TECHNICAL GUIDE - IC Controls · 2018-03-22 · references are the calomel electrode and the...

TECHNICAL GUIDE

pH SENSOR

um-600-sensor-r6

617 High Pressure Ball Valve Retractable

615 Pure Water pH Sensor

607 Ball Valve Retractable Cartridge pH Sensor

614 True-Union Sensor

642 pH Sensor

CONTENTS IC Controls

CONTENTSum-600-sensor-r6

CONTENTS.........................................................................................................................2pH MEASUREMENT.........................................................................................................3

WHAT IS pH?.................................................................................................................3pH Measurement Techniques..........................................................................................3pH Sensing Electrode......................................................................................................4The Reference Electrode.................................................................................................6pH Concerns In Industry.................................................................................................8

INSTALLATION..............................................................................................................15Selecting the Location...................................................................................................15Analyzer Location.........................................................................................................15pH Sensor Mounting.....................................................................................................15Sensor Wiring................................................................................................................19Instrument Shop Tests...................................................................................................20Preparation for Use........................................................................................................21

pH CALIBRATION...........................................................................................................22Selecting a pH Buffer....................................................................................................22Electrode Life................................................................................................................23Standardizing Single-Buffer Calibration...................................................................24Calibrating Two-Buffer Calibration..........................................................................25Grab Sample At Process Calibration.........................................................................26

INSERTING/REMOVING pH SENSORS.......................................................................28Preparation for Use........................................................................................................28Inserting pH Sensors.....................................................................................................28pH Sensor Removal.......................................................................................................30Removal 605-21 & 606-21 BV Sensor.........................................................................31

SENSOR MAINTENANCE..............................................................................................32Sensor Storage...............................................................................................................32Monthly Maintenance...................................................................................................32Yearly Maintenance......................................................................................................32Sensor Cleaning............................................................................................................32Mechanical Cleaning of Sensor.....................................................................................33

pH SENSOR TROUBLESHOOTING..............................................................................35Troubleshooting Tips for pH.........................................................................................36

GLOSSARY......................................................................................................................38DRAWINGS......................................................................................................................39

D5160327: Generic pH Sensor Wiring Diagram..........................................................39D4850015: pH Interface................................................................................................40

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IC Controls pH MEASUREMENT

pH MEASUREMENT

WHAT IS pH?

pH is a short form for the Power (p) ofHydrogen (H). pH is defined as thenegative log of the hydrogen ion activity,aH+ or the effective hydrogen ionconcentration.

Mathematical Definition

pH=log101

aH +1=−log10 aH+1

(Theoretical)

pH=log101

[H +1]=−log10[H

+1] (Practical)

Descriptive Definition

pH is a unit of measure which describesthe degree of acidity or alkalinity of asolution. Acidity is defined as the

concentration of hydrogen ions [H+] insolution and alkalinity as the concentrationof hydroxyl ions [OH-] in solution. Theactual theoretical definition of pH is -log10aH+. However, since the activitycoefficient (a) for hydrogen (H+) is 1, thepractical definition for pH can then bedefined as -log10[H+]. Refer to table 1 for achart showing the relationship between pHand the hydrogen ion concentration.

pH Measurement Techniques

There are two ways of measuring pH. Thefirst is a Colorimetric Method which usescolor indicators to indicate the pH of thesample. There are limitations to thismeasurement technique; for instance,visual measurement by an operator issubject to variation. As well, thistechnique is done by grab sample which isnot suitable for continuous on-line

measurement. A more effectiveway to measure pH in anindustrial setting is via thepotentiometric method of pHanalysis. The potentiometricmethod allows continuous on-linemeasurement and is not subject tooperator bias. Potentiometricanalysis consists of four parts;

1) sample

2) pH sensing electrode

3) reference electrode

4) signal amplifier/readout

When properly combined, theresult is accurate, representativepH readings.

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pH Hydrogen Ion (H+) Moles per Liter Hydroxyl Ion (OH-) Moles per Liter

0 (100) 1 0.00000000000001 (10-14)

1 (10-1) 0.1 0.0000000000001 (10-13)

2 (10-2) 0.01 0.000000000001 (10-12)

3 (10-3) 0.001 0.00000000001 (10-11)

4 (10-4) 0.0001 0.0000000001 (10-10)

5 (10-5) 0.00001 0.000000001 (10-9)

6 (10-6) 0.000001 0.00000001 (10-8)

7 (10-7) 0.0000001 0.0000001 (10-7)

8 (10-8) 0.00000001 0.000001 (10-6)

9 (10-9) 0.000000001 0.00001 (10-5)

10 (10-10) 0.0000000001 0.0001 (10-4)

11 (10-11) 0.000000000001 0.001 (10-3)

12 (10-12) 0.0000000000001 0.01 (10-2)

13 (10-13) 0.00000000000001 0.1 (10-1)

14 (10-14) 0.000000000000001 1 (100)

Table 1: Relationship between pH and hydrogen ion concentration


pH MEASUREMENT IC Controls

pH Sensing Electrode

The pH sensing electrode acts as one halfof a battery whose potential varies with thehydrogen ion concentration in solution.The standard glass electrode is commonlyused in industrial applications because ofits ruggedness and versatility. There areother solid state electrodes such as theantimony electrode which is a sensingelement made of antimony hydroxide andis used in applications such as highfluoride where glass is dissolved.

The Glass Electrode

Since the glass electrode is still theindustry standard for sensing electrodes, itwill be the only sensing electrodediscussed. The glass electrode generallyconsists of four major components;

1) glass membrane

2) internal buffer solution

3) reference wire

4) glass stem

How Glass Electrodes Work

The glass electrode is primarily composedof alkali silicates which are comprised ofsodium, potassium, lithium, silicate,oxygen and hydrogen. All of thesecomponents are combined to form ahydrogen ion specific sensing glass; theamount of each constituent in the glassdetermining its pH sensing properties.

When the glass is put into solution, itundergoes a chemical reaction which formsof a leached layer. The leached layer is thearea at the surface of the glass where anion exchange reaction occurs. In thissurface layer, hydrogen ions migrate in andreplace other positively charged ions suchas sodium or potassium. This causes asilica-oxygen-hydrogen bond to be set upwhich is essential for sensing hydrogen ionin solution.

The pH glass electrode actually works on atwo reference electrode basis; a referenceinside the glass and a reference that is incontact with the externals of the glass. pHmeasurement requires measurement of thepotential difference in the pH electrodesystem. The formation of a leached layeractually occurs on both sides of the glassmembrane. The difference in potentialbetween the two layers is called the phaseboundary potential and is the potentialdifference that gives the pH signal.

In the pH glass there must also be a chargetransport mechanism so that a millivoltpotential will be seen. In between the twoleached layers there remains a glassmembrane layer that does not undergo theion exchange that occurs at the surface. Inthis membrane layer, potassium andsodium, major constituents of the glass, actas the charge carriers.

For best results, a symmetrical cell is set upon both sides of the glass membrane. To


Illustration 1: Glass pH electrode


set up the symmetrical cell, the internal fillsolution in the glass and the reference fillsolution are similar in their makeup. Thesymmetry is important so that thetemperature curves for the two solutionsare as close as possible and minimize thetemperature effect. For symmetrypurposes, the internal buffer is made ofpotassium chloride (KCl) solution which isthe same as the reference solution.

Styles of Glass Electrodes

The basic premise behind glass electrodesis to have the reference and the hydrogenion sensitive glass membrane in contactwith the solution being monitored. Theglass membrane itself is not limited to anyconfiguration or shape; its onlyrequirement is contact with the solution.Therefore, different styles of glasselectrodes have evolved to maximize pHsensing ability and extend longevity insome of the more harsh applications.Refer to illustration 2 for examples ofvarious glass styles.

Temperature Effect on Glass

As the charge transfer is one of the keyfactors in determining pH, the conductivityof the internal layer of the glass is a factorin the responsiveness of the electrode. The

more conductive the glass is, the quickerthe transfer of potential difference acrossthe membrane. Thicker, ruggedized stylesof glass are slower to respond in ambientconditions than general purpose electrodesbecause it takes longer to transfer thecharge and set up the difference betweenthe leached layer potentials.

The conductivity of the glass, which is thereciprocal of resistance, is highlytemperature dependent, as seen in thefollowing equation; where k is theconductivity and A and B are constants:

−log k=A+ BT

From this equation, it is evident that as thetemperature increases the conductivity ofthe glass also increases. This explains whythick glass, which is somewhat sluggish atambient temperatures, will be veryresponsive when the temperature of thesample is increased. Illustration 3 is agraph that shows this relationship betweentemperature and the conductivity of theglass for a standard glass membrane.

Because of the temperature effect on theimpedance of the glass, a thinner glasswith a low impedance is used in ambientconditions and a thicker more rugged glass


Illustration 3: Temperature vs. pH glass resistance

Illustration 2: A) Dome B) Spherical C) Flat



with a higher initial impedance is used forhigh temperature applications.

Therefore, when selecting a glass electrodefor industrial pH systems, a number ofdifferent factors must be considered tomaximize response and longevity of theprobe in specific applications.

The Reference Electrode

The reference electrode acts as the otherhalf of the battery in the pH electrode. Thedifference in potential between the twosides of the pH glass measures the varyingpotential difference in the solutions due topH. Where the reference is constant, itgives the glass a reference point to use forthe glass electrode to distinguish that pHrelates to the process pH potentials.

As mentioned in the glass section, the bestresults for an electrode occur when the twosides are symmetrical. Thus, a referencecell is normally comprised of a silver (Ag)wire with the tip of the wire covered insilver chloride (AgCl). This Ag/AgCl wireis submersed in a saturated KCl solutionwhich is separated from the process by aporous junction. A diagram of a typicalcombination electrode with an Ag/AgClreference can be seen in illustration 4.

Like the glass electrode, there are alsodifferent types of reference electrodes thatcan be utilized in any given pHmeasurement. The two commonreferences are the calomel electrode andthe silver/silver chloride reference. Thecalomel electrode is not used in industrialapplications for two reasons. First, theelectrode tends to breakdown when thetemperature exceeds 80 °C or 175 °F. Aswell, the calomel electrode is partiallycomprised of mercury which is known tobe a health hazard thus making it less user

friendly than the Ag/AgCl reference.

The Ag/AgCl reference has a number ofadvantages for use in the industrial pHmarket. First, the temperature stability ofthis reference is good in applicationsranging up to 105 °C (220 °F). However,when stabilizers are added to the reference,accurate pH measurements can be taken totemperatures in excess of 125 °C (260 °F).With the stability of this reference and therelative ease of manufacture into acombination electrode, the Ag/AgClreference has become IC Controls'standard.

Reference Junction Impact

The silver/silver chloride reference has aporous junction between the KCl referencesolution and the process. This porousjunction acts as a barrier to keep thereference internals and the process fromreadily mixing and contaminating thereference which would render the referenceuseless.

Like the glass membrane, the junction cancause a noticeable potential difference inthe electrode. The difference in themagnitude of this potential is small incomparison to the glass but significant


Illustration 4: Combo electrode with Ag/AgCl reference


enough that choosing the proper junctioncan have an effect on the pH measurement.In considering which junction is used foran electrode, the chemical compatibility ofthe reference junction material with theprocess must also be considered.

Ceramic Junctions

In the industrial pH electrode there arebasically three styles of reference junctionsthat can be selected; ceramic, wood orporous plastic, depending on the processapplication. The first is the ceramicjunction which is very useful in ultra highaccuracy types of pH measurements due toits low junction potential. However, thereare some limitations with using thisjunction. The junction usually has verylittle surface area in contact with theprocess making it prone to clogging,especially in dirty or oily industrialapplications. As well, because of the verybrittle nature of ceramic, it is less shockresistant in applications where theelectrode comes in contact with smallrocks or pieces of debris on a regular basis.

For these reasons, the ceramic junction isprimarily used in the laboratory for grabsample purposes where high accuracy isrequired and the electrode will not besubject to the rigors of the process.

Wood Junctions

Another type of junction that can be usedwith the pH electrode is the wood junction.Wood, by nature, allows good transport ofliquid through its fiber and resists coatingfrom most substances. These two featuresmake the wood junction exceptional for

use in applications where coating from theprocess can occur. IC Controls' woodjunctions are normally manufactured witha larger surface area allowing for bettercontact with the process which is essentialin the dirtier applications that try to clogthe reference junction. The limitation ofwood occurs in high temperature and highpH environments.

Porous Plastic

For high temperature and high pHapplications, a porous plastic junction isused because it is chemically resistant andis not affected by temperature in thereadable temperature range of pH. Likewood, IC Controls' porous plastics aremanufactured with large surface areas sothat good solution contact is maintained. Ifan application is running over 50 °C(122 ° F) or above pH 8 continuously, aporous plastic junction will provide bestresults.




pH Concerns In Industry

Industrial pH applications exhibit anumber of different problems that arecommon and cause difficulties when tryingto measure pH. Below is a list of some ofthe most common pH measurementdilemmas and how to approach them toobtain optimal results.

Slope and Offset

The slope and offset are measures of probeefficiency and how close to theoreticallyperfect the probe is.

When a calibration is performed, the firststep is to use pH 7 buffer to calculate themV offset of the electrode fromtheoretically perfect 0 mV. A larger mVoffset is farther from a theoretically perfectelectrode. pH 7 buffer is used because itsimulates 0 mV thus making it the beststandard to calculate the offset from this0 mV reference point.

The next step in the calibration is to use asecond buffer, usually pH 4 or pH 10buffer; either of these buffers gives a largeenough mV differential that a good slopecan be calculated. When calculating theslope of the electrode a good separationbetween the buffers is needed so that anaccurate span between two points iscalculated. As well, when choosing whichbuffers to use in calibration, it is best toselect buffers that fall on both sides of thenormal operating pH. By using these twobuffers, the slope calculation willencompass the normal pH, thus giving themost accurate pH measurement. At 25 °C(77 °F), the slope is 59.16 mV per pH unitand the slope is measured as a percentageof this millivoltage. When performing thetwo point calibration, a percent value willbe given in microprocessor based pH

analyzers. The closer the slope is to 100%,the greater the efficiency and thus theperformance of the electrode.

Heat Effect on Slope

At 25 °C the slope of a 100% efficientprobe is 59.16 mV per pH unit with 0 mVstarting at pH 7. However, as thetemperature changes, so does the mV perpH unit as seen in illustration 5. In fact,the slope changes 0.1984 mV/°C. Thisrelationship is important in determining pHbecause if it is not used, the reading couldbe off by a significant amount.

For example, pH is being monitored in aprocess at pH 4 and 60 °C. The outputfrom the probe will be 198 mV accordingto the temperature to mV relationship. Ifthe analyzer does not use temperaturecompensation, it will see 198 mV andassume this reading is taken at 25 °C. At25 °C, 198 mV is calculated by the pHmeter to have a pH value of 3.64 which is athird of a pH unit lower than 4.0 pH.

Hence, it is vital to ensure temperaturecompensation is used and workingproperly in conjunction with the pH probeso that accurate pH readings are given bythe analyzer.


Illustration 5: Temperature vs. mV/pH unit


Caustic Ion Error

Another problem with pH electrodesoccurs at the high end of the pH scalewhen the concentration of hydrogen ions islow. In fact, high pH causes two problems.First, there is a high concentration ofhydroxide (OH-) ions coupled withextremely low hydrogen ions which willdehydrate the glass making it very sluggishin responding to pH changes. Secondly,and more importantly, a caustic (sodium)ion error will occur if the proper glass isnot used. As the pH value increases, theconcentration of hydrogen ion decreases.At the same time, the concentration ofsodium ion will increase. Sodium is veryclose to hydrogen in its chemical structureand, as a result, when the concentration ofhydrogen ion decreases the glass will startto recognize sodium as hydrogen giving afalse, low pH reading. By using high pHglass, the sodium ion error will be negatedas seen in illustration 6. Illustration 6graphically depicts the significant effectusing the proper glass can have on theaccuracy of a pH reading. Another benefitof high pH glass is its resistance to causticetching. Thus, using high pH glass willresult in improved performance as well asincreased sensor longevity.

Coating of the Glass

Various applications contain constituentsthat will coat the glass, such as calciumcarbonate which is present in systemswhere lime addition is used for effluentneutralization. Coating of the glass resultsin poor contact between the glass itself andthe process. Good contact by the electrodeis essential for accurate speedy response inthe process. Thus, to keep the glass cleanand responsive, there are a couple ofprocedures that can be used to help.

The first is to insert the electrode with theflutes at 75 degrees to flow, as indicated inillustration 7. By inserting the probe atthis angle, a vortex will be created aroundthe glass. The vortex will increase thevelocity of the process around the glassand reference which will hasten electroderesponse time and also keep the referencecleaner. Also, by turning the flutes to75 degrees, the process does not directlyhit the glass which will slow down thecoating action.

When the probe shows evidence ofcoating, a good cleaning procedure shouldbe used to restore the electrode back to100%. In the past, a hydrochloric acidsolution was used to remove scale from thetip of the electrode. Although this hasbeen somewhat effective, a gentle scaleremover will better clean the electrode. Ifthe pH response becomes sluggish and the


Illustration 6: High pH effect

Illustration 7: Electrode flute angles



slope of the probe starts to get too low, anelectrode renew solution can be used. Theelectrode renew solution will skim off amicro-layer of the coated glass, thusexposing a new glass surface which willexhibit better pH response.

Ground Loops

One of the more difficult problems toanalyze in a pH loop is a ground loopwhich does not necessarily exhibit anyvisual signs. Unlike scaling or evencaustic ion error, which is specificallylooked for at high pH values, a groundloop can occur at any pH under manydifferent conditions. Fortunately, there arecertain indicators that point to a groundloop problem.

First of all, it is important to know whatcauses a ground loop. A ground loopoccurs when an external charge is appliedto the pH system. When analyzing for aground loop, look for a pH offset in theprocess pH reading compared with a grabsample pH reading taken in a beaker justafter the electrode has just been calibrated.

As an example, a ground loop can occur ifan electrode is inserted into a pipe that iscarrying a charge which is then transferredby a short to the pH probe, or, in a chargedprocess, the pH reference cell can act like aground wire and current will flow throughit to any ground.

To alleviate a ground loop problem, anisolated reference input plus a ground wireor a solution ground is used to bleed offthe residual charge keeping the mV seenby the analyzer isolated to the potentialproduced by the pH reading itself.

Reference Contamination

Various processes contain a number ofdifferent constituents that can contaminate

the reference electrode - some constituentsmigrate into the reference and attack theAg/AgCl reference wire causing the wireto deteriorate over time. The referenceoffset is a gage of the reference electrode'slevel of deterioration. As the offset from0 mV increases, the reference is becomingmore contaminated. Within an offset of1.3 pH units, the electrode is still deemedto be adequate for use. Between 1.3 pHand 4 pH units, the electrode may still bewithin a usable range but has deterioratedsignificantly. When the offset reaches4 pH units or 240 mV, the reference hasbeen contaminated to the point where itcan no longer be relied upon for use in theprocess.

There are two major contaminants in theindustrial market, sulfide (S2-) and cyanide(CN-). Sulfide is commonly found in Kraftpulp and paper mills. All of the differentliquors analyzed in Kraft processes have ahigh sulfide content, therefore, the pulpstock will have a significant amount ofsulfide as well. Cyanide, on the otherhand, is primarily found in metalrefineries. Cyanide is commonly used as aprecipitate for metal separation in flotationcells. Thus, contamination of the referenceis an issue for both pH and ORP cellswhich are used in these processes.

To combat reference wire contamination,double junction and/or plasticizedreferences are used to slow down themigration of the sulfide or cyanide to thereference wire. Illustration 8 is a diagramof a single junction and a double junctionreference for comparison purposes.

The second junction is used to increase thepath length of the contaminants to thereference wire. The longer the migrationpath, the longer it will take to reach thereference wire thus extending the life of



the reference.

The second junction also acts as a barrierwhich will increase the impedance of themigrating ions, again extending referencelife. The other contamination deterrent isthe plasticized reference solution. Theplasticized reference is effective because itimpedes ion migration through a solid asopposed to a liquid. The more solid thereference solution the longer it will take forcontaminants to pass through thusprotecting the Ag/AgCl wire.

For applications that contain sulfide orcyanide, a double junction plasticizedreference will extend the life of the pH orORP probe.

Chemical Compatibility with Glass

An industrial pH stream usually has anumber of different chemicals present,some of which are not compatible with pHglass. One of these chemicals has alreadybeen mentioned in the Caustic Ion Errorsection which specifically addresses theproblem of hydroxide etching of the glasswhich will cause sluggish response.

Another chemical that causes problems ishydrofluoric acid (HF), which willeventually etch the glass membrane awayso there is no sensing glass left. To helpwith longevity of the electrode, thickerglasses are used so that it will take longer

to erode the sensing membrane. Be carefulof the relationship between temperatureand resistance of the glass; the thicker theglass the higher the resistance. Although athicker glass is better for HF applications,the normal operating temperature of theprocess must be taken into consideration,as mentioned in the Temperature Effect onGlass section, so that a compromisebetween longevity of the probe andresponse time is established. Testing ofvarious glass has shown that certain typesof glass resist fluoride attack better and areapplied to these applications.

Another chemical that should be taken intoconsideration is ferric chloride which isused in sewage systems as a complexingagent. Ferric chloride will attack the glasselectrode at the active pH sensing sitesrendering those sites inactive. Inactive pHsensing sites on the glass will result insluggish response to pH changes in theprocess. To contend with this problem,place the electrode in electrode renewsolution on a regular basis to skim off amicro-layer of inactive glass leavingbehind a fresh layer of glass for improvedpH response.


Illustration 8: Single junction vs. double junction



Sand Blasting Due to Slurry

Mining applications typically contain a lotof grit moving at a high velocity. Whengrit hits the glass sensing electrode, it has a"sand blasting" effect causing the glass tobecome pitted. This decreases theresponse of the electrode and wears theglass away. To help keep the glass intact,the probe should be turned so the flutes areat 75 degrees to the flow (refer toillustration 7). By inserting the probe atthis angle, a vortex will be created aroundthe glass. The vortex will increase thevelocity of the process around the glassand reference which will quicken electroderesponse time and keep the referencecleaner by using the abrasive nature of theslurry. By turning the flutes to 75 degrees,the process does not directly hit the glass.Keeping the glass out of the direct path ofthe sandblasting slurry will lengthenelectrode life.

Clogging of Electrode Tip

One of the major concerns in pulpapplications is clogging of the electrodetip. Pulp fibers can get caught in the areasurrounding the glass which clogs theelectrode. The reference and glass nolonger have contact with the process andthus proper pH measurements cannot betaken. There are two different electrodemodifications to help alleviate the cloggingproblem; one is by way of a flat style glassand the other is via a pulp modified tip.

With flat glass, the surface of the glass isparallel to the flow so the glass does notcome in contact with the solution as wellas a dome type of glass. The mosteffective way to design the probe is to usethe dome glass with a body configurationthat will not clog, while at the same time,protect the tip from the shearing action ofdense pulp stock. To accommodate all ofthese, a pulp modified tip, shown inillustration 9, was developed to ensurebetter contact with solution whileprotecting the tip from clogging andshearing action of the stock.

High Purity pH

Due to the lack of conductive ions in highpurity water, a number of interferencesoccur which show up as a drifting andspiked measurement, often far from thecorrect value. Without ions providing aconductive short circuit, the pH electrodecoupled to a modern ultra high impedancepreamp, acts as a high gain, high efficiencyantenna. Escaping chloride ions from thereference cell tend to partly short the highresistance system allowing the pHelectrode to establish a pH output. Whenchanges in sample flow occur, the rate atwhich these ions are swept away is upset,causing a compensating adjustment in thepH electrode. This effect is oftendescribed as sweeping away of the "ioncloud." A related effect is the junctionpotential at the reference junction which isalso affected by the number of ions and therate of sweeping away. As sample flowincreases, the actual conductivity producedby the ion drops due to fewer ions left stillin the area of the junction. The junction,like a thermocouple, puts out amillivoltage relative to the two dissimilarconductors it is composed of. This, ofcourse, changes if one of the conductors is


Illustration 9: Flat glass tip vs. pulp modified tip


changing.

A high purity pH electrode takes intoaccount all of these effects. A stainlesssteel flow cell is used for shieldingtogether with a total surround shield. Ionscarcity is compensated for by driving thecell with the analyzer power to produce anelectron rich environment. Sample flow isreduced to a low, constant figure and thereference junction is modified to provide amore gradual change in the conductivitylevel and thereby increases potentialstability. A large reservoir of KCl issupplied to provide the necessary ions andalso isolate the normal AgCl componentfrom the high purity water. Otherwise,silver with low solubility precipitates outto plug the junction and cause prematurefailure. IC Controls offers a pure water pHsensor, model 615, specially designed forlow conductivity samples.

Sluggish Response

When looking at the performance of anelectrode one of the criteria is the speed ofresponse. Thus, when the electrode is slowto respond to pH changes in the system, itis a concern. Therefore, it is important toaddress some of the different factors thatcan cause sluggish electrode performance.

Several different causes that effectelectrode performance have already beendiscussed in this article; coating of theglass, sand blasting due to slurry, causticion error, and the factors affecting theresistance of the glass. Yet, besides simple“old age” there is one other reason forsluggish response that is important.

Sluggish response is likely to occur whenan electrode is taken out of storage due tohydrolysis of the electrode membrane. Theelectrode is stored in salt water whenshipped, which is not hydrogen ion rich as

is best suited for the glass. To revive theelectrode, immerse it in a beaker of 4 pHbuffer until the reading gets relativelyclose to pH 4. Rinse off the electrode andplace it in pH 7 buffer until the readinggets relatively close to pH 7. Keepalternating between pH 4 and pH 7 bufferuntil the response time is normal.

Comparison with Lab Results

When analyzing the pH of the process acommon step in ensuring accuracy is tohave the lab do a grab sample analysis.Difficulty can occur when the lab resultsdo not correspond to the process analyzer,which is surprisingly common due todiscrepancy between lab and processsample conditions.

A common lab analysis procedure is asfollows: a grab sample is taken to the labin an open container within approximately15 minutes and placed on the lab bench.The bench meter is calibrated in about5 minutes and a non temperaturecompensated pH reading is taken of theprocess. This grab sample procedure has ahigh potential for discrepancy between thetwo sample conditions. First, the timebetween sample being taken and the lab pHmeasurement was approximately20 minutes. In this time the sample willcool down. As the sample cools thesolution chemistry changes and thus thepH measured at the cooler temperature willnot be indicative of the pH measured atsample conditions. A good indicator thatsolution temperature affects pH is buffersolutions which have temperature curvesassociated with them. Buffers arespecifically designed to resist pH change.

A second problem relates to temperaturecompensation of the lab analyzer. As seenin the Heat Effect on Slope section, it is




very important to have correct temperaturecompensation to ensure that accurate pHreadings are reported.

A third point relates to contamination. Thelab sample was in an open beaker andwalked through an industrial plant withcontaminants in the air. As the openbeaker is carried through the plant it willlikely pick up some of these airbornecontaminants which could alter the pH ofthe sample.

Therefore, when noting the differencebetween a grab sample pH and the processpH, it is important to ensure that the grabsample measurement is performed at thesame sample conditions as the process sothat the two readings are comparable. Infact, because the process pH electrode doesnot get exposed to these potential sourcesof error it may well be more accurate thana grab sample.


IC Controls INSTALLATION

INSTALLATION

Selecting the Location

For the pH sensor to work reliably, theinstallation location must ensure that thepH electrode is always completelyimmersed in liquid. To respond well, thesensor must be positioned in some flowwhere it sees the change in pH (eg. afterthe leak point). Long sample lines shouldbe avoided wherever the pH signal must beresponsive to sudden changes to avoidsample transport lag problems. Care mustbe taken to ensure any bubbles entrained inthe liquid will not pass through the pHsensing tip as the void they create in themeasuring circuit will reduce the ionconnection and produce erroneous results.Similarly, solids or sludge should be takeninto account that may coat the electrodes;position the sensor to pick-up only thecleanest possible sample. The installationshould also provide for easy sensorcalibration with adequate room for sensorremoval plus 1 m (3 ft) of flex-conduit forcalibration.

Analyzer Location

The sensor is typically supplied with atleast a 1.5 m or 5 ft lead (model 642 has3 m or 10 ft) as standard. The analyzershould be kept within the sensor leadlength, and mounted typically on a wall ateye height. Position the analyzer to allowthe sensor, still connected, to be removedand the electrode tip placed in a beaker onthe floor for cleaning or calibration.Assume the safest place for the beaker ison the floor the service person stands on.Horizontal separation between rows ofanalyzer should allow for electrode leadswhich need periodic replacement, and the

electrical conduit. IC Controlsrecommends 10 cm (4 in) minimumseparation between rows/columns.

Pipe mounting kits for 5 cm (2 in) pipe,are also available. They may also be usedto surface mount the transmitter byremoving the two inch U bolts and usingthe holes in the mounting plate for wallstuds (using customer-supplied studs).

Panel mounting kits are also available.These require a customer-supplied panelcut-out.

pH Sensor Mounting

It is recommended that the pH sensor belocated as near as possible to the pHtransmitter to minimize any effects ofambient electrical noise interference.

pH sensors can be in any orientation butshould be mounted tip down at an angleanywhere from 15 degrees abovehorizontal to vertical; 15 degrees abovehorizontal is best because air bubbles willrise to the top and grit will sink, bothbypassing the sensor.

Submersion sensors should not be mountedwhere a lot of air bubbles will rise in thetank; they will cause spikes in the pHreadout. If a bubble is allowed to lodge in

the sensingtip,electricalcontinuitybetween theelectrodesmay bedisrupted.


Illustration 10: Sensor mounting

Min 15

Max 90


INSTALLATION IC Controls

Flow Mounting

Flow type installations available are:

1) Flow housing with 1½ inch FNPTconnections for use with model 625Quick Union Sensors:CPVC, option -21, P/N A2300073.PVDF, option -22, P/N A2300074.316 SS, option -23, P/N A2300075.

2) 316 SS flow housing for 615 HighPurity pH sensor used on pure waterapplications (option -21 for 615); P/N A2100059.

Install the housing at 45 degrees orvertically and position the sensor so thatthe tip is below the outlet. This will ensurethe sensor is in sample at all times, even ifthe exit pipe drains to atmosphere and aircan enter. Flow should be upwards and outthe side, thereby flushing any bubbles outof the cell area.

The housing can be used as an in-line bodyor in a side stream line. Always place onthe pressurized side of a pump, not thesuction side, and if using as an in-linearrangement, allow for the added flowresistance caused by the sensor body.

Insertion Mountings

If the vessel will be full at all times whenthe pH needs to be measured, the sensorscan be inserted into a threaded opening.The location must ensure the sensor is at15 degrees above horizontal, fullysubmerged and not subject to blanketingwith deposits. Removal clearance isnecessary with any insertion sensor andusually 12 inches is sufficient.

Insertion type installations available are:

1) “Threaded in” pH sensor insertion with1 inch MNPT on tip of 642 [option -21(X)].

2) ¾ inch NPT SS gland fitting insertionfor use with 605 (option -74), P/N A3100002; titanium (option -75), P/NA3100003.

3) 1 inch NPT SS gland fitting insertionfor use with 607 (option -74), P/N A3100175; titanium (option -75), P/NA3100095.

4) Quick union insertion fitting with 1½inch MNPT connections for 625 sensor:CPVC, option -26, P/N A2300086; 60 psi at 90 C.PVDF, option -27, P/N A2300087; 90 psi at 90 C. 316 SS, option -28, P/N A2300088;100 psi at 150 C.

WARNING! The major consideration forinsertion mounting is that a hole exists inthe vessel/pipe wall if the sensor isremoved for calibration, etc.. Insertionsensors are often called “Hot Tap”because a solid stream of hot processliquid will escape if the sensor is removed,unless the pressure and level are loweredbelow the hole.


Illustration 11: Recommended piping


Ball Valve Retractable Mountings

The IC Controls model 606 and 617 ballvalve insertion/retractable sensors weredeveloped to handle the problem when thepressure/level cannot be lowered below thehole; similar ball valve options areavailable on model 605 and 607. Whenused, the benefits and economy of nosampling system are available, even wherethe process must stay pressurized ordraining the system would be costly.

Removal clearance is necessary. With the606 and 617 retractable sensors and the605 and 607 retraction options, 30 inchclearance is needed; the sensor normallyextends about 18 inches from the mountingopening.

Ball valve insertion assemblies require aweldlet (pipe fitting welded on a pipe)mounted on an angle of 15 degrees orgreater above horizontal to keep airbubbles out of the pH tip.

Ball valve insertion/retractableinstallations available are:

1) 1 inch NPT, SS ball valveinsertion/retractable assembly; for 606pH sensor with safety anti-blowout lip;option -21, P/N A2100071.

2) 1¼ inch NPT, SS high pressure ballvalve insertion/retractable assembly; for617 pH sensor, option -21, withisolation chamber; chamber retainsflashing process liquid.

3) 1 inch NPT, ball valveinsertion/retractable assembly; for 605pH sensor; SS option -21, P/N A2100052; titanium option -23, P/NA2100055; PVDF option -26, P/N A2100054.

4) 1 inch NPT, ball valveinsertion/retractable assembly; for 607pH sensor; SS option -21, P/N A2100253; titanium option -23, P/NA2100209.

Pulp & Paper Stock Mountings

IC Controls model 605 and 606 ball valveinsertion/retractable sensors have optionalfitting sets with water injection ports foruse on dense pulp stock applications.Before the pH sensor is inserted, purge theinsertion opening with pressurized water;this will push out de-watered stock thatmay be plugging the opening. Model 617handles the problem even with highpressure, up to 300 psi.


Illustration 12: Direct insertion installation

Illustration 13: Ball valve insertion



Ball valve insertion/retractable fitting sets:

1) For 606 pH sensor; 1 inch NPT densestock flush fitting set; SS option -24, P/N A3100241; titanium option -25, P/NA3100242 PLUS ball valveinsertion/retractable assembly; SSoption -21, P/N A2100071; titaniumoption -23, P/N A2100072; PVDFoption -26, P/N A2100073.

2) For 605 pH sensor; 1 inch NPT densestock flush fitting set; SS option -24, P/N A3100062; titanium option -25, P/NA3100126 PLUS ball valveinsertion/retractable assembly; SSoption -21, P/N A2100052; titaniumoption -23, P/N A2100055; PVDFoption -26, P/N A2100054.

Submersion Mountings

All IC Controls submersion pH sensorshave the electrodes sealed in epoxy to stopliquid leaking into the internals andshorting problems, plus, provision for an“industrial pH interface” mounted on topof the sensor support pipe (refer to drawingD4850015). The 600 industrial pHinterface makes a convenient point todisconnect the pH sensor for inspection,cleaning or other service, plus itstrengthens the weak pH signal so it can gothousands of feet (maximum without

interface is 100 ft). Alternativearrangements use a 600-71 surfacemounted pH interface, or a directconnected pH analyzer or transmitterwithin 3 m (10 ft).

The submersion sensor should be locatedwhere there is sufficient flow or agitationto ensure a representative sample reachesthe pH sensor; stagnant spots such ascorners should be avoided. Sensors withflutes around the pH glass electrode arepreferred for submersion service; inservices where abrasive grit or gravel isentrained in the liquid. Flat pH glass mayachieve further resistance to impact.

NOTE: Flat pH glass is not as good onhot or cold applications since the thermalexpansion causes a shearing action thatwants to “pop-off” the tip, whereas,standard round pH glass tends to absorbthermal expansion stresses.

Heavy Industry 642

For industrial sewers, mine flotation cells,tanks and other dirty applications, the 642pH sensor presents an easy to cleansolution with clearance for screwdrivercleaning around the pH glass. Its flutesalso provide protection from impact on thebottom or from floating debris. Thisindustrial pH sensor is big and rugged,built in a heavy Schedule 80 pipe; itscushion mounted glass electrode cansurvive extreme impact and still providereliable service.

Submersion can be 3 m (10 ft) withstandard 642 sensors, however, longerleads can be special ordered. The 642would preferably be mounted on a0.75 inch NPT thread on the end of a0.75 inch SS pipe for best rigidity, orSch. 80 PVC pipe where whipping due toflow resistance will not present a problem.


Illustration 14: Dense stock flush installation


IC Controls recommends mounting a 600pH interface and J-box on top of the pHsensor support pipe. For ease ofcalibration, allow pipe length plus 1 m(3 ft) extra of flex-conduit, and wherepossible, install the support pipe on arailing with easy access for quickdisconnect.

Light Industry 602

For cleaner light industrial applicationsand effluent streams, the 602 pH sensorcan be used. Its flutes also provideprotection from impact on the bottom orfrom debris. This light industrial pHsensor is rugged, built in a lighterSchedule 80 pipe. Its shock mounted glasspH electrode can give years of reliableservice.

Submersion can be 1 m (3 ft) with standard602 sensors, however, longer leads can bespecial ordered. The 602 should preferablybe mounted on a 0.75 inch FNPT thread onthe end of a 1 inch Sch. 80 PVC supportpipe.

Strong SS Industrial 605 OR 607

For demanding industrial applicationswhere stainless steel is required, the 605 or607 pH sensors can be used. These alsohave flutes to provide protection fromimpact on the bottom or from debris.These industrial pH sensors are strong,built in a 316 SS tube; they handle roughapplications where plastics do not survive.Its shock mounted glass pH electrode givesyears of reliable service and its smalldiameter resists the bending forces of fastflow and entrained materials.

Submersion can be 1 m (3 ft) with standardmodels, however, longer leads can bespecial ordered for greater depths.Mounting of 605 is preferred on a ¾ inch

FNPT thread on the end of a 1 inch Sch. 80SS pipe using the supplied fitting, P/N A3100002 (605 option -74). The 607mounts similarly on a 1 inch FNPT threadon the end of a 1¼ inch Sch. 80 SS pipeusing P/N A3100175 SS insertion glandfitting (607 option -74).

Sensor Wiring

pH is a Very Tiny Signal

History has shown that pH electrodesignals can easily be disturbed because theglass pH electrode outputs a very tinysignal. IC Controls strongly suggests theuse of an industrial pH interface thatstrengthens the signal so it has a reasonablechance of remaining stable in a plantenvironment. pH electrodes have a veryhigh impedance which makes their leads agood antenna that easily picks up electricalnoise in a plant. Long leads are longantennas and often result in unstable pHreadings. A 600 industrial pH interfaceeliminates the problem and connectionscan be extended to thousands of feet.


Illustration 15: Model 600 industrial interface



Never Cut and Splice pH Leads

All pH sensors are supplied with a highimpedance connector, typically a BNC,which is designed to ensure thatfingerprints, dust and moisture do notdeplete the almost non-detectable pHsignal. It is very difficult to make a fieldsplice without leaving some deposits thatnormal humidity on a dry day can turn intoa signal drain and dispel pH signal. Theonly splice method known to work reliablyfor pH is to use a pH extension cable, or anindustrial pH interface. The cable isavailable from IC Controls as P/N A9200006, or locally as Belden 9535.

Take care to route all sensor wiring awayfrom AC power lines to minimizeunwanted electrical interference. Wheninstalling pH sensor cable in conduit, usecaution to avoid scraping or cutting thecable insulation; the resulting short of thecables' internal shield will cause pHground loop errors. As well, avoidtwisting the sensor lead to minimizepossibilities for broken wire.

Direct Connected pH

In areas where electrical interference is nothigh, direct connection from pH sensor to apH analyzer with option -6 integral highimpedance input can be used for distancesless than 30 m (100 ft).

IC Controls' pH sensors are supplied withthree leads. The black coax lead with BNCconnector is always connected to thesensor pH electrodes. The center lead andshield (outer) lead of the coax should beinsulated from each other as well as fromthe red and white temperature compensator(TC) leads, with insulation to ground forall leads. TC leads are polarity specificusing -33 IC Controls TC; red is TC

positive and white is TC negative.

Instrument Shop Tests

Checking the Sensor

The sensor should be checked against theordered specification to ensure the correctsensor for the job is used. Refer tospecification sheets and sensor selectionguide to confirm the model numberreceived. Electrical checks may be madeto ensure the sensor is in good conditionbefore installation. Between the BNCcenter and outer housing, pH glassresistance should exceed 20 M.

Between the red and white temperaturecompensator leads, there is either a semi-conductor (option -33) which un-powered,appears open circuit, or an RTD; theresistance values given for the TC at 25 Care 3000 (option -31), 110 (option -32) or 1096 (option -34). Betweeneither TC lead and either cell lead thereshould be insulation values exceeding20 M.



Preparation for Use

1) Moisten the sensor body with tap waterto remove any salt deposits, thenremove the plastic cap from electrodetip. Rinse the exposed pH electrodeswith tap water making sure all saltcrystals and/or other deposits areremoved.

2) For first time use, or after long termstorage, immerse the lower end of thesensor in a 4 pH buffer for 30 minutes.This conditions the pH glass electrodeand prepares it for stable readings inother buffer solutions.

NOTE 1: IC Controls sensors are shippedpacked in pH electrode storage solution.Storage solution extends the life of thereference pH electrode which after longterm storage may give short service life;however, when first unpacked, the pHresponse may be slow.

NOTE 2: For new pH sensors, it isrecommended to soak the sensors in pH 4buffer and calibrate with pH 7 as bufferone and pH 10 or pH 4 as buffer two -depending on the normal application pH -to achieve good accuracy. If duringbuffering the pH sensor seems slow, cyclea few times from pH 4 buffer to pH 10buffer to “wake-up” the pH glass response;it should speed up noticeably.

NOTE 3: Packed in storage solution, pHelectrodes are often ready for useimmediately with typical accuracy of± 0.2 pH without calibration.

Testing with the Analyzer

Refer to the analyzer instruction manualfor proper wiring instructions unique to it.

1) Apply power to the analyzer.

2) Hook up the sensor and remove theprotective cap.

3) With the sensor in pH 7 buffer, the pHanalyzer should display a reading of7.0 pH ± 0.5 pH.

4) Run a “zero” calibration; 7 pH isequivalent to 0.0 mV so use pH 7buffer. If possible, use the pH extensionwires to be field installed and allow30 minutes warm-up time for theelectronics to stabilize.

5) Run a “span” calibration by placing thesensor in pH 4.01 buffer. The displayshould read approximately 4.01 pH± 0.05 pH.

6) To check for general performance, placethe pH sensor in pH 7 buffer again. Itshould now read approximately 7.0 pH± 0.05 pH.

7) The sensor is now ready for fieldinstallation.

8) If the application will be in the causticregion, repeat steps 5 and 6 using pH 10buffer so that the sensor is tested in theregion of use.



pH CALIBRATION IC Controls

pH CALIBRATIONThe pH sensor-analyzer system is usuallycalibrated using standard buffer solutions.Alternatively, grab-sample analysis on apreviously calibrated lab reference pHmeter can be used.

pH is proportional to temperature. Theeffect is predictable and repeatableaccording to the Nernst equation.

Overall system accuracy is maintained bycalibrating the pH sensor and analyzertogether in a buffer close to the expectedsample pH. The pH electrode efficiencyand offset (or standardize) will change overtime as the pH glass ages, deposits form,and the process affects the electrodesurface.

Selecting a pH Buffer

pH buffers provide the simplest and mostaccurate method of calibrating the pHsensor and analyzer.

First Buffer: The first step is to use 7 pHbuffer to calculate the mV offset of theelectrode from the theoretically perfect0 mV. pH 7 buffer is used because itsimulates 0 mV thus making it the beststandard since the electronics are also atthis 0 mV reference point.

Second Buffer: The next step in thecalibration is to use a second buffer(usually 4 pH or 10 pH). When choosingwhich buffers to use in calibration, it isbest to select buffers that fall on both sidesof the normal operating pH range. Byusing these two buffers, the slopecalculation will encompass the normal pH,thus giving the most accurate pHmeasurement. Either of these buffers,pH 4 or pH 10, gives a large enough spacerelative to the pH 7 buffer that a good

slope can be calculated. When performingthe two point calibration, a percent valuewill be given in microprocessor based pHanalyzers. The closer to 100% the slope is,the better the efficiency and thus theperformance of the electrode.

Some analyzers such as IC Controls 655have been programmed to recognize thethree buffers most commonly used forcalibration: pH 4, pH 7, and pH 10. Toachieve greater accuracy, the temperaturecompensated values for these buffers arecalculated by the analyzer. Simply placethe electrodes in the buffer solution and theanalyzer will select the correct buffervalue, allowing for an offset of up to± 1.3 pH units.

Temperature Dependence of Buffers

The pH of a solution is dependent ontemperature. To achieve greater accuracy,the temperature-compensated values forthe 4 pH, 7 pH and 10 pH buffers arecalculated by IC Controls analyzers.

The following graphs show thetemperature-dependence of the standardbuffers. The TC-curves have beenprogrammed into IC Controls analyzers.The actual pH value of each of the threestandard buffers will be used.


Illustration 16: Temperature compensated pH 4 buffer

IC Controls pH CALIBRATION

Example: Calibrate using the pH 4.01buffer (at 25 °C). The temperature of thebuffer is 50 °C. The analyzer will use thepH value of 4.05.

Incorrect Buffer Selection by theAnalyzer

If the offset is known to be greater than ± 77 mV, or if the analyzer selected the wrong buffer using automatic buffer recognition, then it is necessary to specify which buffer is being used. This is done by selecting [4.01], [7.00], or [10.0] then an offset of ± 4 pH units is allowed and temperature-compensated values are still used.

Other Buffer Values or CustomBuffers

If a buffer with a pH value other than pH 4,pH 7, or pH 10 is to be used, select“custom value”, then enter a value between0 pH and 14 pH. Buffer values enteredthis way are not temperature compensated;the buffer is assumed to have the specifiedpH value at the current temperature.Offsets of up to ± 4 pH units are allowed.

Electrode Life

The electrodes need to be calibratedperiodically to maintain accurate pHmeasurement. IC Controls recommendselectrodes be calibrated every 30 days.Depending on the process, they may needto be calibrated more frequently, eg.weekly or even daily. More frequentcalibration is important if high accuracypH measurement is required.

Over time, electrode performance willdegrade. The pH glass becomes lessresponsive to pH and the referenceelectrode becomes depleted. Expect thatelectrodes will need to be replaced afterseveral years of use, or sooner, dependingon the harshness of the application.






Standardizing Single-Buffer Calibration

Standardizing the pH sensor causes theanalyzer to calculate the offset for the pHsensor. The electrode slope valuedetermined during the last [buF2]calibration (or theoretical 100%) will beused.

NOTE: The following instructions arebased on an IC Control microprocessoranalyzer.

1) Rinse the pH sensor in deionized waterto remove drops of process liquid.Although pH buffers are formulated toresist pH change, mixing in strongforeign ions can cause pH shift andresultant calibration to an incorrectbuffer value. Dirt deposits, biologicalgrowths, and any other contaminantsshould be removed from the pH sensorbody and tip before calibration.

2) Select the buffer with which tocalibrate. Refer to the section Selectinga Buffer for details. Place the pH sensorin the buffer solution.

3) Press SAMPLE to display pH reading.Press SELECT to view the main menu,then press the ↑ key to display [pH].

4) Press SELECT again, then use the ↑ keyto display [Cal]. Repeat to get [buF1].

5) Press SELECT again to reach the nextmenu. Use either automatic detection, acustom value, or one of the standardbuffers, pH 4, pH 7, or pH 10.

6) With the electrode in the buffer solutionpress SELECT to start the calibrationprocess. The display will show aflashing pH reading to indicate that theanalyzer is reading pH in calibrationmode and is waiting for the pH to

stabilize.

As soon as the electrode has stabilized, thedisplay will stop flashing, the electrodeoffset will be calculated, and the new offset(standardize) will be entered in memory.

The [ENTER] key may be pressed beforethe electrode has stabilized, forcing theanalyzer to calibrate using the current pHinput, resulting in a lower precisioncalibration.

7) Confirm the single point calibrationprecision by repeating the calibrationsteps 1 to 4. There should be closeagreement between the readings and thebuffer, however, small adjustments maybe handled by repeat calibrations.

If the temperature is far from 25 °C, theanalyzer will display the temperaturecompensated pH of the pH buffers. Referto Selecting a Buffer section for moreinformation.

Calibrations may be redone or started overat any time. Press SAMPLE to display thepH then SELECT as needed to restart thecalibration.

If the analyzer detects a problem duringcalibration, a caution or error message willappear. A caution message informs theuser that poor pH electrode performance issuspected and will be compensated for bythe microprocessor. If an error message isdisplayed, the electrodes exhibit majorproblems; the standardization was notsuccessful. The analyzer will still operate,but will use the values from the previouscalibration.

8) Press the SAMPLE key to resumenormal operation after a caution or errormessage has appeared.

The pH sensor is now standardized, and



will be accurate at pH readings close to thepH of standardization.

For best accuracy over wider pH ranges,finding the pH efficiency or slope usingtwo buffers is recommended.

Discard used buffer after calibration. Usedbuffer has usually picked up carry-overcontaminants or biological growths thatcause pH error if re-used.

Calibrating Two-Buffer Calibration

Fully calibrating the pH sensor involvescalculating both the offset and the pHelectrode efficiency or slope to match aparticular electrode pair. The electrodeslope will be calculated as a percentage ofNernstian response (59.16 mV per pHunit).

1) Calibrate the offset with pH 7 buffer as[buF1] by following the procedure forStandardizing Single BufferCalibration above.

2) Rinse the pH sensor in deionized waterto remove drops of pH 7 buffer.

Carry over of old buffer into different freshbuffer will decrease the pH differencebetween the buffers producing anefficiency calibration error.

3) To calibrate with the second bufferpress SAMPLE to return to the pHdisplay. Then press SELECT to display[pH] and again as needed to reach thebuffer selection menu. Press the ↑ keyto display [buF2].

The second buffer should be at least 2 pHunits higher or lower than the buffer usedfor the standardize procedure. For furtherdetails refer to Selecting a Buffer for anexplanation of the buffer selection process.

4) Use the ↑ key to display eitherautomatic buffer recognition, a customvalue, or one of the standard buffers, pH4, pH 7, or pH 10. Press SELECT tocommence the calibration process.

5) As soon as the electrode has stabilizedthe display will stop flashing, theelectrode slope will be calculated, andthe new slope (efficiency) will beentered into memory. The analyzer willadjust its pH display.

6) Confirm the efficiency calibrationprecision by repeating the calibration,steps 2 to 5. There should be closeagreement between the readings and thebuffer, however small adjustments maybe handled by repeat calibrations.

If the temperature is far from 25 °C theanalyzer will display the temperaturecompensated pH of the pH buffers. SeeSelecting a Buffer section for moreinformation.

Calibrations may be redone or started overat any time. Press [SAMPLE] to displaythe pH then [SELECT] as needed to restartthe calibration.


Illustration 19: Standardize



If the pH sensor exhibits a problem duringcalibration, a caution or error message willappear. A caution message informs theuser that poor pH electrode performance issuspected and will be compensated for bythe microprocessor. If an error message isdisplayed, the electrodes exhibit signs ofmajor problems; and the efficiencycalibration was not successful. Theanalyzer will operate, but using the valuesfrom the old calibration.

7) Press the [SAMPLE] key to resumenormal operation after a caution or errormessage has appeared.

The pH sensor is now fully calibrated, andwill be accurate at pH readings betweenthe pH of the buffers used, as well as a fewpH units beyond.

Discard used buffer after calibration. Usedbuffer usually picked up carry-overcontaminants or biological growths thatcause pH error if re-used.

Grab Sample At Process Calibration

The grab sample method provides an easyway to calibrate the pH sensor bystandardizing to the process pH, withoutremoving the pH sensor from the process.Grab sample standardization requires theuser to determine the actual pH of theprocess using a different method. Forexample, if the analyzer is reading 3.55 pHand a laboratory analysis determines theactual pH of the sample to be 3.42 pH, thegrab sample method can be used to adjustthe offset so that the previous 3.55 pHreading changes to 3.42 pH.

The precision of standardization using thegrab sample method is only as accurate asthe values supplied to the analyzer by the

operator.

1) Obtain the following materials: asecond high accuracy pH analyzer, aquality pH electrode and fresh pHbuffers for calibrating it, and a newclean beaker or sample bottle to collecta “Grab Sample”.

2) Perform a high accuracy Two BufferCalibration on the high accuracy pHanalyzer, and record the date andresults.

3) Extract a grab sample of the processwhich is representative of the solutionthe pH sensor is in, preferably from justbeside the sensor.

4) At approximately the same time that thethe grab sample is taken, store thecurrent pH in the on-line analyzermemory by selecting [pH][CAL][GrAb][GEt] from the menu. Press [ENTER]at the flashing [do].

It is important that the pH value recordedin memory represents the pH of thesample. This is easy to accomplish if theanalyzer has a stable reading, but difficultif there is a lot of fluctuation in the pHreading. This step can be repeated as oftenas necessary.

It is possible to view or even change thepH value recorded in memory. Select [pH][CAL][GrAb][OLd].

Analyze the grab sample to determine theactual pH.

For maximum accuracy, the temperature ofthe sample should be the same as it was atthe time the old value was recorded, using[GEt]. A significantly different pH couldresult if there is a temperature difference.



5) Select [pH][CAL][GrAb][SEt] from themenu. Edit the pH value using[ENTER] and the arrow keys, andchange it to the new pH value. Thenpress [SELECT] then press [ENTER]with the flashing [do] displayed. Theoffset will be adjusted according to thedifference between the old and new pHvalues.

The error checking done for the grabsample calibration is similar to that donefor a [buF1] standardization. An offsetwarning, CA1.6, is given if the new offsetis greater than 1.3 pH units fromtheoretical behavior. If the new offsetwould be greater than 4.0 pH units thenerror 1.3 is generated and the new offsetwill not be recorded.



INSERTING/REMOVING pH SENSORS IC Controls

INSERTING/REMOVING pHSENSORS

Preparation for Use

1) Moisten the pH sensor body with tapwater and carefully remove the tape andplastic storage cap. CAUTION shouldbe used in removing this cap; pullstraight down. Do not bend the body ofthe pH sensor. This can result indamage to the internal element.NOTE: Save this lower cap for use instorage of the pH sensor.

2) Rinse away any deposits on the exposedpH bulb and junction area with tapwater.

3) For the first time use, or after long termstorage, immerse the pH electrode in4 pH buffer for 30 minutes. Thishydrates the pH bulb and prepares thereference for junction for contact withtest solutions.

4) If air bubbles are visible inside the pHbulb, shake the electrode downward tofill the bulb with solution.

5) IC Controls electrodes are shipped in apH electrode storage solution bufferedto approximately 7 pH. Theseelectrodes are often ready for useimmediately with typical accuracy of± 0.2 pH without buffering; however itis recommended that bufferedcalibration be performed.

6) The pH sensor is ready to be placed inservice.

Inserting pH Sensors

Insertion sensors should be examined forgood clean sealing surfaces and installedcarefully. Clean seals such as O-ringsshould be lubricated with silicone grease toensure liquid tight performance.

Remove the storage cap then carefullypush the sensor into the insertion fittinguntil it is seated against the stops. Tightenthe retainer nut to hold the sensor firmly inplace.

Let the vessel fill with liquid.

The pH sensor should now read the liquidpH.

605-21 & 606-21 Ball Valve Sensors

WARNING! The system pressure must beless than 100 psi.

1) Inspect and clean the O-ring, glandfitting and sensor body; replace ifnecessary.

2) DO NOT open the ball valve. Carefullypush the sensor into the ball valve until,for 605 the safety cables can be screwedinto the ball valve body, or for the 606,the positive stop gland can be screwedinto the ball valve bushing.

CAUTION! Do not pass this point.Damage to the glass pH tip could result.

3) Once screwed in, pull on the pH sensorto make sure it cannot come free fromthe ball valve.

4) Tighten the gland nut, hand tight.

5) While restraining the sensor housing byholding the junction box, slowly openthe ball valve.

6) Insert the sensor until the pH tip is


IC Controls INSERTING/REMOVING pH SENSORS

about where desired in the process.Measure and pre-mark if needed. Thisis recommended on less than 8 inchdiameter pipe.

7) First time installation of the sensorhousing, turn the nut on the Swagelokfitting until it is finger-tight and then,using wrenches, tighten the nut 1¼turns.Re-installation, turn the nut on theSwagelok fitting no more than ¼ to ½additional turn after finger tight.

Modified Insertion Dense Stock Applications

CAUTION! Great care must be taken toavoid breaking the electrodes against astock plug which can be as solid as a wetpiece of wood.

1) Before attempting insertion, clean-outthe valve and fitting assembly byhooking up a ¾ inch water tube line tothe ¾ inch gland fitting in place of thepH sensor. Provision must also bemade to permanently hook up a ⅜ inchwater flush line with shut off valve tothe side flush fitting (refer toillustration 14).

2) Open the ball valve and blast any plugout with high pressure water. Shut offthe ball valve with the water pressureon.

3) Refer to drawing D4840014 as perillustration 20. The objective is to placethe pH tip in the liquor pad. This can bedone by using the pH sensor, however amistake will result in a destroyedelectrode. Alternately, accurate pre-measurement will give a good positionfor scribing the sensor body with a linefor insertion depth. A second

alternative uses a ¾ inch diameterstainless steel rod to feel the plug. Aflat holder such as the J-box and endfittings must be installed on the rod sosafety cables can be hooked up toprevent a slip, allowing the rod tobecome a projectile. Keep the waterflush flow on while probing for thestock plug.

4) Scribe the sensor body at the desiredinsertion point, about 5 mm (⅛ inch)back from the plug.

5) Prepare for pH sensor insertion. Ensurethat the stainless steel ferrule is beingused. Inspect and clean the O-ring,gland fitting and sensor body; replace ifnecessary.

6) DO NOT open the ball valve. Carefullypush the sensor into the ball valve until,for 605 the safety cables can be screwedinto the ball valve body, or for the 606,the positive stop gland can be screwedinto the ball valve bushing.

CAUTION! DO NOT pass this point.Damage to the glass pH tip could result.

7) Once screwed in, pull on the pH sensorto make sure it cannot come free fromthe ball valve.


Illustration 20: Drawing D4840014


INSERTING/REMOVING pH SENSORS IC Controls

8) Tighten the gland nut, hand tight, thenopen the ball valve slowly.

9) Turn on purge water to help insert thesensor. Check that the stainless steelferrule is being used, then press sensorin only to the scribed line. Using the SSferrule, lock the sensor at this depth.

10)First time installation of the sensorhousing, turn the nut on the Swagelokfitting until it is finger-tight and then,using wrenches, tighten the nut 1¼turns.Re-installation, turn the nut on theSwagelok fitting no more than ¼ to ½additional turn after finger tight.

11)Keep the water flush flow on low whilemeasuring pH. This resists stockpacking in around the sensor, howeverif too much water is used it will alsoimpede pH accuracy. Some testing willdetermine the best setting for eachapplication.

pH Sensor Removal

CAUTION! Use rubber gloves andappropriate face/eye protection whenhandling sensors coated with aggressiveliquids.

Sample Line Sensor Removal

Simply turn off the sample flow and allowthe sample line pressure to drop to zero,then undo the retaining nut and remove thepH sensor.

Submersion Sensor Removal

Submersion installations can typically belifted out with the concern being liquid onthe support pipe or wires.

CAUTION! Use rubber gloves and

appropriate face/eye protection whenhandling sensors and long submersionsupport pipes coated with aggressiveliquids.

Insertion Sensor Removal

WARNING! Before pH sensor removal,the process pressure must be lowered tozero, or a dangerous pressurized stream ofprocess liquid will blast out.

Sensor models 614 and 625 leave a hole inthe line, vessel or tank when removed, andare intended for use only where pressurecan be lowered to zero for servicing. Useof model 605, 606, 607, or 617 ball valveinsertion/retractable sensors arerecommended where pressure cannot bereduced to zero for service.

Vessels and tanks must be drained until theliquid level is below the sensor insertionhole for the pressure to be zero and noprocess liquid to escape.


IC Controls INSERTING/REMOVING pH SENSORS

Removal 605-21 & 606-21 BV Sensor

1) Inspect the safety cables and replace ifcorroded or damaged; P/N A1100011.

CAUTION! On hot processes there is arisk of pressurized steam or liquidescaping. The gland has two seals toreduce this risk but scratches and grit mayreduce effectiveness.

2) Release the gland nut slowly about 2 or3 turns, allowing the pH sensor body toslide back until the stop is reached orthe safety cables are tight.

3) Pull to ensure the pH sensor is fullyretracted, then shut off the ball valve.

4) Only with the ball valve closed, removethe gland nut completely.

5) With the ball valve still closed, unscrewthe positive stop gland (606) or safetycables (605) from the valve housing.

6) The pH sensor body can now beremoved.

Modified Removal Dense Stock Applications

1) Inspect the safety cables and replace ifcorroded or damaged; P/N A1100011.

2) Open the ⅜ inch water flush line toclear any stock buildup in the gland,ball valve, or fitting assembly.

CAUTION! On hot stock there is a risk ofpressurized steam jets or liquid escaping.The gland has two seals to reduce this riskbut scratches and grit may reduceeffectiveness.

3) With flush water flowing, release thegland nut slowly about 2 or 3 turns,allowing the pH sensor body to slideback until the positive stop is reached(606) or the safety cables are tight(605).

4) Pull on the pH sensor to ensure it isfully retracted, then shut off the ballvalve, and then the flush water.

5) Only with the ball valve closed and theflush water off, remove the gland nutcompletely releasing any pressure.

6) With the ball valve still closed, unscrewthe positive stop gland (606) or safetycables (605) from the valve housing.

7) The pH sensor body can now beremoved.



SENSOR MAINTENANCE IC Controls

SENSOR MAINTENANCE

Sensor Storage

Short Term: Rinse the pH sensorelectrodes in deionized water then store ina plastic shipping cap of 4.0 pH buffersolution.

Long term: Clean the pH sensorelectrodes in pH electrode wash solution,P/N A1100091, rinse in deionized water,then store in a plastic shipping cap full ofpH electrode storage solution, P/N A1100090.

Monthly Maintenance

Remove the sensor, rinse in water, removeany significant deposits, and then check bycalibration in 7 pH for offset and then 4 pHor 10 pH buffer for slope; refer toCalibration section for completeprocedure. Alternatively, if the sensor isinstalled in the process and not easy toremove, follow the procedure in the GrabSample Calibration section of this manual.

If the calibration turns up a caution or errormessage in the analyzer, then follow theappropriate troubleshooting procedure.

If the calibration is good, keep a log of thepH offset and efficiency at each monthlycalibration.

The pH sensor is now ready to return toservice.

Yearly Maintenance

Examine the condition of electricalconnections in 600 junction boxes for signsof corrosion and tight connections, replaceif corroded. O-rings and teflon-sealingferrules should be replaced on 605, 606,607, 614, 617 and 625 sensors. Thecondition of the safety cables on 605sensors should be examined for rust or bentmounting screws. Replace if deteriorationis evident.

Check the pH offset log. If the pH offsethas changed more than 30 mV over thepast year, it may need to be chemicallycleaned – follow the Chemical Cleaning ofSensor procedure.

Check the pH efficiency log. If theefficiency has dropped below 80%, it mayneed to be chemically cleaned and restored– see Chemical Cleaning of Sensor and/orRestoring Electrode Response.

After all the above checks, plus chemicalcleaning and/or restoring procedures,follow the monthly maintenanceprocedure. Start a new log with theimproved values.

Sensor Cleaning

Various factors can affect the pH reading;scale, biological growth, oils, wax, gum,etc. all reduce the area for hydrogen ion toreact with the glass. Biological microbegrowths can also produce local pHenvironments inside their growth deposit,which can be quite different from the trueprocess pH. Periodic cleaning of pHsensors will remove these deposits, restorethe pH glass surface, reference junctionand thus the pH accuracy.


IC Controls SENSOR MAINTENANCE

Mechanical Cleaning of Sensor

The sensor will require cleaning if sludge,slime, or other deposits build up in theinternal cavities of the sensor.

Wherever possible, clean with a soft brushand detergents. General debris, oil, films,biological growths, and non-tenaciousdeposits can be removed in this way. Themodel 642 has 2.5 cm (1 inch) junctiondiameter and open slots, chosen so astandard flat screwdriver blade can be usedto scrape scale and other tenacious depositsoff the reference junction quickly. Also,the model 642 open tip design allows thescrewdriver to carefully score and crackhard scale against the glass shaft thencarefully slide it up and off the pH glass tipwithout touching the pH glass, whichwould damage it.

For flat-surface sensors, use a soft flatbrush and a beaker or bucket of water witha good liquid detergent. Take care not toscratch the pH electrode glass surface, it isthin, fragile and easily broken.

All the wetted surfaces of plastic bodysensors should be washed with a soft cloth.This will return their appearance to like-new condition and removes sites forbuildups to occur.

When to Chemical Cleaning

After mechanical cleaning, as above, checkthe sensor against a pH buffer. If thesensor is still not developing the pHreading properly in the pH buffer, proceedto the chemical cleaning procedure,otherwise return the sensor to the process.

Chemical Cleaning of Sensor

A1600054 pH Chemical Cleaning Kit

P/N A1600054 is a pH sensor chemicalcleaning kit containing solutions andnecessary cleaning items. It contains thefollowing:Cleaning 4 × 500 mL Cleaning and conditioningFinal Rinse 1 × 500 mL deionized waterBeakers 2 × 250 mL plasticGloves 1 × pair glovesSyringe to provide a liquid streamBrush 1 × sensor cleaningInstruction sheet

Instructions for A1600054 pH ChemicalCleaning Kit

NOTE 1: A suitable place to do chemicalcleaning is at a counter or bench with alaboratory sink, with a chemical drainwhere waste is contained and treatedbefore release.

NOTE 2: IC Controls kits are kept smalland portable so that they can be taken toinstallation sites, together with a plasticbucket of water (for rinsing) and arag/towel (for wiping or drying). Wastematerials (particularly acid leftovers)should be returned to the laboratory sinkfor disposal.

CAUTION! use extra care when handlingcleaning solution as it contains acid. wearrubber gloves and adequate facialprotection when handling acid. Follow allP/N A1100091 & P/N A1100094 SDSsafety procedures.

a) Set up the cleaning supplies wherecleaning is to be performed. Lay out thesensor cleaning brush, syringe, cleaningsolutions and rinse solutions, plus thebeakers and sensor.NOTE: Ensure your cleaning solutionbeaker is on a firm flat surface since itwill contain acid.



SENSOR MAINTENANCE IC Controls

b) First remove the pH sensor from theprocess and examine it for deposits.Use the sensor cleaning brush and taprinse water to loosen and flush awayany deposits within the measurementarea. Detergent can be added to removeoil films and non-tenacious deposits.Hard scales and other tenacious depositsmay require chemical cleaning.

c) CHEMICAL CLEANING: Fill abeaker ¾ full of pH electrode washsolution P/N A1100091.

d) Lower the pH sensor into the center ofthe beaker until the entire tip issubmerged.

e) Keep removing, re-immersing the pHsensor until the pH electrode andreference junction appear clean.Stubborn deposits can be removed withthe brush and syringe to squirt washsolution into hard to reach areas.CAUTION! Use great care whenbrushing and squirting acid. Wearrubber gloves and facial protection.

f) Rinse the cleaned sensor thoroughly intap water and then with deionized waterin the syringe for a second rinse prior tocalibration.

g) Check the sensor against a pH buffernear the application pH. If the sensor isstill not reading properly (± 0.5 pH) inthe buffer, re-clean using gentle scaleremover, P/N A1100094, steps h) to l).

h) CHEMICAL DESCALING: Fill abeaker ¾ full with gentle scale remover,P/N A1100094.

i) Lower the pH sensor into the center ofthe beaker until the entire tip issubmerged.

j) Keep removing, re-immersing the pH

sensor until the pH electrode andreference junction appear clean.Stubborn deposits can be removed withthe brush and syringe to squirt scaleremover into hard to reach areas.CAUTION! Use great care whenbrushing and squirting acid. Wearrubber gloves and facial protection.

k) Rinse the cleaned sensor thoroughly intap water and then with deionized waterin the syringe for a second rinse beforecalibrating.

l) Check the sensor against a pH buffersolution near the application pH.

m)A clean and rinsed pH sensor shouldread near 7 in pH 7 buffer. If it doesnot, troubleshoot the pH sensor, wiringand analyzer, and/or proceed toRestoring Electrode Response.

Available Supplies:A1100090 pH storage solution -6P=6 pack

A1100091 pH wash solution -6P=6 pack

A1100092 pH renew solution -6P=6 pack

A1100094 scale remover -6P=6 pack

A1100192 deionized water -6P=6 pack

A1100228 anti-coat for pH, 100 mL

A7400020 poly beaker

A7400031 10 mL syringe

A1100016 sensor cleaning brush

A1600050 pH calibration kit

A1100051 pH 4 buffer; red -6P=6 pack

A1100052 pH 7 buffer; green -6P=6 pack

A1100053 pH 10 buffer; blue -6P=6 pack

A1600334 NIST traceable certificates


IC Controls pH SENSOR TROUBLESHOOTING

pH SENSOR TROUBLESHOOTINGIn order to troubleshoot a pH sensor, it isvery important to be certain that theanalyzer used for troubleshooting isfunctioning correctly.

Before testing the pH sensor, be sure thetest analyzer is known to be good.

FIRST: Inspect electrodes and if dirty orscaled:

Clean with a soft cloth.

Acid clean to remove scale as perChemical Clean procedure.

SECOND: Run buffer tests in (but do notadjust analyzer):

pH 7 buffer; write down reading andresponse time

pH 4 buffer; write down reading andresponse time

Slow response? Clean again or acid cleanovernight in electrode wash solution,A1100091. Make sure that after cleaningresponse is not longer than 3 minutes.

REFERENCE: If pH 7 reads between6 pH and 8 pH then reference is good. IfpH reading outside pH 6 or pH 8, thenreference is poor or has failed.

pH GLASS: Subtract pH 4 reading frompH 7 reading.

if result is 2.5 to 3, the glass is good.

if result is less than 2.5, then pHelectrode is failing and should bereplaced.

Less-responsive pH electrodes cansometimes be regenerated with A1100092

electrode renew solution. Refer toRestoring Electrode Response.

THIRD: If pH sensor passes tests, then itis good.

Place electrode back in the loop and thenrun a 2 buffer calibration following theinstructions in this manual.

FOURTH: If the sensor fails tests:

Replace the pH sensor.

Consider returning sensor toIC Controls for failure analysis ifelectrode life seems short.

IC Controls offers a free electrode andapplication analysis that may help increaseelectrode life in your application. Exampleof analysis: Slow Response – typicallydue to excessive sample line length andlow flow, thus producing long sampletransport time to the pH sensor from thesample point. Resolve by adding a fast-flow loop with the sensor in a short sidestream, or by shortening the line.

Slow response can also be caused by abuildup of dirt in the sample line. In thiscase the problem could be alleviated bychanging the sample point or by installinga dirt settling pot.



pH SENSOR TROUBLESHOOTING IC Controls

Troubleshooting Tips for pH

Reading spike – characteristic of bubblesin the sample line passing through thesensor or sticking to the pH sensor. Alsocharacteristic of pickup from interferencepulses generated from AC lines, when ACloads go off-line.

Readings gradually drifting away – thepH sensor can no longer be calibrated.This problem is typical of scale orsludge/slime deposits on the pH glass. Thesensor may need to be cleaned.

Readings at maximum; under allconditions − either the sensor is in air orthere is a problem with the wiring/analyzersetup. Test for shorts by disconnectingBNC and checking impedance betweencenter pin and outside housing with sensorin air. Insulation value should exceed100 MΩ.If the sensor is OK then use the model 659portable calibrator/analyzer to test thepreamp, wiring and the analyzer. If theproblem persists with the 659 in place thenit is an analyzer problem.

If the sensor tests as still good, and theanalyzer and wiring works with the 659,but the “+ERR” or over-scale still occurwhen the analyzer and sensor are hookedup and placed in service, then the mostlikely cause is a ground loop shortforming, not actually a pH sensor problem.Refer to the 659 instruction manual troubletesting procedures to resolve this pH loopplant site interaction problem.

The above symptoms cover mostdifficulties associated with pH sensors.The key to isolating problems in the pHsensor or analyzer is being able to separatethe two.

Restoring Electrode Response

Used electrodes which are mechanicallyintact but low efficiency or slowresponding, can often be restored to fullresponse by one of the followingprocedures:

1) SCALE DEPOSITS:Dissolve the deposit by immersion ofthe electrode tip, overnight (or overweekend), in electrode wash solution, P/N A1100091, followed by rinse in tapwater. Soak in electrode storagesolution, P/N A1100090 for 1 to 2hours.Difficult cases: Repeat substitutinggentle scale remover, P/N A1100093,then 15 minute rinse.

2) OIL OR GREASE FILMS:Wash electrode tip with detergent andwater. If film is known to be soluble ina particular organic solvent, wash withthis solvent. Rinse electrode tip withtap water. Let sit in deionized water, P/N A1100015, for 2 to 4 hours, followedby 2 to 4 hours in electrode storagesolution, P/N A1100090.Difficult cases: Repeat using wash inSodium hypochlorite (Javex Bleach) inwater solution, adjusted to pH 6.5 ± 0.5with vinegar or acid.

3) PLUGGED OR DRY REFERENCEJUNCTION:Remove the contaminant with one ofthe above procedures, then soak inelectrode storage solution, P/N A1100090 for 24 hours to one week.


IC Controls pH SENSOR TROUBLESHOOTING

Difficult cases: Repeat but heat almostto boiling for ½ hour first, then soak inelectrode storage solution, P/N A1100090 for 24 hours to one week.

4) BIOLOGICAL GROWTHS:Wash electrode tip with detergent andwater.Difficult cases: Wash with Sodiumhypochlorite (Javex Bleach) in watersolution, adjusted to pH 6.5 ± 0.5 withvinegar or acid. Use rubber gloves, andwash until deposits fall off or turnwhite. Rinse tip with tap water. Let sitin deionized water, P/N A1100015 for 2to 4 hours, then 2 to 4 hours in electrodestorage solution, P/N A1100090.

5) Clean, but slow and less than 85%efficiency:

Wash electrode tip with electrode renewsolution, P/N A1100092, for15 minutes. Rinse electrode tip usingtap water for 15 minutes. Let sit indeionized water, P/N A1100015, for 2to 4 hours, followed by 2 to 4 hours inelectrode storage solution, P/N A1100090.

NOTE: If none of the above proceduressucceed in restoring electrode response, itis near the end of the useful life of thatsensor and should be replaced.



GLOSSARY IC Controls

GLOSSARYElectrode Both a pH sensing electrode and a reference electrode are needed for theanalyzer to measure the process. Commonly these are combined and referred to as a pHsensor, or a combination electrode (or combo). The temperature sensor may be built intothe electrode as well.

Nernst Equation Equation which relates the voltage signal produced by theelectrodes to the pH of the sample. The equation is temperature dependent.

pH The negative logarithm of the hydrogen ion concentration in solution.

pH Glass Electrode A glass of special composition can be made to respond to pH. Inorder to mount the pH glass , a glass shaft is needed. The pH responsive glass mountedon the end of a glass shaft is called a glass pH electrode, or pH sensing electrode. Both asensing and a reference electrode are needed to measure pH.

pH Sensor Contains both a pH sensing and a reference electrode needed to measurethe pH. Also referred to as a pH electrode (or combination electrode). The temperaturesensor may be built into the electrode as well.

Reference Electrode A reference electrode generates a known voltage when comparedto the Standard Hydrogen Electrode in solution, while also making an electricalconnection to the liquid. The reference electrode provides a second connection to theliquid so the pH responsive voltage of the glass electrode can then be measured. Itsknown voltage is then subtracted resulting in just the voltage due to pH.

TC Temperature compensator.

Temperature Compensation Nernstian correction for the influence oftemperature on the pH electrode. The analyzer reads out pH as if the process were at25 ° C or 77 °F, regardless of actual solution temperature.

Page38 www.iccontrols.com um-600-sensor-r6


IC Controls DRAWINGS

DRAWINGS

D5160327: Generic pH Sensor Wiring Diagram


IC Controls DRAWINGS

D4850015: pH Interface


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