURE5‐2:GDS‐68XPPOWERANDSIGNALWIRING..................................................................................16
FIGURE5‐3:RELAY/MODBUSCONNECTIONS.............................................................................................17
FIGURE5‐4:MODBUSWIRINGJUNCTIONBOX............................................................................................18
FIGURE5‐5:200WACHEATERWIRING........................................................................................................19
FIGURE5‐6:INLETTUBINGRECOMMENDATIONS.......................................................................................20
FIGURE5‐7:FILTERDRAIN&EXHAUSTTUBINGRECOMMENDATIONS.......................................................21
FIGURE5‐8:GDS‐68XPEXHAUSTTUBING....................................................................................................22
FIGURE6‐1:GDS‐68XPUSERINTERFACE......................................................................................................24
FIGURE6‐2:SEQUENCETIMING...................................................................................................................25
FIGURE6‐3:L1/L2INDICATOROPERATION................................................................................................25
FIGURE6‐4:GDS‐68XPGASMAXDISPLAYSEQUENCE..................................................................................26
FIGURE7‐1:CALIBRATIONPROCEDURE(CALPORT)....................................................................................29
FIGURE7‐2:CALIBRATIONPROCEDURE(INLETPORT).................................................................................30
FIGURE7‐3:CALIBRATIONPROCEDURE(SAMPLESTREAM)........................................................................31
FIGURE8‐1:FAULTCONDITIONS..................................................................................................................33
FIGURE9‐1:MAINMENUTREE....................................................................................................................35
FIGURE9‐2:ALARMOUTPUTSMENUTREE.................................................................................................36
FIGURE9‐3:CHANNELSETTINGSMENUTREE(1)........................................................................................37
FIGURE9‐4:CHANNELSETTINGSMENUTREE(2)........................................................................................38
FIGURE9‐5:COMMSETTINGSMENU..........................................................................................................39
FIGURE9‐6:SYSTEMSETTINGSMENUTREE................................................................................................40
FIGURE9‐7:DIAGNOSTICSMENUTREE.......................................................................................................41
FIGURE12‐1:GDS‐68XPSAMPLEDRAWCOALESCINGFILTER(SPAREPARTS).............................................52
FIGURE12‐2:GDS‐68XPLOWPRESSURECOALESCINGFILTER(SPAREPARTS)............................................53
FIGURE12‐3:GDS‐68XPHIGHPRESSURECOALESCINGFILTER(SPAREPARTS)...........................................54

GDS-68XP Operation & Maintenance Manual, Revision 3.5
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FIGURE12‐4:GDS‐68XPHIGHPRESSUREBYPASSFILTER(SPAREPARTS)....................................................55
FIGURE12‐5:GDS‐68XPSENSORHEADEXPLODEDVIEW............................................................................56
FIGURE13‐1:GDS‐68XPDIMENSIONS(NEMA4XENCLOSURE)...................................................................57
FIGURE14‐1:GDS‐68XPWIRINGDIAGRAM.................................................................................................58
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GDS-68XP Operation & Maintenance Manual, Revision 3.5
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1SAFETYINFORMATION
Important–ReadBeforeInstallation
UsersshouldhaveadetailedunderstandingofGDS‐68XPoperatingandmaintenanceinstructions.Use
theGDS‐68XPonlyasspecifiedinthismanualordetectionofgasesandtheresultingprotectionprovided
maybeimpaired.ReadthefollowingWARNINGSpriortouse.
WARNINGS
TheGDS‐68XPprocessmonitordescribedinthismanualmustbeinstalled,operatedand
maintainedinaccordancewithinformationcontainedherein.Installationinanyhazardousarea
mustcomplywithallapplicablerestrictions,requirementsandguidelinesforsaidhazardous
areas.Itistheendusercustomer’sfinaldecisiontoensurethattheGDS‐68XPissuitableforthe
intendeduse.
TheGDS‐68XPisdesignedandconstructedtomeasurethelevelofcertaingasesinbackgrounds
thatcontainlowamountsoffreeoxygen.Accuracyinatmospherescontainingsteamorinert
gasescannotbeguaranteed.
Donotpaintenclosure,transmitterorsensorassembly.
DonotoperatetheGDS‐68XPifitsenclosureisdamagedorcrackedorhasmissingcomponents.
Makesurethecover,internalPCB’sandfieldwiringaresecurelyinplacebeforeapplyingpower.
DonotexposetheGDS‐68XPtoelectricalshockorcontinuousseveremechanicalshock.Protect
theGDS‐68XPfromdrippingliquidsandhighpowersprays.
Calibratewithknowntargetgasatstart‐upandcheckonaregularschedule,atleastevery90
days.Morefrequentinspectionsareencouragedtospotproblemssuchasdirt,oil,paint,grease
orotherforeignmaterialsinthesampletubingorinthesensorhead.
Periodicallytestforcorrectoperationofthesystem’salarmeventsbyexposingthesample
extractionpointtoacalibrationgasconcentrationabovetheHighAlarmsetpoint.
Useonlyforapplicationsdescribedwithinthismanual.
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GDS-68XP Operation & Maintenance Manual, Revision 3.5
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2GENERALINFORMATION
INTRODUCTION
TheGDS‐68XPprovidesasafeandreliablewaytomeasurethelevelofhydrogensulfide,mercaptan,THT
andothergasesinaprocessstreamthatcontainslowlevelsofoxygen.TheGDS‐68XPusesaprogrammed
sequencertoalternativelyapplysampleandpurgeairtoahighlysensitiveandreliableelectrochemical
sensor.Applyingpurgeairperiodicallyrefreshesthesensor’schemistry,significantlyextendsthelifeof
thesensorandreducesthetotalamountofsamplegas
releasedintotheatmosphere.
TheGDS‐68XPcanbeconfiguredtodrawsamplesfrom
non‐pressurized(ambient)sourcesortoacceptpositive
pressuresamples,from+5psigto+1500psig.Multiple
filteroptionsareavailableandtheunitfeaturesalow‐flow
warningswitchandlonglifebrushlessDCpumpforsample
andpurgeair.
TheGDS‐68XPfeaturesthenewdual‐channelGASMAXCX
networkedgasmonitor.Inadditiontoanewhighvisibility
colordisplay,theGASMAXCXincludesanEthernetportwithbuilt‐inMODBUS/TCPinterfaceandweb
serverforcompleteintegrationintousernetworks.GDSCorpsoftwarecanbeusedtoremotelymonitor
thestatusandperformanceofGDS‐68XPsystemsifanetworkconnectionisavailable.
EXPLOSIONPROOFINSTALLATION
TheGDS‐68XPisdesignedforuseinClass1Division1hazardousareas.Installationintheseareasshould
followbestindustrystandardpracticesandallappropriateelectricalcodes.Generally,thesecodesrequire
rigidmetalconduit,pouredsealsandotherinstallationelementsnecessarytoensuresafety.For
maximumprotectionagainstRFinterferenceorelectricalsurge,theGDS‐68XPenclosureand
interconnectingconduitmustbeproperlygrounded.
INTRINSICALLYSAFEINSTALLATION
TheGDS‐68XPisnotdesignedorcertifiedforuseasanIntrinsicallySafedevice.
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3SPECIFICATIONS
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ModelGDS‐68XPProcessMonitorforLowOxygenApplications
PowerInput24VDC±5%at<12watts
DisplayHighresolutioncolorLCDwithengineeringunits,bargraphand30‐minutetrend
SensorTypesElectrochemicalsensorsfortoxicgases
InletPressure
Requirements
Sampledraw:Ambientto+5inchesofwatercolumn
Lowpressure/noregulator:+5incheswatercolumnto+25psig(±10%max)
Highpressure/standardfilter:+10psigto+1500psig
Highpressure/combinationfilter:+10psigto+1500psig
DrawDistanceDemonstratedupto100feetof¼”ODtubing
Accuracy+/‐5%offullscale(typical)
Standard
Output
Three‐wire4‐20mAcurrentsourceoutputswithfaultandoverrangeindication.
Maximumloopresistanceis750ohmswithstandard24VDCsupply.
EthernetRJ‐45withbuilt‐inMODBUS/TCPinterfaceandwebserver
OptionalRelay/MODBUSinterfacewith3x5ASPDTprogrammablealarmrelays.
Temperature
(operating)
0°Cto+50°Cstandard(noenclosure)
Note:Ambienttemperaturebelow0°Cmaykeeppurgeairpumpfromstarting
‐20°Cto+50°CwithNEMA4Xenclosureandoptional200WACheater.Heater
thermostatissetto50°Fandisnotuser‐adjustable.
Temperature
(inert)
‐20°Cto+55°C
Incoldweather,GDSCorprecommendsturningontheACheater(ifinstalled)for
severalhoursbeforeapplyingDCpower
MemoryOn‐boardnon‐volatilememoryretainsallusersettings
MaterialsInstrumenthousings:Aluminum
Tubing&fittings316stainlesssteel
DimensionsPaintedsteelplate:21”x21”x8”,
NEMA4xnon‐metallicenclosure,24”x24”x8”
ApprovalsGASMAXCXGasMonitorCSACertifiedClassI,Div1&2GroupsB,C,D.
SequencerenclosureCSAcertifiedforuseinClassIDiv1areas.
FlamearrestorsULcertifiedforuseinClass1Div1areas.
WarrantyTwoyearsonelectronics



GDS-68XP Operation & Maintenance Manual, Revision 3.5

Page 11

TypeTargetGas RangePartNumberTempRangeWarm‐Up
15HydrogenSulfide0‐10ppmto
0‐5000ppm10‐9815‐Rxxxx0°Cto+50°C2to4hours
30Mercaptan(TBM)
0‐15ppm
0‐50mg/m3
0‐3.00lbs/mmcf
10‐9830‐R0015
10‐9830‐R0050
10‐9830‐R0003
0°Cto+40°C4to8hours
31THT0‐15ppm
0‐3.00lbs/mmcf
10‐9831‐R0015
10‐9831‐R00030°Cto+40°C12to24hours
40Odorants0‐15ppm
0‐3.00lbs/mmcf
10‐9840‐R0015
10‐9840‐R00030°Cto+50°C2to4hours
41Spotleak0‐15ppm
0‐3.00lbs/mmcf
10‐9841‐R0015
10‐9841‐R00030°Cto+50°C2to4hours
Figure 3-1: Toxic Sensor Characteristics

SEQUENCE
Switch Sequence
Time Purge / Hold Time Total Cycle Time
(Approximate)
0On-Demand Sequence 1 hour
1 12-15 min 40 min 1 hour
2 12-15 min 105 min 2 hours
3 12-15 min 165 min 3 hours
4 12-15 min 225 min 4 hours
5 12-15 min 285 min 5 hours
6 12-15 min 345 min 6 hours
7 12-15 min 465 min 8 hours
Figure 3-2: Sequence Timing

RECOMMENDEDMINIMUMSAMPLESEQUENCETIMES
GASTYPEMINIMUM COMMENTS
15HYDROGENSULFIDE,LOWRANGE(<50PPM)1HOURFORMAXIMUMSENSORLIFE,USELONGEST
POSSIBLESEQUENCE
15HYDROGENSULFIDE(>500PPM)2HOURSFORMAXIMUMSENSORLIFE,USELONGEST
POSSIBLESEQUENCE
31TETRAHYDROTHIOPHENE,0‐50MG/M32HOURSTWOHOURSISREQUIREDFORCOMPLETE
SENSORRECOVERYFROMMETHANE
30MERCAPTAN,0‐50MG/M3OR0‐3LB/MCF4HOURSFOURHOURSISREQUIREDFORCOMPLETE
SENSORRECOVERYFROMMETHANE
40,
41
GENERALODORANTS,INCLUDINGSPOTLEAK2HOURSTWOHOURSISREQUIREDFORCOMPLETE
SENSORRECOVERYFROMMETHANE
Figure 3-3: Recommended Minimum Sequence Times


GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 12
4OPERATION
OVERVIEW
TheGDS‐68XPuseslowcost,reliableelectrochemicalsensorstodetecthydrogensulfide,mercaptan,THT
andothertracegasesinprocessstreamsthatcontainlittleornooxygen.Aselectrochemicalsensors
requireoxygentooperate,theGDS‐68XPalternativelyexposesthesensortotheprocessflowandthen
purgesthesensorwithambientairtomaintainthesensorinasensitive,oxygenatedstate.




Figure 4-1: GDS-68XP Flow Diagram (Pressure)

Atthebeginningofeachsequence,theGDS‐68XPperformsConditionstheSensorbyallowingasmall
sampleofgastoenterthesensorflowcell,followedbyafixed5minutedelay.The68XPthenenters
SampleChargeduringwhichsamplegasflowsintothesensorflowcellfortwominutes,oruntilsensor
outputexceeds25%ofscale.Oncesamplepre‐chargeiscomplete,thesequencerentersReadmode
wherethesequencerprocessorattemptstoidentifyastablepeakvalue.Oncethesamplevalueis
PurgeAir
Pump
Flow
Switch
CalGasInlet
Sample
Inlet
FlowMeter
SampleOutlet
Sensor
FlowCell
Run/Cal
Valve
3‐Way
Valve
Pressure
Regulator
PurgeAir
Inlet
Filter
RAWSENSOR
(Ch1)
PPMOUTPU
T
(Ch2)

GDS-68XP Operation & Maintenance Manual, Revision 3.5

Page 13
identifiedandstored,theGDS‐68XPentersRecoverymodewherepurgeairflowsintothesampleflow
cell.Oncethesensoroutputdropsbelow10%ofscale,theGDS‐68XPtransfersthestoredreadingtothe
4‐20mAandMODBUSoutput.Intheeventthatanoverrange,lossofflow,peak‐findalgorithmfault,non‐
return‐to‐zerofault,sensorfaultorcalibrationfaultoccurredduringthesequence,aspecificfault
indicationvaluewillbeoutputinplaceofthemeasuredvalue.Finally,theGDS‐68XPentersPurge/Hold
mode,duringwhichpurgeairisperiodicallypassedacrossthesensortoprepareitforthenextsequence.
ThelengthofthePurge/HoldtimeisdeterminedbytheSEQUENCEswitchsetting.




Figure 4-2: GDS-68XP Sample Timing

GDS‐68XPSequenceTiming
Condition
Sensor
Fixed
Delay
Sample
Charge
Sample
Read
Sensor
Recovery
Purge/Hold

Valveopens,
sampleflows
tosensor
Purgeair
appliedto
sensor
Valveopens,
sampleflows
tosensor
Sequencerfinds
andstoresmax
gasreading;
valvecloses
Purgeairapplied
tosensoruntil
output<10%of
scale
Purgeairapplied
tosensor
(intermittent)
Fixed5‐10
seconds
Fixed5
minutes
Twominutes
orvalue>25%
Min:2seconds
Max:5minutes
Min:1second
Max:10minutes
Determinedby
sequenceswitch
Figure 4-3: GDS-68XP Maximum Timing Values

Value or Fault indication transferred to Output
Condition
Sensor
Recovery
Purge/Hold
“RAWSENSOR”
“
OUTPUT
”
Delay
Charge
NewCycleRead

GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 14
SAMPLEDRAWCONFIGURATION
Inadditiontolowandhighpositivepressureversions,theGDS‐68XPcanbeconfiguredtodrawasample
fromambientpressuresources.Inthisconfigurationthepumpoperatescontinuouslytopullfromboth
purgeairandsamplesources(SeeFig.4‐4).



Figure 4-4: GDS-68XP Flow Diagram (Sample Draw)
SENSORCONSIDERATIONS
TheGDS‐68XPsupportselectrochemicalsensorsforhydrogensulfide,THTandmercaptan.Eachsensor
containsafixedamountofchemicalelectrolytethatreactswiththetargetgastocreatefreeelectrons
thatareamplifiedandmeasured.Oncetheelectrolyteisdepleted,sensoroutputwilldiminishandthe
sensormustbereplaced.
IMPORTANT:TOXICSENSORSARESUBJECTTOACCELERATEDDETERIORATIONIFPOWERISNOTAPPLIED
WITHIN3MONTHSOFSHIPMENTFROMGDSCORP.
PurgeAir
Pump
Flow
Switch
CalGasInlet
Sample
Inlet
FlowMeter
SampleOutlet
Sensor
FlowCell
Run/Cal
Valve
3‐Way
Valve
PurgeAir
Inlet
Filter

GDS-68XP Operation & Maintenance Manual, Revision 3.5

Page 15
5INSTALLATION
SELECTINGALOCATION
LocatetheGDS‐68XPascloseaspracticaltothesourceofthesamplegastominimizelatencyandensure
thatfreshsampleisavailableforeachsequence.TheGDS‐68XPplateand/orenclosurefeaturemounting
holesthatcanbeusedtosecurelyattachthemonitortoabulkheadorwall.Makesurethereissufficient
clearancebelowandtotheleftsideoftheGDS‐68XPtoallowroomforpower&signalcables,purgeair,
sample,filterbypass(ifinstalled),filterdrainandsampleexhausttubing.
Iftheunitisinstalledoutsideorwhereinsectsordustmaybepresent,besurethatthesuppliedpurgeair
filterisinplaceandthatacoverisplacedovertheCalGasInletport.
AlwaysmounttheGDS‐68XPinaverticalpositiontoensureproperoperationofflowswitchandfilter
drains.Thenon‐metallicenclosureoptionisstronglyrecommendedifunitistobeinstalledoutsideorin
areaswherehighorlowtemperatureextremesmayoccur.
NOTE:TEMPERATURESBELOW0°CMAYKEEPTHEPURGEAIRPUMPFROMSTARTING.
Alwaysuserecommendedconduitandpouredsealsforsignalandpowerwiringinstallationinhazardous
areas.Consultlocalcodesandregulationswhereappropriate.




Figure 5-1: GDS-68XP (High Pressure, Standard Filter)
PurgeAir
Inlet
Sample
Inlet
Power&Signal
Input
FilterDrain Sam
p
leExhaust
Re
g
ulator
FlowMeter
ACHeater
GASMAX
Se
q
uencer
Sensor
Sensor
Flow
Cell

GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 16
POWER&SIGNALCONNECTIONS
Toaccessthepowerandsignalwiring,removethecoverfromthe
explosionproofenclosure.Connectasourceof+24VDC,±10%power
towiringterminalsJ1‐1(+24V)andJ1‐3(GND).The4‐20mA(source)
outputisavailableatJ1‐2(SeeFig.5‐2).
ON‐DEMANDSEQUENCEINPUT
Ifthe“on‐demand’sequencermodeisselectedtheGDS‐68XPwillenteraholdmodeuntilanexternal
contactclosurebetweenJ6‐1andJ6‐2occurs.ThiscausestheGDS‐68XPtoperformasinglesample
sequence.Uponcompletion,theDONEoutputwillbepulledlowtosignaltheremotecontrollerthatthe
sequenceiscomplete.






Figure 5-2: GDS-68XP Power and Signal Wiring
ETHERNETCONNECTION
TheGASMAXCXgasmonitorincludesastandardRJ‐45EthernetconnectiononthemainI/Oboard.Both
fixedIPandDHCP‐baseddynamicIPaddressingissupported.TheGASMAXCXsupportsafullrangeof
MODBUS/TCPaccessibleregister(seeChapter10)aswellasabuilt‐inwebserverwithdatadisplayand
gasdetectorconfigurationpage.
J1
–
1:+24VDCPowerInput
J1–2:4‐20mAAnalogOut
J1–3:Power/SignalCommon
RecommendedDCWireGauge
<100ft#18GA
100to500ft#16GA
500to1000ft#14GA
J6
–
1:START:GroundtoCommontoinitiatesequence
J6–2:Common
J6–3:DONE:OpenCollectorOutput,pulledlowwhensequencecomplete
AccesstooptionalAlarmRelays,
MODBUSserialportsandEthernetis
via¾”NPTfittingonrightsideof

GDS-68XP Operation & Maintenance Manual, Revision 3.5

Page 17
RELAYCONNECTIONS(OPTIONAL)
TheoptionalGASMAXCXRelay/dualMODBUSRTUslaveinterfaceisconnected“piggyback”totheback
oftheGASMAXCXDisplayAssemblyandsuppliesthreelevelalarmrelays,aFAULTrelayanddualRS‐485
ModbusRTUserialports.


Figure 5-3: RELAY / MODBUS Connections

RelaysK1,K2andK3provideacontactclosureiftheAlarm1(“K1”)orAlarm2(“K2”)orAlarm3(“K3”)
limitsareexceeded.Alarmscanbeprogrammedtotriggeraboveorbelowacertainvalue,workasnormal
or‘failsafe’andcanbemadetolatchifdesired.RelayK3indicatesaFAULTconditioninthesensor,
microprocessororflowsystem.
RemoteAlarmResetcanbeusedtoacknowledgeanAlarm2relaycontactclosure.Wiringfromany
remotepushbuttontoTB3shouldbeshieldedandprotectedfromnoisespikestopreventfalseAlarm
Resetcommands.
WARNING:RELAYCONTACTSARERATEDFORRESISTIVELOADSONLY!INDUCTIVELOADSMAYCAUSE
ARCINGWHICHSHORTENSLIFEANDMAYINTERFEREWITHSENSORDATA.
MODBUSCONNECTIONS(OPTIONAL)
ThedualoptionalGDS‐68XPMODBUSRTUinterfaceallowsremotecontrollersorPLCstomonitormost
aspectsofoperation,includingreal‐timedata,rangeandalarmsetpointsandalarmandfaultstatusbits.
TheGDS‐68XPinterfacesupports9600BaudRS‐485differentialsignalingonly.
AccesstoeachMODBUSRS‐485interfaceisviaTB2ontheoptionalRelay/MODBUSboardmountedon
thebackoftheGASMAXCXdisplaymodule(SeeFig.5‐3).Separateinputandoutputterminalsfor
MODBUS“A”and“B”signalsareavailable.Acenterterminaltotieincomingandoutgoingshield
connectionsisalsoprovided.
2
3
4
1
TB1
5
B
S
A
A
B
TB2
RelayWiring:
1Fault1NC
2Fault1Common
3Fault1NO
4Relay3NC
5Relay3Common
6Relay3NO
7Relay2NC
8Relay2Common
9Relay2NO
10 Relay1NC
11 Relay1Common
12 Rela
y
1NO
MODBUSinterface
RemoteAlarmAcknowledge
ModbusWiring:
1ModbusA
2ModbusB
3ShieldTiePoint
4ModbusA
5ModbusB

GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 18
MODBUSsystemarchitecturerequiresthatthedevicesinanyMODBUSloopbeconnectedinadaisy‐
chainlayout.Thisminimizessignalreflectionsandimprovessignalnoisemargin.AMODBUSTermination
JumperinstallsaloadresistoracrosstheMODBUSsignallinesandshouldonlybesetto“A”(ON)atthe
lastdeviceinthestring(SeeFig.5‐3).
CableselectionforMODBUSsystemsisimportantforbothsignalintegrityandpowerdistribution.
MODBUS/RS‐485transmissionsuselow‐voltagedifferentialsignalingtoachievereasonabledatarates
oververylongdistances,upto4000feetwithoutarepeater.
ForMODBUSdatasignals,GDSCorprecommends20GAto
24GAtwistedshieldedcable.Daisy‐chainpowerdistribution
mayrequirelargergaugewiresinceitiscriticalthatthe
supplyvoltagefortheGDS‐68XPatthefarendofthestring
notfallbelow22VDCduringpower‐up.
NotethatwhiletheGDS‐68XPhastwosetsofwiring
terminalsforMODBUS“A”and“B”signals,daisy‐chainpower
wiringrequiresthattwowiresbeinstalledinthe“+24”and
“GND”terminalsontheGDS‐68XPI/OPowerSupplyboard.
Thiscanbedifficultifwiresizesarelargerthan#18GA.For
thesereasons,ifMODBUSisrequiredGDSCorprecommends
theadditionoftheMODBUSWiringJunctionBox(seeFig.5‐
7).Thisoptionminimizestheneedtoaccesswiringinsidethe
GDS‐68XP,providesindividualwirelandingpointsfor
incomingandoutgoingMODBUSandpowerwiringand
shields,andmakesiteasytotemporarilydisconnecttheGDS‐68XP
powerorMODBUSconnectionswithoutaffectinganyotherMODBUS
device.


+24 GND A 
+24 GND A 
PWRto
MODBUSto
+24
GND
“
A
”
“B”
+2
4
GND
“
A
”
“B”
Figure 5-4: MODBUS Wiring
Junction Box

GDS-68XP Operation & Maintenance Manual, Revision 3.5

Page 19
ACHEATER(OPTIONAL)
The200wattAC‐poweredheaterisrecommendedforoutdoorapplicationswhereambienttemperatures
mayfallbelowfreezingforextendedperiodsoftime.Theheaterisavailableineither110VACor230VAC
models.Accesstotheheaterwiringisviaaseparate¾”NPTfittingonthebottomoftheheaterjunction
box.NotethatallhighvoltageACwiringmustbekeptseparatefromlowervoltageDCandsignallines.



Figure 5-5: 200W AC Heater Wiring

LocalcodesandgoodwiringpracticerequireanACshutoffswitchwithinsightoftheheaterassemblyfor
maintenanceandtesting.IMPORTANT:Keepallelectricalfittingstightwhilecircuitsarealive.
PURGEAIRINLET
Purgeairshouldbedrawnfromasourceofambientairthatiscleanandfreeofsignificantlevelsof
hydrogensulfideorsimilartoxicgas.GDSCorprecommendsplacingthePurgeAirinletsomedistance
fromtheGDS‐68XP,inalocationthatisfreefrombackgroundgasandprotectedfromheavyrains,water
sprayandsnoworice.Includedwiththeunitisa¼”screenfittingthatmustbeplacedovertheopenend
ofthepurgeairinlettokeepdust,dirt,waterdropletsandinsectsfromenteringthetubingandbeing
drawnintothepurgeairpump.
ACHOT
Accesstoheaterwiringvia¾”NPTfittingonbottom
ofjunctionbox(enclosurecutoutnotprovided)
HeaterElement
FixedThermostat(ONbelow50°F/10°C)
ACNEUTRAL
ACGND
Thermostat
HeaterElement
Black
Green
Red/White

GDS-68XP Operation & Maintenance Manual, Revision 3.5
Page 20
SAMPLEINLET
ThelengthoftimeittakesgastoflowfromthesamplesourcetotheGDS‐68XPinletshouldnotexceed30
secondstoensurethat“fresh”sampleisavailableatthebeginningofeachmeasurementcycle.For¼”OD
stainlesssteeltubingandsampleflowratesofapproximately0.5litersperminute,themaximumlength
shouldbenomorethan60feet(~20m).Smallerdiametertubingwillallowlongerrunsbutmaybe
subjecttocloggingifthesamplecontainsparticulateormoisture.Largerdiametertubingshouldbe
avoidedduetotheinternalvolumeofentrainedgas.


Figure 5-6: Inlet Tubing Recommendations
IntheeventthattheGDS‐68XPmustbemountedatagreaterdistancefromthesamplepickuppoint,the
combinationcoalescing/bypassfilterisrecommended.Thisfilterincludesabypassportandbypassvalve
thatcanbeopenedslightlytoenableacontinuousflowofsamplefromthepickuppointtothefilter
input,ensuringthatfreshsampleisalwaysavailable.
IMPORTANT:WHENCONFIGUREDFORSAMPLEDRAW,THEGDS‐68XPSAMPLEPUMPISCAPABLEOF
PULLINGUPTO7.0PSIVACUUM,ENOUGHTOLIFTWATEROVER15FEET.CARESHOULDBETAKENNOT
TOSUBMERGETHESAMPLEPICKUPPOINTINLIQUID.INJESTEDLIQUIDISNOTCOVEREDUNDER
WARRANTY.
Ifaunitthathasbeenconfiguredforsampledrawisconnectedtoasamplesourcewithpressurehigher
thanambient,anadditionallow‐pressureregulatororflowrestrictiondeviceshouldbeinstalledinthe
sampleinletlinebeforetheGDS‐68XP.Thiswillallowthesampleflowtobeadjustedtomatchthepurge
airflow.
InletDelayCalculation
For¼”ODstainlesssteeltubing,
allow5secondsdelayforevery
10feetofsampleline.
Max60Feet
With¼”ODTubing
MountGDS‐68XP
abovesample
pointifpossible