CMA ML42m User guide

PHSENSORML42M

USER’SGUIDE



CENTRE FOR MICROCOMPUTER APPLICATIONS

http://www.cma-science.nl

2|ML42mpHSensorUser’sGuide

Shortdescription

The pH sensor ML42m measures the degree of acidity/pH value of a solution in the range

from0to14pH.ThepHelectrodeisconnectedtothesensorboxbymeansofacoaxcable

andaBNCconnector.

The pH 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an

interfaceisnotsuppliedwiththesensor(sensorcablesaresuppliedwithinterfaces).

Sensor

specifications

The pH sensor ML42m is a digital sensor that converts the measured pH value to a digital

valuevia16‐bitanalog‐to‐digitalconversion.

Theresolutionofthesensoris±0.0002pH.

pHelectrode

ThepHelectrodeisagel‐filled glasselectrodebuilt inaplastictube

withanopeningatthe

bottom side. The pH electrode has been designed to function in a reliable and accurate

mannerundervariedconditions.TheruggedepoxybodyprotectsthepHsensingglassbulb.

Thegel‐filledreferenceelectrodeissealedanditneverneedstoberefilled.

The pH

electrode is supplied

inastoragebottlecontaining

a protective solution. When

it is not being used, it must

be kept in this storage

solution. During measure‐

mentstheelectrodemustbe

dipped in the solution for

about1‐cm.

The pH electrode can be

damaged beyond repair by improper use

 such as keeping the electrode in distilled water

storage,usageoveritstemperaturerangeandlongtimeexposuretostrongacid/base.

ThepHelectrodehasalimitedoperationallifeandcanbeorderedseparately.

PreparingthepHelectrodeforuse

Carefully remove the electrode from the bottle of storagesolution

and rinse the tip of the

electrode with distilled water. If air bubbles are seen in the pH bulb, gently shake the

electrodedownward,likeaclinicalthermometer,untilthebubblesdisappear.Theelectrode

isreadyformeasurement.

Maintenanceandstorage

Maintain the level of pH electrode storage solution, the pH

 sensitive membrane must be

keptwet.StoretheelectrodeinapH4buffer,towhichpotassiumchloride(KCl,10g/100ml)

hasbeenadded(pH‐4/KCl).

ML42mpHSensorUser’sGuide| 3



CAUTION:Neverstorethe electrodeindistilledwater.Usingorstoringtheelectrodeatvery

highorverylowtemperatures(near0°C)candamageitbeyondrepair.



Toprepareadditionalstoragesolution(pH‐4/KCl):

1. pH4.00buffer:add2.0mLof0.1MHClto1000mLof0.1potassiumhydrogenphthalate.

2. pH‐4/KClsolution:add10gofsolidpotassiumchloride(KCl)to100mLofpHsolution.

Cleaningoftheelectrode

A dirty but

 mechanically intact electrode can often be restored by one of the following

procedures,ingeneral:soaktheelectrodein0.1MHClfor15minutes.

 Deposit of proteins: soak the electrode in 0.1 M HCl to which 1% of Pepsin has been

added.

 Deposit of inorganic material: rinse

the electrode with a 0.1 M EDTA tetrasodium

solution.

 Depositofoilorgreasefilms:washtheelectrodeinamilddetergentorsolventknownto

attacktheparticularfilm(butnottheelectrodeitself!).

Aftercleaning,soaktheelectrodeinpH7bufferfor30minutes.Ifnoneof

theseprocedures

improveresponse,replacetheelectrode.

Donotusetheelectrodein:

 base solution (pH > 10) for longer than a few hours. This can affect the glass of the

electrode,

 hydrofluoricacidorinacidorbasesolutionwithaconcentrationgreaterthan1.0M,



solutionscontainingperchlorate,silver,orsulfideions.

The electrode can be used to measure the pH of sodium hydroxide solutions with a

concentration near 1.0 M, but should not be left in this concentration for periods of time

longerthan5minutes.

Whitecrustontheelectrode

The white crystals you

 might find on the electrode are formed by the Potassium Chloride

(KCl) from the storage solution. Carefully remove the electrode from the bottle of storage

solution,rinsetheelectrodewithdistilledwaterandproceedasusual.

Collectingdata

ThispH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.

Calibration

The pH sensor is supplied with a factory calibration and gives values in pH. The Coach 6

programallowsshiftingthepre‐defined

calibrationorcreatinganewthree‐pointcalibration

if needed. For routine measurements, one buffer suffices the calibration. For precise

calibrationoftheelectrodethreebuffersolutionsarerequired.Onebuffershouldbecloseto

4|ML42mpHSensorUser’sGuide

the desired measuring range. During calibration you need to

rinsetheelectrodewithdistilledwater.Theusercalibrationis

storedinnon‐volatileusersensormemory.

Suggestedexperiments

ThepHsensorcanbeusedforvariousexperimentssuchas:

 MeasurementsofpHofdifferentacidsandbases

 Acid‐base

titrationexperiments.

 MonitoringpHduringchemicalreactions.

 Investigationsofwaterqualityinstreamsandlakes.



TechnicalSpecifications



Sensorkind Digital:on‐sensordigitalconversion

(16‐bitsresolution,communicationviaI2C)

Measuringrange 0..14pH

Resolution ±0.0002pH

Uncertainty(accuracy) Typical±1.0%aftercalibrationat25°C

Temperaturerange 5°Cto80°C

(IfyouareusingthepHelectrodeatvarioustemperatures,

itiscertainlyneededtocalibratethesensorthroughthree

pointswithtemperaturecompensationbytheNernst

equationE=E

‐kT*pH)

Maximalsamplingrate 10Hz

Dimensions Sensorhousing:37x18x16mm

Connection 5‐pinsminijackplug

Warranty:

The pH sensor ML42m 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 a pply if the

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



Rev. 17/11/2011



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

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

CMA ML42m User guide

Related papers

Other documents