Differential ph Probe Type 18 Contents 1 Introduction 1.1 Glass testing 2 Measuring principle 2.1 Model applications 3 Technical data 4 Handling information for the glasslined ph probe 5 Storage and installation 5.1 Storage 5.2 Installation 6 Connection of ph transmitters 6.1 Parameter setting 6.2 Calibration 7 Cleaning/Sterilization 7.1 Admissible CIP cleaning processes 7.2 Sterilization methods 8 Maintenance 9 Spare parts Operating Instructions 384-5 e
6 mv/ref.+rh mv/ph+rh 1 2 7 3 8 5 4 1 steel body 2 enamel ph measuring electrode 3 enamel reference electrode 4 Pt 1000 temperature probe 5 metal potential conduction 6 grounding of product (stainless steel adapter) 7 process ph meter with symmetrical inputs 8 standardized ph output Figure 1 Block diagram Figure 2 ph probe type 18 + cable 1 Introduction The 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 testing During a spark test, inflammable sparks may occur at the pores in the form of an electric arc. Therefore, spark testing may only be carried out outside of potentially explosive 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 influences. The entire glass lining of the probes can be monitored using the Pfaudler glass testing equipment of the types Corrosion Detector (portable) or GlasSparker. When monitoring 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 principle Construction 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 reference electrode supplies a potential that depends on the dissolved salts. The stability of the reference enamel potential 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 ageing. 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 measured 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 U is compensation. 2 Pfaudler GmbH
14 13 12 11 10 9 8 actual ph value 7 6 5 4 3 2 1 0 corrosion possible function depending on the salt buffering of the reference enamel application area function depending on the salt buffering of the reference enamel corrosion possible 1 2 3 4 5 6 7 8 9 10 11 12 13 14 set ph value low buffering medium buffering strong buffering Application area depending on the salt buffering of the enamel reference sensor Figure 3 Application range of the differential ph probe In contrast to ph probes with a constant reference system and absolute ph measurement, differential ph probes supply ph values measured in relation to a productdependent reference value thus providing a relative ph. Since many processes are known to proceed 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 requirements Inputs Zero point U is compensation Temperature compensation ph 3 to ph 12-5 to +140 C (higher temperatures on demand) 15 bar, no pressure compensation ph 7 to ph 14 (product-dependent) min. 50 mv/ph at 25 C with Pt 1000 resistance thermometer max. 130 C 2 symmetrical high-resistance inputs > 1 x 10 12 Ω selectable between ph 0 and ph 14 between 500 and +500 V or for ISpH 3 with Pt 1000 resistance thermometer 1 2 3 4 5 145 60 73 1 glass reference electrode 2 glass ph measuring electrode 3 grounding of product (stainless steel adapter) 4 union nut 5 plug-in connection Figure 4 Dimension of type 18 Pfaudler GmbH 3
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 stability 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. Depending 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 measuring probe must be immediately removed (within 24 h) after an alarm message to avoid flaking of the glasslining. 5 Storage and installation 1 2 3 4 5 6 8 9 # Cable color Assignment 1 white glass ph probe (coaxial cabel) 2 brown glass reference probe (coaxial cabel) 3 brown Pt 1000 4 green Pt 1000 5 blue grounding of product (stainless steel adapter) 6 black Pt 1000 cabel shield (ground contact over the plug) 8 violet coaxial shield 1 (insulated on plug) 9 orange coaxial shield 2 (insulated on plug) Figure 5 Assignment of connection cable 5.1 Storage The differential ph probes can be stored dry for an indefinite period of time at temperatures 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 installation. 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 Installation Procedure: Remove the probe from the packaging, remove the protective plastic hose and carefully introduce the probe into the nozzle. Fasten probe with union nut. Connect cable. For this purpose, loosen the heavy gauge conduit connection at the protective plastic cover, push out the connector, put the connector in the proper position, and firmly press it into the female connector of the probe (water-tight interlock). Push the protective cover and O-ring sealing onto the probe until the stop, and tighten the heavy gauge conduit connection again manually. The cable (blue color) must be fastened vibration-free. The cable must not be laid together with power cables. 4 Pfaudler GmbH
6 Connection of ph transmitters Only suitable transmitters with symmetrical high-resistance inputs may be used. For programming the transmitters, please refer to the manufacturers operating instructions. Please note: For as long as the probe is connected to the transmitter, the voltage supply of the transmitter may be disconnected 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. 6.1 Parameter setting Depending on the transmitter used, various parameters have to be input before the differential ph probe may be used: 1. Display = ph 2. Measuring temperature = Pt 1000 3. Calibr. measuring temperature = Pt 1000 4. Temp. correction = No 5. ph-current output? 1 6. (Temp. current output)? 1 (only for 2 nd current output)) 7. Nominal zero = 10,0 ph (only for Knick equipment) 8. Nominal slope = 52,5 mv/ph (only for Knick equipment) 9. Calibration mode = ph (only for Knick 71X equipment) 10. Impedance meas. ph electrode = On (min. = 0,5 MΩ/max. = 1000 MΩ) 11. Impedance meas. ref. electrode = On (min. = 0,5 MΩ/max. = 1000 MΩ) 12. Remove both jumpers for impedance measurement (High Impedance) only for Yokogawa EXA PH-202 13. Both jumpers on High Impedance slots. Only for Yokogawa EXA PH-402 14. Input of IspH 3.0 for Yokogawa equipment in Service Code 15. Input of 95% slope (without sterilization) for Yokogawa equipment in Service Code 16. Input of 90% slope (with sterilization) for Yokogawa equipment in Service Code 17. Input in Data cal. field for Knick equipment. Take Zero point, Slope, and U IS mv value from the Pfaudler measuring log. 18. Input in Sensor data field for Siemens equipment. Take Zero point, Slope, and U IS mv value from the Pfaudler measuring log and set IS-pH = 3.0 1 Customer value Pfaudler GmbH 5
0,1 Delta ph 0 0,1 0,2 After the cleaning with 2 % NaOH (30 min at 85 C) Time of regeneration approx. 12h saturated steam 135 C steam 100 C water 95 C water 80 C water 25 C 0,3 0,4 0,5 0 10 20 30 40 50 60 70 80 Time of regeneration (min) Figure 6 Probe forming after CIP cleaning 6.2 Calibration The 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 required for this purpose, i.e. a start product and an end product. Measure the ph of both samples in the laboratory, perform 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 values have been determined, the zero point and slope will normally always be reproducible for the probe and product in question. 7 Cleaning/Sterilization The 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 maximum temperature or cleaning time are not exceeded. Otherwise, the glasslining of the electrode would be subject to increased corrosion. Please note: With alkali cleaning, corrosion is doubled with every temperature jump of 10 C. The use of oxidizing acids, such as HNO 3, 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 (HNO 3 ), 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
8 Maintenance The differential ph probe does not require any maintenance works. It is possible to check the probe in the buffer calibration measuring mode using standard buffer solutions ph 7 and ph 10 (Titrisol buffer, Merck). For cleaning or removal of residues, concentrated acids may be used for a short time at room temperature only e. g. 5 % HCl, 15 min, 20-30 C. Decalcification 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 substances! Figure 7 1 4 2 3 Spare parts 9 Ersatzteile # Designation Part no. 1 0-ring made of EPDM for sterile design, 23,4 x 3,5 mm 024 365 D 1 0-ring made of EPDM for flange design, 32,5 x 3,6 mm K03 246 2 0-ring made of viton for protective cap, 25 x 1,5 mm 024 336 D 3 Blue connection cable, 2 m with connector 254 634 2 3 Blue connection cable, 5 m with connector 254 634 5 3 Blue connection cable, 10 m with connector 254 634 0 4 Union nut R 11/4" for sterile design 032 126 Pfaudler GmbH 7
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