HD3910.1HD3910.2

[ GB ] Probes for soil moisture measurement

[ GB ][ GB ] Characteristics•Measurementofthesoilmoisturewith2electrodes(HD3910.1)or3electrodes(HD3910.2)forrestrictedvolumes

•Measurementofthesoiltemperature•RS485digitaloutputwithMODBUS-RTUprotocol•Accurateandstablemeasureovertime•DegreeofprotectionIP67•Minimalinvasivenessinthesoil•Easytoinstall

Application•Agriculture•Hydrology•Geology

DescriptionTheprobesHD3910.1 (twoelectrodes)andHD3910.2 (threeelectrodes)measurethesoilvolumetricwatercontent(VWC)byusingacapacitivemeasurementprinciplewhichallowsfastmeasurementsinthefieldandwithminimalinvasiveness.Thethree-electrodeprobe HD3910.2isparticularlysuitableforthemeasurementinsmallvolumes,forexampleforcultivationsinpots.Theprobesarefactory-calibratedanddonotrequireanyfurthercalibrationbytheenduser.Thecircuitboardisprotectedinsideahousingmadeofplasticmaterialandsealedwithepoxyresinwhichallowsachievingreliablemeasurementseveninharshenvi-ronmentalconditions.TheRS485digitaloutputwithMODBUS RTU protocolallowstheuseofevenverylong connection cables. It can be connected to the data loggers HD32MT.1 andHD32MT.3ortoanyotherdataloggerwithRS485MODBUSRTUinput.Theprobesareequippedwithafixedcable,5or10mstandard length,withopenwiresattheend.

Volumetric water contentThemoistsoiliscomposedofasolidpart(minerals),aliquidpart(generallywater)andagaseouspart(air,watervapor).TheVolumetricWater Content (VWC) is defined as the ratio between the volumeoccupiedbythewater(Vw)inacertainportionofthesoilandthetotalvolumeofthesoilportion(V):

VWC = VwV

Itcanalsobeexpressedasapercentage(%VWC)ofthewatervolumeinthetotalvolume.Thevolumetricwatercontentisaparameterusedinhydrologyforthestudyofthehydraulicpropertiesofthesoil,andinagriculturetodeterminetheneedtoirrigatecrops.

Technical specifi cations

Soil moistureMeasuringprinciple CapacitiveMeasuringrange 0…100%VWC(VolumetricWaterContent)Resolution 0.1%Accuracy(@23°C) ±3%between0and0.57m3/m³

(standardmineralsoilupto5mS/cm)Sensoroperatingtemperature -40…+60°CSoil temperatureSensor NTC10kΩ@25°CMeasuringrange -40…+60°CResolution 0.1°CAccuracy ±0.5°CLong-termstability 0.1°C/yearPower supply 5…30VdcConsumption 2mAaverage@12Vdc

(20mAapprox.@12Vdcduringthe100msmeasurementduration;ameasurementpersecondiscarriedout.)

Output RS485withMODBUSRTUprotocolMaterials Handle:thermoplasticmaterialandepoxyresin

Electrodes:epoxyglass,thickness2mmConnection Fixedcablewithopenwiresattheend,length5

or10mstandardProtection degree IP67Weight 150gapprox.(includingthe5mcable)

Fig. 1: dimensions (mm)

InstallationBymeansofanaccessory,performaholeintothesoildeepenoughtoaccommodatetheprobe.Neverusetheprobetomaketheholeinthesoil,inordertoavoidmecha-nicaldamagetotheprobeitself.Oncetheholewasdone,inserttheprobecompletelyintothesoilsothattheentirehandleiscoveredbytheground:thetemperaturesensorislocatedinsidethehandle,closetotheelectrodes;thereforeitisnecessarythatthehandleisimmersedinthesoilforacorrectdetectionofthetemperature.Aftertheintroductionoftheprobe,fillintheemptyspacesbetweenthesoilandtheprobewithsomesoilmadepowder.Toobtainaccuratemeasurements,thesoilshouldbeincontactwiththeelectrodesandtheprobehandle.

Probe 3910.1

Temperature sensorSoil level

Handle

Electrodes

Fig. 2: Installation

Theprobecanbeorientedinanydirection,butitisadvisabletoplaceitverticallyintotheground,sotonothindertheflowofwaterdownwardandtominimizetheinfluenceoftheprobeinthesoilbehavior.

Warnings:•Theportionofsoilinwhichtheprobeisinsertedmustbeuniform,withoutexces-siveairgaps,andnottoocompactasitwouldmaketheintroductionoftheprobedifficult.

•Payattentiontothepresenceofroots,stonesorotherobjectspresentinthesubsur-facethatmaycomebetweentheelectrodesandaffectthemeasure.

•Donotuseexcessiveforcewhenintroducingtheprobe,stoavoidirreparableda-magetotheelectrodes.

•Theprobemeasuresthewatercontentofthesoilvolumeimmediatelysurroundingtheelectrodes:positiontheprobesothattherearenoobjectsclosetotheprobe,suchasmetalpolesforexample,thatmayaffectthefieldofactionoftheprobeitself,.

•Indicatethepresenceoftheprobeduringthemaintenanceoperationsofthesoil(e.g.lawnmowing,ploughing,mechanizedharvesting,etc.).

• Inordertoremovetheprobefromthesoil,grabthehandleandpull itupwards.During the extraction, remove the probe vertically, by avoiding tilt that would damage the electrodes.

• Do not remove the probe by pulling the cable.

Connections

Wire color FunctionBlack NegativepowersupplyRed PositivepowersupplyWhite RS485A/-Green RS485B/+

Termination Termination PLC, data logger orconverter RS485/USB

or RS485/RS232 for PC

Power supply5…30 Vdc

Probe cable

Green

White

Black

Red

Other sensors with RS485 output

Fig. 3: Connections

Setting of RS485 communication parametersBeforeconnectingtheprobetotheRS485networkyoumustassignanaddressandsetthecommunicationparameters,ifdifferentfromthefactorypreset.The parameter setting is performed by connecting the probe to the PC by using aRS485/USBorRS485/RS232.Theprobemustbepoweredseparately. IfRS485/USBconverterisuseditisnecessarytoinstalltheappropriateUSBdriversinthePC.

Probe cable

RedPower supply

White

Green

Black

Fig. 4: connection to PC

Notes on the installation of unsigned USB drivers: beforeinstallingunsignedUSBdriversintoWindowsoperatingsystems7and8,itisnecessarytorestartthePCdisablingthedriversignaturerequest.Iftheoperatingsy-stemis64-bit,evenafterinstallation,itisnecessarytodisabletherequestofthedriversignatureeverytimethePCisrestarted

Procedure for setting the parameters1.Startwhiletheprobeisnotpowered.2.Startaserialcommunicationprogram,HyperTerminalforexample.SettheBaudRateto57600andsetthecommunicationparametersasfollows(theinstrumentappearsconnectedtoaCOMtypeport):

DataBits=8,Parity=None,StopBits=2 Intheprogram,setthenumberoftheCOMporttowhichyouconnecttheprobe.3.Switchtheprobeon.4.Waituntiltheprobetransmitsthe&character,thensend(within10secondsfromprobepoweron)thecommand@andpressEnter.

Note: iftheprobedoesnotreceivethe@commandwithin10secondsfrompo-weron,theRS485MODBUSmodeisautomaticallyactivated.Insuchacase,itisnecessarytoswitchoffandpowerontheprobeagain.

5.SendthecommandCAL USER ON. Note:theCALUSERONcommandisdisabledafteraninactivityof5minutes.6.SendthefollowingserialcommandstosettheRS485MODBUSparameters

Command Reply Description

CMAnnn &| SetaddressRS485tonnnRangingfrom1to247.Preseton1

CMBn &| ISetRS485BaudRate:n=0==>9600,n=1==>19200Preseton1==>19200

CMPn &| SetRS485transmissionmode(databits,parity,stopbits): n=0⇒8N1,n=1⇒8N2,n=2⇒8E1 n=3⇒8E2,n=4⇒8O1,n=5⇒8O2 Preseton2⇒8E1

CMWn &| SetreceivingmodeafterRS485transmission:n=0⇒ViolateprotocolandgoinRxmoderightafterTxn=1⇒Respectprotocolandwait3.5charactersafterTxPreseton1==>Respecttheprotocol

Probe 3910.2

1. It ispossible to check the settingsof theparametersby sending the followingcommands:

Command Reply Description

RMA Address ReadRS485address

RMB Baud Rate(0,1)

ReadRS485BaudRate:0⇒9600,1⇒19200

RMP Tx Mode(0,1,2,3,4,5)

ReadRS485transmissionmode:0⇒8N1,1⇒8N2,2⇒8E1,3⇒8E2,4⇒8O1,5⇒8O2

RMW Rx Mode(0,1)

ReadreceptionmodeafterRS485transmission:0⇒ViolatetheprotocolandgoinRxmoderightafterTx1⇒Respecttheprotocolandwait3.5charactersafterTx

Note:thecommandCALUSERONisnotrequiredforreadingthesettings.Operating mode TheprobeentersRS485MODBUSRTUmodeafter10secondsfrompoweron.Duringthefirst10secondsfrompoweron,theprobedoesnotrespondtoanyrequestoftheMODBUSmasterunit.After10seconds,itispossibletosendMODBUSrequeststotheprobe.Reading the measurementsInMODBUSmode,itispossibletoreadthemeasuredvaluesbyusingthefunctioncode04h(ReadInputRegisters).ThefollowingtableshowstheMODBUSInputRegistersavai-lable:

Registri MODBUS – Input RegistersRegister Number

Register Address

Datum Format

2 1 Soilmoisture%VWC(VolumetricWaterContent)[x10]

16-bitinteger

3 2 Apparentdielectricpermittivity[x10] 16-bitinteger4 3 Soiltemperaturein°C[x10] 16-bitinteger5 4 Soiltemperaturein°F[x10] 16-bitinteger

MaintenanceThe probe does not require any specialmaintenance.We recommend a periodiccleaningwithwater andnormal detergent of the electrodes in order to avoid theaccumulationofsubstancesthatmayalterthemeasures.

Ordering codesHD 3910.1.5: Two-electrode probe for the measure of the soil moisture. Digital

RS485outputwithMODBUSRTUprotocol.5mcable.HD 3910.1.10: Two-electrode probe for themeasure of the soilmoisture. Digital

RS485outputwithMODBUSRTUprotocol.10mcable.HD 3910.2.5: Three-electrodeprobeforthemeasureofthesoilmoistureinrestricted

volumes.DigitalRS485outputwithMODBUSRTUprotocol.5mcable.HD 3910.2.10: Three-electrodeprobe for themeasure of the soilmoisture in re-

strictedvolumes.DigitalRS485outputwithMODBUSRTUprotocol.10mcable.

0104.15

RoHS2002/95/EC

DeltaOhmsrl

ViaG.Marconi,5

35030CasellediSelvazzano(PD)-Italy

Tel.00390498977150r.a.

Fax0039049635596

e-mail:info@deltaohm.com

WebSite:www.deltaohm.com

Manufacture of portable, bench top and process scientific instrumentsCurrent and voltage loop transmitters and regulatorsTemperature - Humidity, Dew point - Pressure - CO, CO2

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CE CONFORMITY• Safety: EN61000-4-2, EN61010-1 Level 3• Electrostatic discharge: EN61000-4-2 Level 3• Electric fast transients: EN61000-4-4 Level 3, EN61000-4-5 Level 3• Voltage variations: EN61000-4-11• Electromagnetic interference susceptibility: IEC1000-4-3• Electromagnetic interference emission: EN55022 class B