CMA ML72m User guide

ORPSENSORML72M

USER’SGUIDE



CENTRE FOR MICROCOMPUTER APPLICATIONS

http://www.cma-science.nl

2|ML72mORPSensorUser’sGuide

Shortdescription

The ORP sensor ML72m measures the ability of a solution to act as an oxidizing or

reducing agent. ORP stands for oxidation‐reduction potential also known as Redox

Potential.

TheORPsensorconsistsofanORPelectrodeandanamplifier.TheORP(combination) 

electrode has two components: a measuring half cell

 comprising a platinum metal

immersed in the test solution in which the redox reaction is taking place, and a

reference half cell (a sealed, gel‐filled Ag/AgCl electrode) surrounded by a salt

solution. The measuring platinum electrode serves as an electron do nor or electron

acceptor depending upon the test solution

and the reference electrode is used to

supply a constant stable output for comparison. The ORP electrode measures the

redox potential – the voltage difference generated by the platinum measuring 

electrodeandthevoltageproducedbythereferenceelectrode‐intherangeof‐450

to 1100 mV. Readings  toward the positive

 region of this range indicate a strong

oxidizingagent,whilereadingstowardthenegativeregionindicateastrongreducing

agent.



The ORP electrode has been built into a long plastic tube with an opening at the

bottom side and is supplied with a storage bottle containing a protective solution.

WhentheORPelectrodeisnotbeingused,itmustbekeptinthestoragebottle.

Duringmeasurementstheelectrodemustbe

dippedinthesolutionforroughly1cm.

The electrode is connected to the amplifier by means of a coax cable and a BNC

connector.



TheORPsensorisanI2Cdigitalsensor,whichgivescalibratedvaluesofthemeasured

quantity. This sensor can only be connected to special interfaces that support I2C

digitalsensorsliketheCMAMoLabinterface.Thesensorcableneededtoconnectthe

sensortoMoLabisnotsuppliedwiththesensor,

itissuppliedwithMoLab.

Sensorspecifications

TheORPsensorML72mis a digitalsensorthat converts the measured ORP potential

toadigitalvaluevia16‐bitanalog‐to‐digitalconversion.Themaximalsamplingrateof

thesensoris15Hz.

Collectingdata

This ORP sensorworks only with specific interfaces.Thesensorwillbe automatically 

detected when connected to such an interface. For detailed information about

measurementswithsensorsconsulttheUserManualsoftheinterfaceandtheCoach

6software.

ML72mORPSensorUser’sGuide |3

Calibration

The ORP sensor is supplied with a factory calibration for redox potential in mV. The

Coach 6 programallowsshifting the pre‐defined  calibration orcreating anew three‐

point calibration if needed. The user calibration is stored in non‐volatile user sensor

memory.

InmostexperimentswiththeORPsensor

theprecisepotentialin mVisnotcritical.As

aresult,youdonothavetoperformanewcalibration,justusethecalibration stored

inthesensor.

If you are doing water quality testing or performing a chemistry experiment that

requiresaveryaccuratecalibration,youwill needto

obtaintwoorthreecommercial

ORPstandards.Usingthesestandards,performthecalibration:

 Forthefirstcalibrationpoint,rinsethetipoftheelectrodewithdistilledwater,and

placetheelectrodeintothefirststandard.Whenthevoltagereadingdisplayedby

thedata‐collectionprogramstabilizes,entertheORPvalue

(mV)ofthefirstORP

standard.Cleantheelectrodewithdistilledwaterandwipeitdry.

 Repeatthecalibrationforthesecondandthirdcalibrationpoint.

 Rinsetheelectrodewithdistilledwaterandplaceitintothesampletobe

measured.

Suggestedexperiments

Redoxreactionscontrolthe behaviorofmanychemicalconstituentsindrinkingwater,

wastewater and aquatic environments. The reactivity and solubility of critical

elementsinlivingsystemsarestronglydependentonredoxconditions.ORPvaluesare

usedmuchlikepHvaluestodeterminewaterquality.For exampleforswimmingpools

ata

normalpHvaluebetween7.2and7.6,theORPvaluemustbekeptabove700mV

tokillunwantedorganisms.Incontrast,inordertosupportlife,naturalwatersneeda 

much lower ORP value. Generally ORP values above 400 mV are harmful to aquatic

life.

The ORP sensor can

also be used for re dox titrations to determine the equivalence

pointinanoxidation‐reductionreaction.



4|ML72mORPSensorUser’sGuide



TechnicalSpecifications



Sensorkind Digital:16‐bitsresolution

(on‐sensordigitalconversion)

communicationviaI2C

Measuringrange ‐450mV..1100mV

Resolution 0.024mV

Maximumsampling

15Hz

Sensordimensions

Housing:67 x 19 x 19 mm

Connection 5‐pinsminijackplug



ORPElectrode

Type

Sealed,gel‐filled,epoxybody,Ag/AgClreference

Storagesolution

pH‐4/KClsolution(10gKClin100mLbufferpH‐4solution)

Temperaturerange

0‐60

C

Impedance

~20kΩat25

C

ORPelement

99%pureplatinumbandsealedonaglassstem

Connection

coaxialcablewithBNCconnector



Warranty:

The ORP sensor ML72m is warranted to be free from defects in materials and

workmanshipfor a periodof12monthsfromthedateofpurchaseprovidedthatithas

been used under normal laboratory conditions. This warranty does not apply if the

sensorhasbeendamagedbyaccidentormisuse.





Note:Thisproductistobeusedforeducationalpurposesonly.Itisnotappropriatefor

industrial,medical,research,orcommercialapplications.    

Rev. 10/06/2012

CMA ML72m User guide

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