User`s Manual - Applied Measurement and Control
Contents
1. Size of the O ring EPDM A 17 12X2 62 K1500BR B 20 30 X 2 62 K1500BJ C 25 12X1 78 K1500BS D 17 12X2 62 K1500BR 13 9 ACCESSORIES PH18 differential pH sensor Number K1500BJ K1500BR K1500BS K1500BT K1522ER K1522EQ K1522ET K1522ES K1522MV Description Q Set O rings 20 3 x 5 2 62 EPDM unit Set O rings 17 12 x 2 62 5 EPDM unit Set O rings 25 12 x 1 78 1 EPDM unit Nut 1 SWR Straight i weld in adapter SWA Angled 1 weld in adapter SBS Adapter 1 ISO 7 A R1 JIS 1 SNS Adapter 1 1 NPT BSA1 Blind plug 1 IM 12B6J4 E A 14 APPLICATION DATA SHEET PH18 DIFFERENTIAL PH SENSOR a Please complete a separste form for each process stt eem Customer 10 be analyzed and reum marked fer the attertion of Address Contact Telephone 1 Process data Description Application o Pulp amp Paper O Power O Chemnicas O Phamaceitical O one Oper tion O Batch O Continuous C Meriter O Corra Type of Solution pH Velie Ne LL Min Conductivity V abe Nor Min Temperature PC F No LI Mn Pressure psg bar kg cm Nar cC Min Flow Rate mics A s No LL Mn Concentration d Saks Concertra ion of Organics Types e Teed Probleme with O Fouling O Pasing O Coating Abradon O Other present measuring procedure Clearing Steeit ation O wr roduct DO Sean D Causic C Het Weer O cree Description Othe Valse pH Temperature fO2. User s Model PH18 eb Differential pH sensor x Manual P 9 Lu Made by BPiitillili IM 12B6J4 E A 1st edition Rev 4th edition H TABLE OF CONTENTS PREFACE aee denen erts EO dee rie Po ERE eee das xe TRI Ven ee edi nv Nds 1 LINTRODUCTION iere nene enne x ee PEE e eR ORO eh rx ea un 3 2 GENERAL SPECIFICATIONS sse ene 5 2 1 Model PH18 differential pH sensor nennen enne 5 2 2 Model WU18 cable for PH18 sensor ssssssssseseeseeeee nene 6 2 8 Dimensions of the PELT8SA uertit rrt Yee an peated 7 S THE TYPE 18 PH PROBE cse nenne n ek pl Xa PI nae 8 3 1 Typical applications ia viov tede Dre ro ee YO Pete ava TOt HT RTT vC eod 8 3 2 Handling information for the glass lined pH probe sm 8 3 83 Sterage and hydration uci res eerte erre Fo Ye p er a d ee ERR Fee eed 8 IE Maii EE 8 3 5 PH18 Installation examples eerie teen ee nnn ho rire Reed anne rn 9 4 EXA PH202 OR PH402 INSTRUMENT meme 10 4 1 Set up 5 CALIBRATION rio cone HO GIO YER PERO Ge Her XII He EY YI E rib ges 11 5 T Galibratlon Sett UPa crore een tient catia atari en ALG 11 5 2 ISOPOLEMMalSOFA ValVIGs o Reno tix Febr pora ether rens PARES Ee phos issues aktcaaatveheae 11 S 3 SEOPE ym n11 SAAS LIPPE inkl 5 5 Process Temperature compensation sssssssseeeeeeeemeeennnnn 11 6 CLEANING STERILIZATION memes 12 6 1 Acceptab
3. F Pressure getts Type 18 probe data Seracr Mourting Connedion 25 mn O NPT 4SBSPT Others Wetted Materials 318 Stainkes See Enara Orngr EPDM Karen Immersion Length 150 mm 5 9 Inches Distance between Sen scr and hstroment feet or meters Senso model code PHIG Cable mode cxie WUIT amp Yokogawa Confidential IM 12B6J4 E A 15 IM 12B6J4 E A 16 YOKOGAWA 4 EUROPEAN HEADQUARTERS Yokogawa Europe B V Databankweg 20 3821 AL AMERSFOORT The Netherlands Tel 31 33 4641 611 Fax 31 33 4641 610 E mail info yokogawa nl www yokogawa europe com THE NETHERLANDS Yokogawa Nederland B V Hoofdveste 11 3992 DH HOUTEN Tel 31 30 635 77 77 Fax 431 30 635 77 70 AUSTRIA Yokogawa Austria Ges m b H Franzensbr ckenstrasse 26 A 1021 WIEN Tel 43 1 2165 043 0 Fax 43 1 2165 043 33 BELGIUM Yokogawa Belgium N V S A Minervastraat 16 1930 ZAVENTEM Tel 32 2 719 55 11 Fax 32 2 725 34 99 FRANCE Yokogawa Contr le Bailey S A V lizy Valley 18 20 Rue Grange Dame Rose 78140 VELIZY VILLACOUBLAY Tel 33 1 39 26 10 00 GERMANY Yokogawa Deutschland GmbH Berliner Strasse 101 103 D 40880 RATINGEN Tel 49 2102 4983 0 Fax 49 2102 4983 22 HUNGARY Yokogawa Hungaria Ltd Galamboc u 30 1119 BP Budapest Tel 36 1 204 2797 Fax 36 1 204 2781 ITALY Yokogawa Italia S r l Vicolo D Pantaleoni 4 20161 MILANO Tel 39 02 66 24 11 Fax 39 02 645 57 02 SPAI
4. 12 kV and conditioned for 5 hours in steam at a temperature of 134 C 3 3 Storage and hydration The PH18 Probe can be stored dry for an indefinite period of time at temperatures between 30 and 80 C After prolonged storage or if this is a new probe from the factory a simple steam sterilization should be performed for 15 30 minutes prior to calibration This procedure revitalizes the probes giving it a stable reference potential If steaming is not possible soak the PH 18 for 45 60 minutes in hot water 65 to 85 C If steaming or a hot soak can not be done place the Probe in a standard pH Buffer solution for 24 hours prior to installation The probe must be immersed so that both measuring elements are covered with buffer IM 12B6J4 E A 3 4 Installation Procedure 1 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 4 The cable with high temperature stability blue must be fastened vibration free The cable must not be lai
5. 9 kg 10 m approx 1 4 kg MODEL AND SUFFIX CODE Option Description code Cable for Differential pH Sensor 02 meter connection cable 05 meter connection cable 10 meter connection cable IM 12B6J4 E A 2 3 Dimensions of the PH18 SA in mm inches O Uim 018 0 72 Fig 5 PH18 SA and the adapters Fig 6 External dimensions of the PH18 SA SWR SWA SBS BSA1 NS Fig 7 Options of the PH18 SA IM 12B6J4 E A 3 THE TYPE 18 PH PROBE 3 1 Typical applications e Fermentation e Continuous reactions e Production of diary products e Product monitoring 3 2 Handling information for the glass lined pH probe The differential pH probes are pressure and thermal shock resistant due to the fused steel enamel construction The probes have a very high mechanical stability and are extremely strong 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 enamel may flake Enable the EXA impedance monitoring If sensor damage is indicated the measuring probe must be immediately removed within 24h after an alarm message All probes for use in the food sector are tested with a voltage of
6. in the strictest confidence To maintain traceability tne completed application data sheet will form part of the contract of sale Yokogawa offers no function guarantee for applications where the attached data sheet page 16 has not been satisfactorily completed This does not affect the normal Yokogawa warrantly covering defects in materials or workmanship MODEL AND SUFFIX CODE Description Model PH18 Differential pH sensor Sensor Compatible with 25mm mounting process connection ri D Note p ring Ethylene propylene EPDM The sefisor is supplied with material cable connector For first Instruction Ej sss English language specliod as well Ges parod manual J N No manual Options SA SWA Angled weld in adapter 58316 Note The material certificate 3 1 B is supplied with the sensor and the options SWR Straight weld in adapter SS316 SNS Adapter 1 NPT S8316 SBS Adapter ISO 7 1 R1 JIS 1 SS316 Blind plug SS316 EPDM O ring IM 12B6J4 E A 6 2 2 Model WU18 cable for model PH18 differential pH sensor Max temperature 110 C 230 F Material Thermoplastic Rubber T P R Colour Blue Shipping details sensor and adapter Package wxhxd 350 x 220 x 110 mm Weight approx 1 4 kg Shipping details cable Package wxhxd 350 x 220 x 110 mm Weight 2 m approx 0 6 kg 5 m approx 0
7. 0 1 by using the and gt keys This disables the As Pot check which is not appropriate for the PH18 system Once the jumpers and impedance Service Codes 03 amp 04 Calibration Check 05 and Temperature element have been set correctly wire the probe cable to the instrument as shown in Fig 13 Power wiring instructions are located in the respective instrument manuals PH202 See section 3 4 3 on page 3 6 in the PH202 Instruction Manual IM 12B6C3 E H PH402 See section 3 3 3 on page 3 5 in the PH402 Instruction Manual IM 12B6B3 E H Measuring range PH of sample Fig 13 Connection diagram WU18 for PH402 and PH202 IM 12B6J4 E A Fig 14 Corrosion curve of the Mode PH18 Enamel 5 CALIBRATION 5 1 Calibration set up All pH sensors are characterized by Isopotential ITP Asymmetry Potential ASY and SLOPE SL Typically the ITP is set by the factory for specific sensor types and the ASY and the SL are adjusted by the user during his buffer calibrations Calibration of the PH18 is slightly different from calibration of conventional pH sensors due to the differential nature of the measurement The ITP and SL are set during commissioning and ASY is adjusted by the user during his Grab Sample calibrations 5 2 Isopotential pH value ITP as function of Conductivity for Na CI gc ee LL ETE FETU LUI uM ui 2 NUT THM TERTII TEE s ELE e TUR 0 01 0 1 1 10 100 mS c
8. J4 E A 10 4 EXA PH202 OR PH402 INSTRUMENT 4 1 Set up The EXA PH202 and PH402 are both designed with dual matched high impedance inputs which are necessary when using a pH probe like the Model PH 18 with both a measuring and a reference electrode that are high impedance To prepare the EXA instrument to work with the PH18 make sure the input impedance jumpers are placed in the correct positions PH202 See table 3 1 and fig 3 8 on page 3 7 in the PH202 Instruction Manual IM 12B6C3 E H for jumper positions PH402 See figure 3 9a on page 3 8 in the PH402 Instruction Manual IM 12B6B3 E H for jumper positions Since the Model PH18 has high impedan ces for both the measuring and the reference elements the high impedance check functions Service Codes 03 amp 04 must be set up according to the procedures outlined in Section 5 3 1 in either the PH202 or the PH402 Manual The Calibration check also needs to be changed Here you are instructed to set 1 15 MEASURE i 8 16 SCREEN 2 17 SCREEN 2 13 REFERENCE i 14 LIQUIDEARTH i 486 12 TEMPERATURE 1 3 11 TEMPERATURE 2 Model PH18 sensor Service Code 03 Change settings from 1 1 1 to 1 0 1 by using the and gt keys Low limit 1Megohm High limit 1 Gigaohm Service Code 04 Change settings from 0 0 1 to 1 0 1 by using the and gt keys Low limit 1Megohm High limit 1 Gigaohm Service Code 05 Change settings from 1 1 to
9. N Yokogawa Espa a S A C Francisco Remiro N 2 Edif H 28028 MADRID Tel 34 91 724 20 80 Fax 34 91 355 31 40 IM 12B6J4 E A Copyright Subject to change without notice UNITED KINGDOM Yokogawa United Kingdom Ltd Stuart Road Manor Park RUNCORN Cheshire WA7 1TR Tel 44 1 928 597100 Fax 44 1 928 597101 AUSTRALIA Yokogawa Australia Pty Ltd Private mail bag 24 Centre Court D3 25 27 Paul Street North NORTH RYDE N S W 2113 Tel 61 2 805 0699 Fax 61 2 888 1844 SINGAPORE Yokogawa Engineering Asia Pte Ltd 11 Tampines Street 92 SINGAPORE 528872 Tel 65 783 9537 Fax 65 786 2606 JAPAN Yokogawa Electric Corporation 2 9 32 Nakacho Musashino shi TOKYO 180 Tel 81 422 52 5617 Fax 81 422 52 0622 SOUTH AFRICA Yokogawa South Africa Pty Itd 67 Port Road Robertsham Southdale 2135 JOHANNESBURG Tel 27 11 680 5420 Fax 27 11 680 2922 UNITED STATES OF AMERICA Yokogawa Corporation of America 2 Dart Road NEWNAN GA 30265 1040 Tel 1 770 253 70 00 Fax 1 770 251 28 00 CENTRAL EAST REGION Via Yokogawa Austria Czechia Slovakia Poland Croatia Slovenia Jugoslavia Bulgaria Romania Macedonia Bosnia amp Herzegovina Distributors in Denmark Finland Greece Norway Portugal Russian Federation Sweden Switzerland and Turkey Block 02A 01 99 04 904 A Q Printed in the USA
10. d Handle with care Although the PH18 has a weatherproof construction the connections can be harmed if it becomes submerged in water or becomes excessively wet Do not use an abrasive in cleaning the PH18 Notice Contents of this manual are subject to change without notice Yokogawa is not responsible for damage to the sensor poor performance or losses resulting from such if the problems are caused by 1 Incorrect operation by this user 2 Use of the sensor in the wrong applications 3 Use of the sensor in an adverse environment or incorrect utility program 4 Repair or modification of the sensor by an engineer not authorized by Yokogawa Warranty and service Yokogawa products and parts are guaranteed free from defects in workmanship and material under normal use and service for a period of typically 12 months from the date of shipment from the manufacturer Individual sales organisations can deviate from the typical warranty period and the conditions of sale relating to the original purchase order should be consulted Damage caused by wear and tear inadequate maintenance corrosion or by the effects of chemical processes are excluded from this warranty coverage In the event of warranty claim the defective goods should be sent freight paid to the service department of the relative sales organisation for repair or replacement at Yokogawa discretion The following information must be included in the
11. d together with power cables oN Only suitable transmitters with symmetrical high impedance inputs may be used The following units are approved e Yokogawa EXA PH 202 e Yokogawa EXA PH 402 3 5 PH18 Installation examples Fig 11 The primary adapter is used to make a connection to the process used by the transmitter as the liquid earth Solution ground This is needed for optimum stability of the measurement and is used in the impedance checking circuit Example A Straight weld in adapter through a vessel wall Example B 1 Screw in adapter with existing pipe nipple through a vessel wall Example C Angled weld in adapter in large bore pipe Example D Angled weld in adapter mounted in a bend Example E Screw or weld in adapter mounted in a large bore pipe Example F Screw or weld in adapter mounted on top of a large bore pipe Socket for connection cable Primary adapter pH enamel Reference enamel Fig 12 Model 18 elements Note 1 When measuring in plastic tanks or pipes ensure that the adapter is wetted by the process Avoid installations where an air pocket can be created see fig 12 F This isolates the adapter and hence loses the liquid earth connection Note 2 Flow rate from the side of the sensor Fig 11 should not exceed 2 meters second in low viscosity fluids In high viscosity fluids gt 5cP use only installation as shown in Fig 12 D IM 12B6
12. l pH sensor It does not measure absolute pH except in limited applications It does however measure a single control point accurately repeatably and with minimum maintenance IM 12B6J4 E A Measuring Enamel mV vs PH in solution containing 0 1N Nat m v Operating range 0 2 4 6 10 12 te PH of sample Fig 1 Reference Enamel mV vs PH in solution containing 0 1N Na m v 58858 82828 Operating range 0 2 4 5 10 12 t pH of sample Fig 2 PH18 system output pH reading vs pH in 10 solution containing 0 1N Nat pH a Operating range Cn MYR ATD 1H wD Fig 3 10 20 30 40 Fig 4 IM 12B6J4 E A 2 GENERAL SPECIFICATIONS 2 1 Model PH18 differential pH sensor Temperature sensor Pt1000 Q RTD Wetted parts pH sensor pH sensitive enamel Reference sensor Na sensitive enamel Liquid earth via SS adapter O rings EPDM Adapters S8 316 Max measuring range 8to 11 pH The actual range will be advised with reference to the completed application data sheet Temperature range O to 140 C 284 F Pressure range 1 to 15 Bar 214 psi NOTE The use of this sensor is highly application specific Your local Yokogawa sales office will be pleased to advise on the suitability of your application on receipt of the completed application data sheet Any and all information received by Yokogawa will be treated
13. le CIP cleaning processes sssssseeeemeemeennenn 12 6 2 Sterilization mietliods 5n rtr ener pere dst the RE inne 12 7T MAINTENANDGE ice tea EE AE RM Dear n eee DRY dese 12 8 POSITION OF THE O RINGS sssssssssseeeneenee eene 13 9 AGCESSORIESz sex POPE BR RE SUUM d asda det 13 APPLICATION DATA SHEET PH DIFFERENTIAL PH SENSOR 14 IM 12B6J4 E A A Caution Inappropriate handling can cause damage Striking or scratching the sensor against hard surfaces such as steel stone glass or ceramic may cause damage to the enamel Such damage may not affect the sensor performance immediately but after prolonged exposure to the process flaking of the enamel may occur A Note Enable impedance checks in the PH202 or PH402 The sensor impedance checking can give early warning of damage to the enamel layers If the transmitter signals an impedance failure of the PH18 the sensor should be removed from the process as soon as possible within 24 hours The loss of significant amounts of enamel may thus be avoided IM 12B6J4 E A PREFACE The PH18 should only be used with equipment that meets the relevant IEC American or Canadian standards Yokogawa accepts no responsibility for the misuse of this unit The PH18 is packed carefully with shock absorbing materials nevertheless it may be damaged or broken if subjected to Strong shock such as if the package is droppe
14. letter accompanying the returned goods 1 Part number model code and serial number 2 Original purchase order and date 3 Length of time in service and a description of the process 4 Description of the fault and the circumstances of failure 5 Process environmental conditions that may be related to the installation failure of the device 6 A statement whether warranty or non warranty service is requested 7 Complete shipping and billing instructions for return of material plus the name and phone number of a contact person who can be reached for further information Returned goods that have been in contact with process fluids must be decontamina ted disinfected before shipment Goods should carry a certificate to this effect for the health and safety of our employees Material safety data sheets should be included for all components of the processes to which the equipment has been exposed Unpacking and checking Upon receipt of the goods carefully inspect the shipping package for any evidence of damage If the carton is damaged notify the shipping agent and the sales organisation immediately If the shipping package is not damaged remove the products and parts Confirm that all items shown on the packing list are available and that the package does not contain any parts or accessories fillers Notify the sales organisation if items are missing PH18 sensor The box of the PH18 sensor contains the fol
15. lowing items Sensor complete possible options check part number for possible options instruction manual material certificate and quality inspection certificate The WU18 cable is packed separately IM 12B6J4 E A 1 INTRODUCTION The PH18 is not a conventional electrode It relies on two dissimilar ion sensitive enamel membranes to generate the signal The measuring element is like a pH electrode and the reference like a Sodium ion electrode Therefore the PH18 can only be used in combination with pH meters that feature 1 Dual high impedance inputs 2 Adjustable setting for Isothermal Point 3 Adjustable temperature coefficient The Yokogawa models PH202 and PH402 satisfy these requirements In both cases the membrane enamels are bonded directly to the metal substrate with no filing solution The response curves Fig 1 pH Fig 2 reference and Fig 3 application range show the way in which the potential is generated at each element and combined in the output of the sensor Fig 1 Above pH11 the effect of sodium on the pH membrane starts to cause non linearity Sodium error Below pH3 the high Hydrogen ion content causes a change in the reference response A linear response to pH is obtained between 3 and 11 pH A plot of reference voltage against Sodium content Fig 2 Fig 3 Fig 4 The revolutionary measuring principle has some big advantages The absence of filling solutions and reference ju
16. m pH m a The default setting for the Isopotential point is O mV at 7 00 pH because most manufacturers of Glass electrodes use 7 pH as internal fill solution The PH18 differential sensor has two measuring elements one pH element which has an Isopotential pH value of 1 pH and one pNa element which has an Isopotential pNa value of 2 The Isopotential pH value of the differential sensor depends on the Salt concentration It is recommended to set the ITP as a function of the Conductivity according to the graph 5 3 SLOPE The default setting for SLOPE is 10096 of theoretical value which is 59 16 mV pH 25 C It is only possible to calibrate the SLOPE if pH buffers are used with identical salt concentration These buffers are not commercially available so it is recommended not to perform a SLOPE calibration but leave the analyzer in its default settings It is however recommended to perform a regular SLOPE check to verify 11 proper functioning of the sensor 5 4 ASYMMETRY Potential The default setting for Asymmetry potential is O mV at Isopotential pH value This value is always wrong for the PH18 sensor and therefore the Asymmetry Potential must be calibrated always This cannot be done with conventional pH buffer solutions since these buffer solutions will have salt compositions which differ from the actual process Therefore the calibration is done using the grab sampling method During the most importa
17. ncreased corrosion NOTE With alkali cleaning corrosion 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 50 C 6 1 Acceptable CIP cleaning processes 1 1 5 2 alkaline solution max 85 C max 1 hour 2 1 5 acid HNO3 50 C max 15 min 3 Steam 134 C max 2 hours After cleaning with alkaline solution without acid and steam sterilization a transitional measuring error may occur if the wetting time is too short 6 2 Sterilization methods The probe is resistant to the following sterilization methods e with product e with steam e with alcoholic solutions e with antiseptic solutions IM 12B6J4 E A 7 MAINTENANCE The PH18 does not normally require maintenance as long as it is kept clean Buffer checks may be done if it is suspected that the sensor performance has drifted appreciably It is best however simply to do a single point Manual calibration against a grab sample taken at the process temperature and normal pH value For cleaning or removal of residues dilute acids may be used for a short time at room temperature only Limescale may be removed with commercially available antiliming agents The non abrasive material intended for ceramic cookers may be used to remove Sticky coatings from the PH18 Do not use any metallic or abrasive substances 8 POSITION OF THE O RINGS PH18 SA
18. nctions virtually eliminates the problems caused by aging and pollution of the reference sensor Regular cleaning of the sensor virtually eliminates drift and the sensor benefits from a very long working life It is vital however to fit the sensor to the application correctly The special nature of the reference element dictates that there must be a certain Sodium level in the process Fig 4 shows a plot of reference voltage against Sodium content Because of the exponential nature of the response it is plain that above about 0 5 N Na 30 g NaCl in the solution the reference output remains virtually constant Of course when the Sodium concentration remains constant in a process the reference voltage will also be constant at much lower levels of Sodium It is because of the need to evaluate the chemistry of the process that it is necessary to have an Application Data Sheet page 16 completed before approval for this sensor can be made The mechanical construction of the sensor also means that it may be used in processes involving both high temperatures and pressures By eliminating the filling solutions the sensor is truly robust and can even withstand severe thermal shocks that would ruin most systems The stainless steel mounting adapter forms the liquid earth solution ground connection needed to ensure best stability of measurement EXA also uses this connection in the diagnostic circuit The PH18 is a differentia
19. nt stage of the pH control application a sample is drawn and the pH of the sample is measured with a calibrated conventional pH meter The analyzer is adjusted to this value using the MAN CAL mode Notes This adjustment should be done at the normal working temperature at the most important stage of the process the control setpoint or the critical part of the pH profile This avoids the need for process temperature compensation for constant temperature processes 5 5 Process Temperature Compensation This setting is needed only when the temperature of the process is not reasonably constant When setting process TC it should be done before step 5 4 to avoid influencing the Asymmetry potential calibration The procedure is as follows Allow sensor to stabilize fully in the process Note down the temperature and pH readings t1 amp pH1 Allow sample and sensor to cool together to room temperature and stabilize Again note down the temperature and pH readings t2 amp pH2 T C 9H1 pH2 x10 t1 t2 pH 10 C Note to calculate TC from temperature readings in Farenheit TC pH1 pH2 x18 t1 12 IM 12B6J4 E A 12 6 CLEANING STERILIZATION The probe can be cleaned sterilized inside the reactor For CIP cleaning it must be ensured that the admissible alkali and acid concentration as well as the maximum temperature or cleaning time are not exceeded Otherwise the enamel of the electrode would be subject to i
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