Differential pH ProbeType 18

Operating Instructions

384-5 e

Contents

1 Introduction1.1 Glass testing2 Measuring principle2.1 Model applications3 Technical data4 Handling information for

the glasslined pH probe5 Storage and installation5.1 Storage5.2 Installation6 Connection of pH transmitters6.1 Parameter setting6.2 Calibration7 Cleaning/Sterilization7.1 Admissible CIP cleaning processes7.2 Sterilization methods8 Maintenance9 Spare parts

Differential pH Probe Type 18

1 IntroductionThe differential pH probe type 18 supplies a product-specific signal which may be called a relative pH. This relative pH may be used for controlling and monitoring uniform processes.

m 1.1 Glass testingDuring a spark test, inflammable sparks may occur at the pores in the form of an electric arc. There-fore, spark testing may only be car-ried out outside of potentially ex-plosive atmospheres.

The customary high-voltage spark test of the glass lined surface is not permitted for the measuring probes!

Before performing a high-voltage spark test on the reactor, the probe must be protected against damage by electrical or mechanical influ-ences. The entire glass lining of the probes can be monitored using the Pfaudler glass testing equipment of the types Corrosion Detector (port-able) or GlasSparker®. When moni-toring a reactor with one of these glass testers, the integrated probes are also monitored automatically.

Depending on the conductivity of the product, the accuracy of the measurement is influenced by a glass tester. For this reason, it must be ensured that the measurement and glass testing functions do not operate at the same time. Glass monitoring must be switched off during measurement.

2 Measuring principleConstruction of the enamel coated probe is based on a rigid steel rod. A blue base enamel is overlaid with two yellow bands of ion sensitive enamel. The measuring electrode is sensitive to H ions. The ref-erence electrode supplies a potential that depends on the dissolved salts. The stability of the reference enamel poten-tial increases with the salt buffering of the product. The potential is used as a reference value for the pH measuring electrode.

Both measuring electrodes are stable in the long term and are not subject to age-ing. Therefore it is possible to program the probe for a product or a control point by determining and specifying a slope value. The measuring probes can be cleaned and sterilized in-line using the normal CIP methods (cf. section 7.1). The highest reproducibility of the meas-ured values is achieved by wet steam sterilization after alkali and acid cleaning (cf. Figure 6).

The probe can be directly connected to pH measuring units with symmetrical highresistance inputs. They must offer the possibility of setting the zero point and the slope in a range between 7-14 pH and 50-59 mV/pH and the isothermal voltage to a max. of +400 mV or 3.0 pH.

Automatic temperature compensation with the built-in Pt 1000 is only possible if the pH transmitter is equipped with Uis compensation.

2 © Pfaudler GmbH

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45

6

1 steelbody2 enamelpHmeasuringelectrode3 enamelreferenceelectrode4 Pt1000temperatureprobe

5 metalpotentialconduction6 groundingofproduct(stainlesssteeladapter)7 processpHmeterwithsymmetricalinputs8 standardizedpHoutput

mV/Ref.+rH

mV/pH+rH

Figure1 Blockdiagram Figure2 pHprobetype18+cable

Differential pH Probe Type 18

In contrast to pH probes with a constant reference system and absolute pH meas-urement, differential pH probes supply pH values measured in relation to a pro-ductdependent reference value – thus providing a “relative pH”.

Since many processes are known to pro-ceed always in the same manner, the reference value for a certain process becomes a constant value. Thus, the “relative pH” is the real pH.

Most processes in the chemical industry, the pharmaceutical industry and in the food processing sector are repetitive manufacturing processes performed according to the same schematic. They require a certain pH which is obtained in open or closed-loop control in order to achieve a homogeneous product quality.

2.1 Model applications■■ Fermentation■■ Continuous reactions■■ Production of dairy products■■ Product monitoring■■ Measurement in water-free product■■ Measurement with high gas pressure■■ Measurement in food production

3 Technical data

Measuring range Operating temperature Operating pressure Measuring chain zero Slope Temperature compensation Thermal shock resistance

Transmitter requirementsInputs Zero point Uis compensation Temperature compensation

pH 3 to pH 12-5 to +140 °C (higher temperatures on demand)15 bar, no pressure compensationpH 7 to pH 14 (product-dependent)min. 50 mV/pH at 25 °Cwith Pt 1000 resistance thermometermax. 130 °C

2 symmetrical high-resistance inputs > 1 x 1012 Ω selectable between pH 0 and pH 14between –500 and +500 V or for ISpH 3with Pt 1000 resistance thermometer

3© Pfaudler GmbH

lowbuffering

mediumbuffering

Applicationareadependingonthesaltbufferingoftheenamelreferencesensor

strongbuffering

141312111098

actualpHvalue76543210

1 2 3 4 5 6 7 8 9 10 11 12 13 14setpHvalue

corrosionpossible

corrosionpossible

functiondependingonthesaltbufferingofthereference

enamel

functiondependingonthesaltbufferingofthereference

enamelapplicationarea

Figure3 Applicationrangeofthedifferentialphprobe

Figure4 Dimensionoftype18

1 2 3 4 5

145 60 73

1 glassreferenceelectrode2 glasspHmeasuringelectrode3 groundingofproduct(stainlesssteeladapter)

4 unionnut5 plug-inconnection

Differential pH Probe Type 18

4 Handling information for the glasslined pH probe

The differential pH probes are pressure and thermal shock resistant due to the hotmelt steel and glass compound. The probes have a very high mechanical sta-bility and are extremely robust.

m Inappropriate handling, e.g. hitting and scratching the probe on steel, ceramics, glass or stone may cause damage to the probe. Depend-ing on the scope of the damage, the probe may not fail immediately but rather when the temperature changes. If a defective measuring probe remains in aqueous solutions for prolonged periods of time, the glasslining may flake.

m When using a transmitter with impedance monitoring which indicates such a damage, the meas-uring probe must be immediately removed (within 24 h) after an alarm message to avoid flaking of the glasslining.

5 Storage and installation

5.1 StorageThe differential pH probes can be stored dry for an indefinite period of time at tem-peratures between –30 ... +80 °C in their packaging. After prolonged storage, the probe has a stable potential after simple steam sterilization.

If no steam sterilization is carried out, the probe should be wetted in standard buffer solution pH 7 for 24 h prior to in-stallation. Without wetting, the maximum zero point drift of a probe is approx. ± 0.2 pH until a stable potential is reached. Recalibration should be performed after 24 h.

5.2 InstallationProcedure:■▼ Remove the probe from the packag-ing, remove the protective plastichose and carefully introduce the probeinto the nozzle.■▼ Fasten probe with union nut.

■▼ Connect cable. For this purpose,loosen the heavy gauge conduit con-nection at the protective plastic cover,push out the connector, put the con-nector in the proper position, andfirmly press it into the female connec-tor of the probe (water-tight inter-lock). Push the protective cover andO-ring sealing onto the probe until thestop, and tighten the heavy gaugeconduit connection again manually.■▼ The cable (blue color) must be fastenedvibration-free. The cable must not belaid together with power cables.

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# Cable color Assignment

1 white glasspHprobe (coaxialcabel)

2 brown glassreferenceprobe (coaxialcabel)

3 brown Pt1000

4 green Pt1000

5 blue groundingofproduct (stainlesssteeladapter)

6 black Pt1000

cabelshield (groundcontactovertheplug)

8 violet coaxialshield1 (insulatedonplug)

9 orange coaxialshield2 (insulatedonplug)

Figure5 Assignmentofconnectioncable

Differential pH Probe Type 18

6 Connection of pH transmitters Only suitable transmitters with symmetri-cal high-resistance inputs may be used.

For programming the transmitters, please refer to the manufacturers’ oper-ating instructions.

Please note:For as long as the probe is connected to the transmitter, the voltage sup-ply of the transmitter may be dis-connected for prolonged periods of time (more than two days) only if the probe is standing dry. Otherwise, a polarization of the electrodes (zero point shift) may occur.

5© Pfaudler GmbH

6.1 Parameter settingDepending on the transmitter used, various parameters have to be input before the differential pH probe may be used:

1. Display =pH

2. Measuringtemperature =Pt1000

3. Calibr.measuringtemperature =Pt1000

4. Temp.correction =No

5. pH-currentoutput ?1

6. (Temp.currentoutput) ?1 (onlyfor2ndcurrentoutput))

7. Nominalzero =10,0pH (onlyforKnickequipment)

8. Nominalslope =52,5mV/pH (onlyforKnickequipment)

9. Calibrationmode =pH (onlyforKnick71Xequipment)

10. Impedancemeas.pHelectrode =On (min.=0,5MΩ/max.=1000MΩ)

11. Impedancemeas.ref.electrode =On (min.=0,5MΩ/max.=1000MΩ)

12. Removebothjumpersforimpedancemeasurement(HighImpedance)onlyforYokogawaEXAPH-202

13. BothjumpersonHighImpedanceslots.OnlyforYokogawaEXAPH-402

14. InputofIspH3.0forYokogawaequipmentinServiceCode

15. Inputof95%slope(withoutsterilization)forYokogawaequipmentinServiceCode

16. Inputof90%slope(withsterilization)forYokogawaequipmentinServiceCode

17. InputinDatacal.fieldforKnickequipment.TakeZeropoint,Slope,andUISmVvaluefromthePfaudlermeasuringlog.

18. InputinSensordatafieldforSiemensequipment.TakeZeropoint,Slope,andUISmVvaluefromthePfaudlermeasuringlogandsetIS-pH=3.0

1Customervalue

Differential pH Probe Type 18

6.2 CalibrationThe differential pH measuring probe cannot be calibrated with buffer solutions but must be programmed for an application. For batch processes or continuous reactions, it is programmed for the desired final pH or the normal pH. In other words, install the probe, start the process, take samples (measurement in the laboratory or with a manual unit) and calibrate the measurement at the desired pH level by means of sample calibration (single-point calibration). Re-calibration is usually not necessary if the probe had been well formed.

Of course, it is also possible to perform a two-point calibration when the probe is removed. Two product samples are re-quired for this purpose, i.e. a start prod-uct and an end product. Measure the pH of both samples in the laboratory, per-form a buffer calibration, and enter the measured pH values as buffer values. This process yields a product-specific zero point and the slope. Once these val-ues have been determined, the zero point and slope will normally always be reproducible for the probe and product in question.

7 Cleaning/SterilizationThe probe can be cleaned/sterilized inside the reactor. For CIP cleaning it must be ensured that the admissible alkali and acid concentrations as well as the maxi-mum temperature or cleaning time are not exceeded. Otherwise, the glasslining of the electrode would be subject to increased corrosion.

Please note: With alkali cleaning, corro-sion is doubled with every temperature jump of 10 °C. The use of oxidizing acids, such as HNO3, is limited to solutions of 1.5 % at a maximum of 60 °C.

7.1 Admissible CIP cleaning processes

■■ 1.5-2 % alkaline solution, max. 85 °C,max. 1 h

■■ 1.5 % acid (HNO3), 60 °C, max. 15 min.■■ Steam 134 °C, max. 2 h.

Depending on the CIP cleaning process used, compensation of the measured value shift may take up to 12 hours. Forming of the differential pH probe will eliminate this measured value shift more readily – cf. Figure 6.

6 © Pfaudler GmbH

saturatedsteam135°C

steam100°C

water95°C

water80°C

water25°C

0,1

DeltapH0

–0,1

–0,2

–0,3

–0,4

–0,5

Afterthecleaningwith2%NaOH(30minat85°C)

Timeofregenerationapprox.12h

0 10 20 30 40 50 60 70 80Timeofregeneration(min)

Figure6 ProbeformingafterCIPcleaning

Differential pH Probe Type 18

8 MaintenanceThe differential pH probe does not require any maintenance works. It is possible to check the probe in the “buffer calibra-tion” measuring mode using standard buffer solutions pH 7 and pH 10 (Titrisol buffer, Merck).

For cleaning or removal of residues, con-centrated acids may be used for a short time at room temperature only – e. g. 5 % HCl, 15 min, 20-30 °C. Decalcifica-tion may be performed with commercially available antiliming agents. Tenacious residues may be removed with a cleaning milk for ceran cooking plates – do not use any metallic or abrasive sub-stances!

7© Pfaudler GmbH

9 Ersatzteile

# Designation Part no.

1 0-ringmadeofEPDMforsteriledesign,23,4x3,5mm 024365D

1 0-ringmadeofEPDMforflangedesign,32,5x3,6mm K03246–

2 0-ringmadeofvitonforprotectivecap,25x1,5mm 024336D

3 Blueconnectioncable,2mwithconnector 2546342

3 Blueconnectioncable,5mwithconnector 2546345

3 Blueconnectioncable,10mwithconnector 2546340

4 UnionnutR11/4"forsteriledesign 032126–

1 4 2 3

Figure7 Spareparts

The information provided in this documentation corresponds

to the state of the art at the time of printing. It is published

in good faith. However, we will accept no warranty claims

based on the information provided in this documentation. We

reserve the right to include improvements, amendments and

new findings in this documentation without prior notice. The

actual design of products may deviate from the information

contained in the calatoge if technical alterations and product

improvements so require. The proposal made by Pfaudler for

a concrete application will be binding in such cases.

The present documentation is made available free of charge

to our customers and other interested parties. The right to

print or copy this documentation, or any parts there of, or to

convert the same into electronic form shall be subject to our

written permission.

All rights reserved by us.

Pfaudler GmbH

P.O. Box 1780 D-68721 Schwetzingen

Pfaudlerstraße D-68723 Schwetzingen

Phone +49 6202 85-233

Telefax +49 6202 85-273

E-mail info@pfaudler-instrumentation.com

www.pfaudler-instrumentation.com