641-3e

R O B U S T .

A N D S E N S I T I V E .

ANALYTICAL

MEASUREMENT

TECHNOLOGY

FROM PFAUDLER

E V E R Y T H I N G U N D E R C O N T R O L

W I T H P F A U D L E R :

2

The Pfaudler measuring probes.Simple - but tough.In many processes, things can get rough - a problem for most sensors. When othermeasuring systems have long ceased towork (with all the unpleasant consequencesyou know only too well), our measuring pro-bes are still going strong. They deliver fault-less and precise test readings whereverthey are used - whatever the conditions.

A strong combination:Enamelled steelWhat makes Pfaudler measuring probes so different? Answer: We use enamelledsteel. This makes light work of resistingattack, physical or chemical, and goes ondoing so for a long time.

The steel makes our measuring probesimpervious to physical influences such ashigh flow rates in reactors and pipes, sud-den pressure surges and pressures up to100 bar.

The Pfaudler enamel used, along with thepH enamel, provide the measuring probeswith an effective protective shield againstattack by chemicals. The enamel remainsabsolutely neutral during the process withno catalytic or biological effects.

Where others give up, our measuringprobes keep on going. The technologyemployed is robust making processmonitoring possible for the first time inmany areas. Pfaudler enamel is knownall over the world for its tremendouschemical resistance.

O U R P H , R H A N D L F

M E A S U R I N G P R O B E S

Robust -but precise and very, very sensitivePfaudler measuring probes are as sensitivein delivering measured values as they arerobust in use. You can rely on this vitally-important sensitivity. Every time.

Positiones “where the action is”Our measuring probes work where it reallyhappens. That means right inside the reac-tor or in the main flow line, permitting mea-surements that are direct, precise andimmediate.

After all, why should your measuring becomplicated when it can be so simple? Ourmeasuring probes don’t need pumps, shut-off devices and by-pass pipes. And there’sa bonus: you save money and gain onsafety.

With precise and immediate test rea-dings at your fingertips, you can reactswiftly and raise your product quality.End result: you’ve made savings allround.

Fit it - then forget it for a long timeIt isn’t just the material that was chosen for a long life. A lot of thought went into the design, too. We wanted measuring probes which would have a wider range of uses than had previously been the caseand which would increase productivity.

Their direct and problem-free location inthe midst of a turbulent process, togetherwith the smooth enamel surface of themeasuring probes, prevents product depo-sition. The probes are thus self-cleaning.Measurement errors are prevented, whilecostly and time-consuming cleaning pro-cesses are a thing of the past.

Service intervals:Often a whole yearInfrequent servicing means continuous production, raised plant productivity and a saving on expensive service downtime -all in all, greater economy in product manufacture.

There’s a completely different but equallyimportant consideration, too: having tointerrupt hard-earned leisure time at theweekend because of operating faults ismore than a nuisance to all concerned. Our robust, sensitive measuring probes are worth investing in - in every way.

You install them and forget about themfor a long time. That’s what we callreliability.

STRENGTH AND

SENSITIVITY, THE

COMBINATION OF

APPARENT CONTRASTS

MADE POSSIBLE BY

ENAMELLED STEEL

TECHNOLOGY

FROM PFAUDLER

200

160

120

80

40

2 4 6 8 10 12 pH

0,1

0

°C

P F A U D L E R

P H - M E A S U R I N G P R E C I S I O N

L1

L

dia.

Chemical attacksIt’s mainly thanks to the materials we usethat virtually nothing affects our measuringprobes. The probe carrier is protected byPfaudler enamel - extremely resistant tocorrosion.

Vital for the resistance of the measuringprobes as a whole is the yellow pH enamelof the measuring electrodes. The diagramon the right shows the resistance of thisenamel at given temperatures to acids,water and alkalis. The isocorrosion curve0.1 mm/year constitutes the limit of theguarantee. The corrosion curve for the pHenamel was determined gravimetrically. In

practice, deviating values can occur as aresult of changed product

volume/

ConsistencyPotential constant and consistency remainwithin a measurement accuracy of ±0.1 pH,even after operating intermissions. It is not necessary to dismantle the measuringprobes. They can be stored dry.

Time taken to register pH changesThe Pfaudler pH measuring probes com-bine speed and robustness. pH changesare registered within seconds where and asthey occur.

Electrical resistanceThe resistance of the measuring electrodeis max. 1,000 MΩ.

Isocorrosion curve of pH enamel(Mean values)

enamelled surface proportions. Like glass,enamel is not resistant to fluoride.

Temperature compensationA built-in resistance thermometer, togetherwith the transmitter, delivers a precise pHvalue at any temperature.

resistant

not resistant

corr

osio

n ra

te (m

m/y

ear)

F R O M A P U R E L Y

T E C H N I C A L V I E W P O I N T . . .

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ElectrolyteOur absolute instrumentation measuringprobes operate with Pfaudler electrolyte.This is based on KCl or K2SO4.

Within the permissible pressure difference,max. leakage is 5 ml/h. At an overpressureof 1 bar, approx. 0.2 ml/h should be anticipated. This means barely 1 litre ofelectrolyte in six months of continuous use.Measuring probe and reservoir vesseltogether hold approx. 1.7 litres (N version)or 0.7 litre (K version).

Electrode slopeThe enamel electrode guarantees values ofmore than 55 mV/pH at 25 °C. The effec-tive value is documented in the test report.

Chain zero-pointThe measuring chain zero-point of the ena-mel electrode in combination with thePfaudler silver acetate reference electrodetype AgAGel is pH 1.35 ± 1 and in combi-nation with the silver-silver chloride refe-rence electrode type AgAgCI is pH 8,65 ± 1.

TemperatureThe limits are dependent on electrode resi-stance, chemical resistance of the pH ena-mel and electrolyte vapour pressure.The permissible range lies between 0 and140 °C. Below 0 °C the pH display is slug-gish. However, the measuring probe canstay in the reactor down to -5 °C and withspecial electrolyte down to -30 °C.

PressureThe measuring probes may be used withinthe range -1 to +9 bar. Special versionsoperate in process pressures up to 16 bar.

It is sufficient to set the probe once inaccordance with the highest pressureoccurring during the process. In the eventof sudden pressure-drop in the reactor ves-sel, function and operational safety areunaffected. No pressure compensation isnecessary.

The pressure inside the reservoir vesselmust be at least 1 bar above the maximumoperating pressure. This ensures that thediaphragm is filled with electrolyte and pre-vents penetration by the product. Range and accuracy of measurement

The linear range of the characteristic curveis from pH 0 to pH 10 at 25 °C. Measure-ment is accurate to below ± 0.1 pH.

Measurements up to pH 12 are briefly pos-sible. In this region, alkali error results in adeviation of more than 0.1 pH. This risesas the pH value increases.

pH

Measurement principle of Pfaudlermeasuring probes for absolute pH value determination

160

120

80

40

2 4 6 8 10 pH

°C

0

Range of application with measurementaccuracy < ± 0.1 pH at 0.1 nNa+

Range of application

P H M E A S U R I N G P R O B E S

T Y P E S 0 3 / 0 4 . . .

The reference electrode is located in theeletrolyte vessel. It is in contact with theproduct to be monitored via the electrolyteand a ground diaphragm. An isolationamplifier is connected downstream of themeasuring and reference electrode. Mostof commercially-available pH transmittercan be connected to the isolation amplifier.

The enamel measuring electrode isdirectly connected to its metal lead, thuseliminating the weak point at the inner buf-fer/by-pass electrode interface. The pHenamel is in contact with liquid on one sideonly, unlike the conventional glass electro-des.

The reference electrode is located sepa-rately from the measuring electrode in anelectrolyte vessel. The pressure in the elec-trolyte system is greater than the operatingpressure in the reaction chamber. Productpenetration through the diaphragm and viathe long electrolyte line is not possible. Thereference electrode is thus protected fromany contamination.

Putting together the pH measuring probes The modular design of the Pfaudler pHmeasuring probes means that you canassemble your own measuring probe tosuit your operating conditions:■ two different electrolyte vessels: version K is compactly mounted on thehead of the measuring probe, while version N is separate from the probe andconnected to it via a flexible hose.■ two different diaphragms: in type 03,this is a shrink-fitted glass disc, in type 04 itconsists of two surfaces screwed together.

The compact type 04 K, with electro-lyte vessel mounted on the probe head

Design and measuring principleA measuring electrode of pH-sensitive ena-mel, together with a reference electrode,make up the pH measuring probe.The mea-suring electrode fits round the lower end ofthe enamelled steel tube. The electrodehas a large surface area and covers thewhole of the lower end of the measuringprobe. It is directly exposed to the productflow, without a protective cage or any simi-lar device, and thus gives a direct andimmediate pH reading.

6

The pH measuring probe with twomeasuring systemsFitting two identical pH measuring systemson one probe carrier means that self-moni-toring through comparative measurementis possible.Technical data are otherwise as for type 03or type 04.

Doubly sure: the Pfaudler pH measu-ring probe with two measuring systems

Takes up very little space: the Pfaudlerring pH probe for measurement in thepipeline

The ring ph measuring probeThis version can be installed directly inpipelines. The smallest nominal size is DN 50. The enamel measuring electrodeand the diaphragm are on the inside surface of an enamelled ring. Technicaldata are as for type 03, Version N.

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. . . A N D T H E I R

” C L O S E R E L A T I O N S “

D I F F E R E N T I A L P H M E A S U R I N G P R O B E S T Y P E 1 8/4 0

T H E N E W W A Y T O M O N I T O R P H

8

The measuring principleTwo separate ion-sensitive enamel electro-des are fused on to the end of the enamelprobe carrier. In the zone pH 0 to 10, thepH enamel electrode responds to H+ ionsonly. The reference electrode delivers apotential which is dependent on the con-centration of dissolved salts and/or theproduct buffering. In type 40 a rhodiumcentral electrode embedded in the enamelserves to earth the product which is to bemeasured. Reference electrode, diaphragmand electrolyte line are not necessary. Aresistance thermometer is built into themeasuring probes to provide temperaturecompensation for pH value.

Compact design:The pH measuring probe type 18

Complex function, simple design:The pH measuring probe type 40

In which processes can relative measurement be used?Relative measurement is ideal for proces-ses which are constantly repeated in thesame format - e.g. continuous reactions(neutralisation), biotechnical processes andfermentation. It is also suited to high-purityprocesses in which the presence of electro-lyte fluid is undesirable.

Are there any further advantages?Well, of course enamelled steel is impor-tant here, too. The measuring probes areresistant to chemical and physical attacks.They are very compact, take up little spaceand can therefore be built into reactors andpipelines wherever desired.No servicing is necessary and the function principle means that the measuring probes are highly reliable.

Relative simplicity:Relative instead of absolute pH measurementsUnlike the pH measuring probes with con-stant reference system and absolute pHmeasurement, the differential pH probesdeliver pH values which are measured to aproduct-dependent reference quantity -hence “relative pH”.

Since there are many known processesand all follow the same course, the refe-rence quantity for a given process beco-mes the constant. This means that the“relative pH” is the real pH value.

Most processes in the chemical, pharma-ceutical and food industries are repetitivemanufacturing processes and run accor-ding to the same schematic. They are regu-lated or controlled to a set pH value inorder to ensure consistency of quality.In processes such as these, our type 18/40measuring probes are the right - and eco-nomically-sensible - choice. Their safe func-tioning principle, simple handling androbust construction, designed for uncompli-cated long-term use, make an importantcontribution to safe and economical pro-duction.

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SENSITIVE PH

MONITORING

FIRMLY IN CONTROL,

THE DIFFERENTIAL

PH MEASURING

PROBE TYPE 40

TYPE 18,

THE COMPACT

ENAMELLED STEEL

DIFFERENTIAL

PH PROBE

T H E R H A N D P H / R H

M E A S U R I N G P R O B E S

10

The Pfaudler rH measuring probesSeveral variants of our probes are desig-ned for measuring redox potential. Likeother Pfaudler measuring probes, theseare robust and resistant to attack. Theirfunction is to measure the redox potentialarising in oxidation or reduction processes.This measurement is carried out with anoble metal electrode against a referenceelectrode. There are two different versionsto choose from:

The rH measuring probe type A

rH

rH

pH

rH

The rH measuring probe type B

The combined pH/rH measuringprobe

Operating principle

The rH measuring probe, type AIn the case of type A, the redox potential ismeasured between a rhodium electrodeembedded in the enamel and a pH enamelreference electrode. The magnitude of thepotential occurring at the reference elec-trode depends on the pH value of the pro-duct. Thus, a redox voltage is obtainedwhich is not dependent on the pH value.The rH measuring probe is chemically highly resistant: the measuring electrode ismade of rhodium, the reference electrodeof pH enamel.

The rH measuring probe, type BIn the case of type B, the redox potential ismeasured between a noble metal electrodeand an external reference electrode in theelectrolyte vessel. The reference electrodeis connected with the product via an elec-trolyte line and a screw type diaphragm (aswith pH measuring probe type 04 or type03). Through the constant reference poten-tial, the measured redox voltage changeswith changing pH value.

The combined measuring probe pH/rHThe combination of both measuringsystems on one carrying tube makes possi-ble the simultaneous measurement of pHvalue and redox potential. The technicaldata for this combined measuring probeare as for the pH measuring probe type 03or type 04 and rH type B.

rH type A

rH type B

pH/rH

Type pH 03/04 pH 03/04 Dual pH Ring pH 40 pH 18

Measured value absolute pH 2 x absolute pH absolute pH relative pH relative pH

Diaphragm + Diaphragm + Diaphragm +Reference system Reference Reference Reference Reference enamel Reference enamel

electrode electrode electrode

Measuring range 0 - 10 pH 0 - 10 pH 0 - 10 pH 3 - 12 pH 3 - 12 pH

Slope (mV/pH) > 55 > 55 > 55 50 - 57,5 50 - 57,5

Temperature (°C) 0 - 140 0 - 140 0 - 140 0 - 140 0 - 140

Temperaturecompensation

Pt 100 Pt 100 Pt 100 Pt 100 Pt 1000

Pressure (bar) -1 ... +9 -1 ... +9 -1 ... +9 -1 ... +40* -1 ... +15

Explosion protectionyes yes yes yes noII 1/2 G EEx ia IIB T6 or

II 2G EEx ia IIC T6

Dimensions- Diameter see p. 13 see p. 13 ≥ DN 50 see p. 13

ø 18 mm

- Lenght approx. 140 -190 mm

Type rH A rH B pH/rH LF LF ring

Measured value Redox potential Redox potentialAbsolute pH

conductivity conductivityand Redox potential

Diaphragm + Diaphragm +Reference system Reference enamel Reference Reference – –

electrode electrode

Measuring range0 - 10 pH 1 - 2000 mS/cm 1 µS/cm - 2 S/cm

-1200 ... +1500 mV -1200 ... +1500 mV -1200 ... +1500 mV

Slope (mV/pH) – – > 55 – –

Temperature (°C) 0 - 140 -5 - +160 0 - 140 -25 - +200 -25 - +200

Temperaturecompensation

– – Pt 100 Pt 100 Pt 100

Pressure (bar) -1 ... +40* -1 ... +9 -1 ... +9 -1 ... +40* -1 ... +100

Explosion protectionyes yes yes yes yesII 1/2 G EEx ia IIB T6 or

II 2G EEx ia IIC T6

Dimensions- Diameter see p. 13 see p. 13 see p. 13 see p. 13 ≥ DN 50- Length

*Pressure of up to 100 bar possible

T E C H N I C A L

D A T A

11

12

Which measuring probe for which vessel?This page shows you at a glance the typesand dimensions of the Pfaudler vessels cur-rently available. The probe sizes best sui-ted to them are shown in the yellow area ofthe table. For further information re measu-rements, see drawing below.

Vessel dimensions Probe dimensions

Type/ Nozzle Reducing flangeNominal volume Diameter D L DN Spacer block

DN x L1

AE 63 508 38 450 50 -AE 100 508 38 670 50 -AE 160 600 38 670 50 -AE 250 700 38 800 50 -AE 400 800 38 950 80 -AE 630 1000 83 1150 100 -AE 1000 1200 83 1400 100 -AE 1600 1400 83 1600 100 -AE 2500 1600 83 1800 100 -AE 4000 1800 83 2000 150 -AE 6300 2000 127 2500 150 -

BE 1600 1400 83 1600 100 -BE 2500 1600 83 1800 100 -BE 4000 1800 83 2000 150 -BE 6300 2000 127 2500 150 -BE 8000 2000 127 3000 150 -BE 8000 2200 127 2500 150 -BE 10000 2400 180 2700 200 -BE 12500 2400 180 3200 200 -BE 16000 2600 180 3200 200 -BE 16000 2800 180 3200 200 -BE 20000 2800 180 3200 200 -

CE 1600 1400 83 1400 100 -CE 2500 1600 83 1600 100 -CE 4000 1800 83 2000 150 -CE 6300 2000 127 2500 150 -CE 8000 2000 127 2850 150 -CE 8000 2200 127 2500 150 -CE 10000 2400 180 2700 200 -CE 12500 2400 180 2700 200 -CE 16000 2600 180 3200 200 -CE 16000 2800 180 3200 200 -CE 20000 2800 180 3200 200 -

DG 100 600 38 450 50 -DG 250 800 38 670 50 -DG 500 1000 38 670 50 -DG 800 1000 38 950 50 50/80 x 45 1)

E 1200 1200 83 1150 100 100 x 120E 2000 1400 83 1400 100 100 x 100E 3000 1600 83 1600 100 100 x 100E 4000 1800 83 1800 100 -E 6000 2000 83 2150 100 -E 8000 2000 83 2150 100 -E 12500 2400 127 3000 150 -E 16000 2600 180 3200 200 -E 20000 2700 180 3200 200 -

L 160 600 38 670 50 -

T 100 600 38 450 50 50 x 70 2)

T 200 800 38 450 50 - 2)

T 300 800 38 670 50 50 x 30 2)

T 500 1000 38 670 50 50 x 110 2)

T 800 1000 38 950 50 50/80 x 45 1) 2)

1) Reducing flange in special version2) oblique nozzle

dimensions in mm

V E S S E L S A N D M E A S U R I N G

P R O B E D I M E N S I O N S

13

The LF measuring probe

The measurement principle

CalibrationIt is possible to use transmitters whichthemselves determine the cell constant ofthe measuring probe where the conduc-tivity of the product or of the calibrationsolution is known.

+

U≈ i≈–

T H E C O N D U C T I V I T Y

M E A S U R I N G P R O B E T Y P E L F

Please see folding page

Probe designIn the LF measuring probe, four metal(rhodium) electrodes are aligned longitudi-nally and fused into the enamel coating ofthe probe carrier. Thermometer tubes,baffles or spacer rings may be used asprobe carriers.The cell constant is dependent on the geo-metry and location of the probe and cannotbe predetermined. For this reason, a four-wire circuit is used. A constant alternatingcurrent flows across the two outer electro-des and through the product. The resultantvoltage drop is sensed by the two innerelectrodes and transmitted to a high-impe-dance measuring transmitter.

E N A M E L

I S “ O U R “ M A T E R I A L

Agitator vessel that nothing can agi-tate! Enamelled by Pfaudler

Cryo-Lock© agitator system – every-thing revolves around safe mixing

All roads lead to Pfaudler when it’s amatter of using enamelled products inindustry. We are known all over the worldas the specialists in this material, as resi-stant as it is hygienic. Enamel is not aneasy material to process: not everyonehas the know-how, and experience andexpert advice are very important. Pfaudlercan offer both: we have worked with ena-mel for almost 100 years and have carriedout our own thorough, efficient research inthe interests of product advancement.What’s more, we manufacture enamel our-selves and use it in a comprehensiverange of apparatus and components. Inaddition to the measuring probes descri-bed in this brochure, we are able to supplythe following:

■ Agitated vesselsDIN and other agitated vessels with ena-melled surfaces, in different sizes from 4 to 40,000 litres capacity for differentoperating pressures and temperatures.■ Agitator drivesin different versions, also bottom drive.■ Cryo-Lock© agitator systemThe cost-saving agitator system: rapid,inexpensive assembly and increasedsafety. A wide range of agitator shapes isavailable for optimisation of your agitatorprocesses.

■ Quatro-PipeFour functions in one connection piece: baffle, dip pipe, sensor tube and samplingtube.■ Pumps, pipes and valves■ Enamelled columns and storage tanks

Quality and service - of course!Our organisation is certified in accordancewith the requirements of DIN/ISO 9001.Customers using our products every daycan be sure that our service team will be attheir side if needed, bringing enormousexperience and state-of-the-art knowledgeon every occasion. Further, you can call onPfaudler for any of the following services:■ Testing and servicing■ Replacement part service■ Re-enamelling and updating of older vessels■ Info-service: product information andapplications technology courses.

For more informations see the following brochures:642: Technical Information

Analytical-Measuring Probes181: pH Probe Reiner in Aseptic

Design180: pH Sensor in Flue Gas

Desulphurization Plants643: High Responsiveness and Low

Maintenance

641-3e05.07.20© by Robbins & Myers, Inc.Printed in Germany

Pfaudler Werke GmbHP.O. Box 1780 · D-68721 SchwetzingenPhone +49 6202 85-0Main Fax +49 6202 22412Fax Sales +49 6202 26151Internet www.pfaudler.deemail Sales sales@pfaudler.de

While every effort is made to ensure that the information given in this bulletin is accurate, due tocontinuing development in design, plant and methodsof manufacture, we reserve the right to offer equip-ment which may differ in detail from that described.