MS2500L Manual - Alabama Specialty Products, Inc.
Contents
1. 30 Assembly DraWiNg EE 31 36 Appendix Parts 37 Appendix Effects of Process Variables 38 Temperate E EE EE EE EA 38 a A EE E 38 Oxygen coca aenteeessectecatenenaeenes 38 38 Suspended Solids 39 El ctrode Potential 41 Common Corrosive A genis EDES 43 App ndix D Warranty 44 Appendix Maintenance and Repair Instructions 45 I Introduction A General Description The MS2500L corrosion rate transmitter is a two wire 4 20mA current loop transmitter for corrosion measurements using the three electrode linear polarization technique LPR Functionally the MS2500L transmitter operates under the same principles as the automatic LPR instruments offered by Metal Samples Corrosion Monitoring Systems with the exception of its low power current loop operation Figure 1 MS2500L The MS2500L transmi2. 12 14 14 B LPR Measurement 15 16 Description 17 Operation Modesa 20 Procedure 21 21 B Eg ipme nt Needed 21 ROWSE 21 21 E Zeroing PN 22 Current Span Adjustment 22 DISCOMMEC TION 22 strument Testing and 23 Recommended Test 23 Board 23 Electrostatic Shield Remy all eee 23 D 24 24 VIL Current Loop and 28 Recomme nd d Test 28 B Instrument and Loop Verification el elie 28 C Probe Element Testing ae ice ees eE ede rE E EEE EEEE REE 28 D Current Loop Isolation Testing sissen oneni enee ea i 29 Appendix
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4. POLLO 5 3 9 1 079 98 30 NOTLYTIVISNI 1100002 NI 1715 31872 9 1 13938 01 13 OF XW Y3LLIWSNYEL Appendix Parts List 1 MS2500L Reference Designators Part No Description Quantity A1 IN2500L 1 Measurement and Control Board A2 IN2500L 2 Loop Control amp Timing Board IN2500L 12 Enclosure Assembly AC1 IN2500L 3 IN2500L 4 Cable Assembly Accessory Kit MN N A Operation Maintenance Manual 37 Appendix Effects of Process Variables 1 Temperature As a general rule increasing temperature increases corrosion rates This is due to combination of factors first the common effect of temperature on the reaction kinetics themselves and second the higher diffusion rate of many corrosive by products at increased temperatures This latter action delivers these by products to the surface more efficiently Occasionally the corrosion rates in a system will decrease with increasing temperatures This can occur because of certain solubility considerations Many gases have lower solubility in open systems at higher temperatures As temperatures increase the resulting decrease in solubility of the gas causes corrosion rates to go down 2 pH Corrosion rates almost always increase with decreasing pH incr
5. gt 2 2e E 0 00 volts Some other generalizations drawn from the standard oxidation reduction potential table are 1 Oxygen is a stronger oxidizing agent than hydrogen ion 2 Iron is more reactive than lead copper or silver 3 Gold is very unreactive More Reactive Reaction Eo volts Na Nat e 2 71 Mg 2e 2 38 Al Altt 1 66 Zn Zntt 0 763 Fe 2 0 409 Ni 2 0 250 Pb Pbt 2 0 126 2 2 0 00 Reference 2 0 34 2 4 0 401 2 0 771 0 799 2H 2 0 905 2 1 06 2 4 4e7 1 23 2 Cl 2e 1 36 Pt Pttt 2 1 2 Au 1 498 More Noble 42 Galvanic Series The table below is a simple version of the galvanic series of alloys in seawater Because electrode oxidation reduction potentials only apply to pure elements and true compounds another system was developed to compare the relative reactivity of alloys in an environment This series has the added advantage of allowing you to predict the galvanic behavior of certain alloy pairs in an environment If a pair of alloys listed in the series are coupled the alloy higher in the list will be corroded more rapidly than if it were uncoupled and the alloy lower in the series will be protected or corrod
6. Caution When instrument is operated in hazardous areas all power to the instrument must be removed before opening cover The instrument was designed for easy board access and replacement in the field However it is recommended that all electrical tests be performed in laboratory or bench top environ ment B Board Removal After unscrewing enclosure cover and removing probe and loop current connectors remove intercon nected boards from bracket The boards should easily slide out from bracket C Electrostatic Shield Removal Using a 1 16 Allen wrench remove the knobs from the shafts by loosening the 4 Allen head set screws Then remove the two switch mounting nuts using a 3 8 socket wrench Remove the two Phillips head screws from the top of the electrostatic shield and remove the electrostatic shield 23 D Visual Inspection Carefully separate the boards and inspect the two circuit boards for Signs of overheating or overheated components e Short circuits caused by foreign debris Broken or cracked solder traces e Corrosion on connector surfaces e General corrosion attack to boards or components in general Signs of moisture damage or condensation e Tampering or abuse Inspect all cable connections and connectors for integrity Ifnecessary use DVM set to read ohms continuity to test cables and connectors E Electrical Testing Carefully reassemble the two circuit cards For testing or calibration
7. 14 76cm x 11 43cm x 12 22cm Explosion Proof FM CSA CENELEC UL Class I Groups B C D Class II Groups E F G Class NEMA 4X 7BCD 9EFG 0 728 H x 1 756 W 1 85cm x 4 46cm Bolt Pattern with 1 4 20 Tapped Mounting Holes or Be Mounted on a 1 2 to 2 1 27cm to 5 08cm Pipe Using Supplied Hardware 32 to 158 F 0 to 70 C 32 to 158 F 0 to 70 C 3 Electrode LPR Potential 3 Electrode 0 100 Potential 1V 0 1 to 99 9 minutes 111035 VDC 10 3 05 m 4 20mA Current Loop Output e Switch selectable measurement type and cycle time e Loop powered Accessory Items 10 Probe Cable attached Meter Prover Mounting Hardware Operation Manual Summary The MS2500L transmitter moves on line corrosion monitoring into realm of conventional plant practice by placing the D C powered transmitter close to the corrosion rate probe the sensor and using the two wire signal loop to provide both the power to the transmitter and the proportional signal corresponding to the data User Selectable Operation Switches on the transmitter s circuit board allow the user to select necessary parameters such as Operation Mode Track or Sample Cycle Time 1 99 9 minutes Transmitter Data Type Corrosion Rate MPY or Electrode Potential mV Low Cost Since the transmitter is of the two wire type the installed cost of an installation is far less than if the analyzer is located in the contro
8. Connect the negative lead to positive terminal of power supply Attach spare lead to negative terminal of power supply and other end to negative terminal of J3 J6 Note While making connections power supply should be off The power supply DVM and leads will remain in place during all calibrations Turn power supply adjustment all the way down Turn on power supply and DVM Set volt meter to read in the 200 milliamp range 200 0 mA While watching DVM slowly adjust power supply up to 18 Volts making sure that the DVM reading does not exceed 40 0 mA D Frequency Calibration Connect frequency counter ground to pin 8 on U12 and probe to pin 11 on U12 Adjust R50 until the frequency read is 2730 Hz 1 Hz Disconnect frequency counter 21 Zeroing Adjustments Connect shorting plug to Set switch SW1 to the Offset position and SW to the Track position Using the second DVM connect the positive lead to pin 6 on AR2 and the negative lead to wire on shorting plug Adjust R12 until a reading of 0 0 mV 0 1 mV is shown on second DVM Move same two leads to pins 2 and 3 AR7 and adjust R46 until it reads 0 0 mV 0 1 mV While looking at other original meter adjust R25 until the current reads 4 00 mA F Current Span Adjustment Replace shorting plug with the instruments meter cable Insure that 10 MPY prover is still in place Hook the positive lead on second DVM to the A red position on J1 J5 and the ne
9. purposes the instrument can be operated without the electrostatic shield However it is necessary to replace the two screws used to secure the upper part of the shield These two points are used for board interconnection of the instru ment ground It will also be necessary to temporarily replace the two control knobs by tightening only the two set screws used to bind the flat parts of the switch posts Connect the spare cable assembly to the connector on the Al Board Note that the cable shield need not be connected for testing purposes Place a 10 MPY prover on the cable connector With the power supply turned off connect the power supply and the current reading DVM to the A2 Board connector observing proper polarity Set the mode of operation to LPR and the output mode to SAMPLE Refer to the labeling on the electrostatic shield Set the SAMPLE TIME to 00 1 minutes Turn on the power supply and observe the current If the unit functions properly the current reading should settle out to 5 6mA 0 1mA after 2 to 3 polarization cycles If the unit malfunctions one or more of the following symptoms will appear 24 1 The unit gives incorrect readings Error gt 40 1 mA 2 The unit is erratic or has intermittent operation Readings fluctuate 3 The unit draws excessive current 30mA or more Isolate the problem to the faulty board by substituting a spare working board and retesting the instru ment following the above procedures At thi
10. the probe location If this turns out to be in conflict with the ideal considerations the probe should be installed keeping in mind the problems that may arise PAIR Probe Assembly All probes with replaceable electrodes are shipped with the electrodes and gaskets in a separate packet if the electrodes are purchased with the probes When ready to install open the packet and place one of the gaskets on each of the three mounting pins Pin A is connected to the Reference electrode Pins B and D are connected to the Test electrode and Pin C is connected to the Auxiliary electrode PATAN P D 4 Figure 5 Electrode Mounting Configurations 12 The electrodes should not be handled with bare sweaty or oily hands If possible pick up the electrodes with a paper towel or clean cloth and thread onto each of the three mounting pins The electrodes should be firmly hand tightened in place sufficiently to deform the gasket A one inch piece of plastic tubing slipped over an electrode is an effective means of tightening it on the probe without soil or damage Do not force with pliers or in a vise as this will mark the surfaces Do not use thread lubricant The mild steel electrodes have been given a surface preparation to permit fastest possible equilibrium to the system Any foreign material such as grease oil or sweat will delay obtaining uniform readings Should a change in loca
11. 0 EL 671 EL 672 EL 673 EL 687 EL 681 Reference Electrode with one VITON Gasket Aluminum Alloy 6061 standard Copper 99 0 Pure Brass 85 15 Admiralty Metal Copper Nickel Aluminum Bronze 92 Cu 8 Al Copper Nickel 70 30 Cold Rolled Mild Steel 1018 0 250 Dia Cold Rolled Mild Steel 1018 0 375 Dia 304 Stainless Steel 316 Stainless Steel 410 Stainless Steel 430 Stainless Steel 304 Low Carbon Stainless Steel 316 Low Carbon Stainless Steel Hastelloy Hastelloy C Hatelloy N Nickel 200 600 Inconel 625 Incolloy 800 Incolloy 825 Monel Alloy 20 Zinc Titanium Tantalum Zirconium Aluminum Brass Replaceable Electrode Assembly for PR 556 E Flush Mounted Probe Registered trademark of Beckman Instruments Inc 2 Registered trademark of DuPont 3 Registered trademark of Stellite Division Cabot Corp Registered trademark of Huntington Alloys Inc 5 Registered trademark of Carpenter Technology 10 Probe Placement Proper probe location is the first and one of the most important considerations in obtaining pertinent data with the corrosion rate instrument Any system can be expected to have corrosion occurring at several rates as a function of location within the system The different rates may be due to changes of temperature changes in velocity impingement effects differences of metallurgy variations in character of fluid stream etc It is
12. MPY value 5 5 MPY The polarization current is relaxed for the same duration after which the process can then be repeated The MS2500L instrument incorporates the circuitry necessary to perform the above steps as well as the ability to monitor and transmit the potential difference between the reference and test electrodes Following the above description the circuitry is divided into several sections Potential measurement and recording Polarization reference and current control Clock and timing circuits Polarization current measurement and conversion General circuitry required for the operation of the instrument Power supplies e Current loop sensing and control Power on reset 15 Basic Structure The circuitry for the MS2500L is contained on two circuit cards The Board contains circuitry for Corrosion potential measurement Corrosion potential null and hold 10 millivolt probe polarization and reference Polarization current control measurement and conversion The A2 Board contains circuitry for Power supplies Clock and timing control circuits Power on reset Current loop sensing and control Output sample and hold 16 Circuit Description The following circuit description describes the behavior of the circuitry in the LPR mode with the output mode set to SAMPLE This is the most common mode of operation for this type of instrument Differ enc
13. Metal Samples Corrosion Monitoring Systems D MS2500L Transmitter Operator s Manual Metal Samples Corrosion Monitoring Systems A Division of Alabama Specialty Products Inc 152 Metal Samples Rd Munford AL 36268 Phone 256 358 4202 Fax 256 358 4515 E mail msc alspi com Internet www metalsamples com Houston Office 6327 Teal Mist Lane Fulshear TX 77441 Phone 832 451 6825 Table of Contents T Introduction Seen ae ss dc 1 General Description 1 B 2 3 4 SMTA 5 ss TriState 6 MS2500L Transmitter 6 MS2510 Receiver Installation 6 7 A Cycle Vite 7 as haw Sree vee I se eee amp MS2510 Receiver Power Supply amp Probes ANd Electrodes a 9 Electrodes Normally Carried in 10 D Probe placement 11 Probe Installation 11 F PAIR Probe Assembly
14. Purchaser s expense to and from Metal Samples Corrosion Monitoring Systems which shall have the right to final determination as to the existence and cause of a defect The foregoing shall constitute the sole and exclusive remedy of any purchaser of Metal Samples Corro sion Monitoring Systems products for breach of warranty and IS EXCLUSIVE AND IN LIEU OF ALL OTHER WARRANTIES EXPRESSED IMPLIED OR STATUTORY INCLUDING THE IMPLIED WARRANTIES OR MERCHANTABILITY AND FITNESS IN NO EVENT SHALL METAL SAMPLES CORROSION MONITORING SYSTEMS BE LIABLE FOR SPECIAL OR CONSEQUENTIAL DAMAGES OR FOR ANY DELAY IN THE PERFORMANCE OF THIS WARRANTY DUE TO CAUSES BEYOND ITS CONTROL Orders or request for additional information should be addressed to Metal Samples Corrosion Monitoring Systems P O Box 8 Munford AL 36268 Telephone 256 358 4202 Fax 256 358 4515 The technical information and suggestions contained herein are believed to be reliable but they are not to be construed as warranties since conditions of use are beyond our control Shipping Address Metal Samples Corrosion Monitoring Systems 152 Metal Samples Road Munford AL 36268 Telephone 256 358 4202 Fax 256 358 4515 44 Appendix Maintenance and Repair Instructions This form may be photocopied for use when returning instruments to Metal Samples Corrosion Monitoring Systems for repair Please fill in all known information Enclose copy of the filled in form wi
15. across R23 4 At full scale output the sample and hold develops a 5 0 volt signal thus requiring 20mA loop current to balance the circuit E Operation Modes Offset Mode A mentioned earlier the polarization current and the potential null circuitry are disabled when operating in OFFSET OFFSET modes The reference to the instrumentation amplifier SW1 C is set to the common reference and the output of the instrumentation reflects the cell potential difference This value is sent directly to the output sample and hold circuitry in the OFFSET mode If OFFSET mode is selected AR1 C inverts the polarity and amplifies the signal before it reaches the output sample and hold circuit Track Mode When the TRACK mode is selected the output sample and hold circuitry is set to run repetitive conver sion cycles constantly updating its output on 2 5 second intervals 20 VI Calibration Procedure A Disassembly After unscrewing enclosure cover and disconnecting 15 connector remove interconnected boards 1 and A2 from bracket Remove shield by removing nuts and washers from switches SW1 SW2 and screws Z5 and Z6 Replace both screws B Equipment Needed e 1 Adjustable 18 Volt Power Supply e 2 Digital Volt Meters and Leads 1 Frequency Counter and Probe 1 Shorting Plug 1 Spare Lead C Applying Power Connect positive lead of digital volt meter DVM to the positive terminal of J3 J6
16. ation cycle a conversion is initiated to sample the current amplifier output in the LPR and SAMPLE modes During this conversion process a conversion in process signal is generated by the successive approximation registers This signal is used to disable U15 A thus maintaining a short term sample and hold using C13 and AR7 Once completed the end of conversion signal reenables U15 A and triggers the relaxation portion of the LPR cycle The gain of AR7 rescales the signal to 1 0 to 5 0 volt signal with reference to true ground which is used by the current loop control circuitry 19 Current Loop Control The circuitry for the current loop control is contained on the A2 Board and consists of The current loop sense and balancing amplifier 5 e The current loop control transistor Q1 The current loop sense network R23 R24 R25 and R41 The output of the current loop must be maintained at the desired signal level regardless of the amount of current drawn in order to power the circuitry This is accomplished by using the R23 resistor placed in the loop to develop a voltage drop from 1 0 to 5 0 volts for a current span of 4 20 mil liamps At an output of zero the sample and hold circuitry is at 1 0 volt with reference to ground this voltage is subtracted from the negative voltage developed by R23 using the R24 R41 and R25 network AR5 B senses this difference and biases Q1 until the current loop develops 1 0 volt drop
17. ch the output of the 12 bit D A converter circuit U7 AR4 C and AR4 B using the comparison generated by AR4 D between common and the output of the instrumentation amplifier AR1 A AR1 B and AR2 unto the output of the instru mentation amp is zero This is by setting a bias on the reference of the instrumentation amp SW1 C using the output of the D A converter circuit This scheme nulls the instrumentation output to zero so an offset shift of 10 millivolts can be easily read by the next process step Upon the completion of this process an end of conversion signal is generated by the successive approximation registers This signal is used to trigger the remaining portion of the polarization cycle Ifthe OFFSET or OFFSET function is selected the above scheme is bypassed with the reference point of the instrumentation amplifier SW 1 set to common and the output of the instrumentation amplifier which reflects the potential difference is sent directly to the output circuits or if OFFSET is selected the output is inverted and amplified by 1 18 Polarization Current Control and Measurement The circuitry for the polarization current control and measurement resides on the 1 Board and consists of A 10 millivolt polarization reference made up from the reference portion of AR3 Current drive and scaling amplifier using the power amp portion of AR3 Polarization balancing amplifier AR1 D Current sensing different
18. d BCD value using SW3 SW4 and SWS The timers are cascaded in order to count down upon every pulse generated from the Q14 output of U12 Upon each completion of 17 count down a pulse is generated to reload counters and to initiate either a polarization cycle relaxation cycle initially a polarization cycle depending upon the previous state Pulses from Q14 output of U12 are generated upon 1 10 minute intervals 0 166 Hz which are divided down from the 2730 Hz signal developed by the U16 clock oscillator A 5 332 Hz signal generated by the Q9 output of U12 is also used to clock the sample and hold circuits Potential Sample and Hold Circuits The potential sample and hold and measurement circuits are contained on the 1 Board and are made up of e Aninfinite term digital sample and hold consisting of A bipolar successive approximation ADC using U7 U4 05 and AR4 B C D A 200 millivolt ADC reference using part of AR3 e A low power instrumentation amplifier made up from AR1 A B AR2 R5 R8 and e An inverting amplifier using AR1 C R2 As explained earlier the first part of the LPR measurement process is the sampling and storing of the potential value This is accomplished by a digital sample and hold technique with an indefinite holding capability On the initiation of a polarization cycle a pulse triggers the start ofa successive approxima tion conversion performed by U4 and 05 U4 and 05 swit
19. der Probes and Electrodes The PAIR probes used in conjunction with Metal Samples Corrosion Monitoring Systems corrosion rate instruments are an essential component of a corrosion rate measuring system For this reason the composition of the electrodes installed on the probe must be matched as nearly as possible to the composition of the components of the processing system in which the probe and electrodes are in stalled In addition the placement of the probe is extremely important in obtaining accurate corrosion rate readings Basically a probe is simply a means of mounting the three electrodes which are necessary to make the corrosion rate measurement and provides a means of electrically connecting the electrodes the composition of which is determined by the customer The probes are generally classified into two types laboratory probes and industrial probes All probes are supplied with MIL environmental electrical connectors unless otherwise specified For further information on probes and electrodes contact Metal Samples Corrosion Monitoring Systems P O Box 8 Munford AL 36268 Phone 256 358 4202 Fax 256 358 4515 E mail msc alspi com Internet www metalsamples com Electrodes Normally Carried in Stock EL 600 EL 601 EL 610 EL 611 EL 612 EL 613 EL 614 EL 615 EL 620 EL 621 EL 630 EL 631 EL 632 EL 633 EL 634 EL 635 EL 640 EL 641 EL 643 EL 651 EL 652 EL 653 EL 654 EL 655 EL 657 EL 658 EL 66
20. djust switches to this time interval 6 Set the operation switches to LPR and SAMPLE 7 Cycle the loop power on and off Break Loop 8 The instrument is now in the run mode and will update the current loop output once every two sample time intervals Accessories 52510 Receiver Power Supply When operated together MS2510 receiver and MS2500L transmitter provide corrosion investigator with a low cost 4 20mA corrosion monitoring system Data received from the transmitter is displayed on the receiver s front panel a three digit L E D The three position function switch located at the center of the receiver s front panel permits the data to be displayed in one of two formats depending on switch position milliamps and corrosion rate Located at the back of the receiver are 4 20mA and 10V output terminals for connection of the receiver to a customer supplied computer data logger or recorder connection terminals for the MS2500L and an AC power cord connector General Specifications 52510 Display 3 digit L E D display to give a Loop Current inmA b Probe Reading 0 100 MPY Dimensions Length 5 25 Width 2 0 Height 6 6 Required Installation Space 4 3 x2 Weight 3 Ibs Electrical Specifications MS2510 Power Requirements 120 240V AC 50 60 Hz gt Amp Outputs 24V DC 4 to 20 mA current loop drive 4 20mA isolated output to CPU etc 0 10V isolated output to chart recor
21. e more slowly than if it were uncoupled The table shows why alloys of aluminum and magnesium are galvanically coupled to steel to protect the steel Coupling steel to copper brass or stainless steel accelerates the corrosion of steel Active Anodic Magnesium Zinc Aluminum Tron Steel Lead Brass Admiralty Copper 70 30 Copper Nickel Stainless Steel passive Noble Cathodic 7 Common Corrosive Agents Most but not all of the common corrosive agents encountered in industrial waters are gases The reactions of importance are 2Ht 2e 2H gt H O 4 4 gt 2H 0 O 29 0 4e 40H HCO Cl 2 2 Other corrosive agents occur in industrial waters although infrequently Among these are ferric ion sulfide ion 72 bromine Br and cupric ion Cu 43 Appendix D Warranty Information Metal Samples Corrosion Monitoring Systems warrants that any part of the MS2500L and accessories which proves to be defective in material or workmanship within one year of the date of original shipment to Purchaser will be repaired or replaced at Metal Samples Corrosion Monitoring Systems option free of charge This warranty does not cover 1 probe assemblies 2 items expendable in nature or 3 items subject to damage from normal wear misuse or abuse or failure to follow use and care instructions All damaged items are to be shipped at
22. e three positions on the front panel of the MS2510 are used with the MS2500L One is the loop current in milliamps and the other far right is corrosion rate in mils per year Back Panel The back panel s 10 position rotary switches must be set to 999 when operated in the Corrosion Rate Mode In Current Loop Mode the switch positions do not matter Wire Connections Once the MS2500L is installed connections are made by connecting the red wire coming out of the MS2500L to side of terminals back of the MS2510 receiver labeled LOOP Connect the black wire to the side under LOOP Operation A Cycle Time Predetermination The following procedure assumes both the mechanical and electrical installation of the instrument This procedure also requires that some form of device is available for monitoring the loop ie DVM chart recorder etc 1 Connect the instrument cable to the probe 2 Set the sample time adjust switches on the MS2500L to 999 3 Set the operation switches to LPR and TRACK mode 4 Power up the loop and observe the loop current using a ammeter recorder etc The current reading will change every two seconds These readings will then begin to settle Depending upon the conditions this may take from 30 seconds to 30 minutes Record this time interval 3 _ 8 Time to Settle 4 0 Tine Figure 4 Settle Time 5 Set the sample time a
23. easing acidity This is a direct result of increasing the concentration of an aggressive ion H and increasing the solubility of most potentially corrosive products 3 Oxygen Concentration Oxygen s role in corrosion is as an aggressive gas or oxidizing agent As its con centration increases corrosion rates increase until the rates of diffusion to the sur faces reach a maximum The same principles apply to most other oxidizing agents such as 2 H 2 4 Fluid Velocity The dependence of corrosion rate on fluid velocity is complex In general the higher the velocity the higher the corrosion rate At very low velocities even zero there are diffusion effects that can cause corrosion As fluid velocities increase from stagnant to moderate values the corrosion rates increase Then as the limit of diffusion at a particular temperature is reached further increases in velocity have little effect on the corrosion rate At some point however the velocity reaches such high values that the surface film of the metal begins to be damaged At these veloci ties the corrosion rates resume increasing with the higher velocities 38 5 Suspended Solids An increase in suspended solids levels will accelerate corrosion rates These solids include any inorganic or organic contaminants present in the water Examples of these contaminants include clay sand silt or biomass Some specific contaminants can interfere with the Linear Polari
24. erence to ground Also check COM and COM1 these common reference points should be at 1 volt with reference to ground If left operating for 30 minutes or more the faulty component may overheat If this occurs the component can then be easily located and replaced If not then the component must be located by substitution or the board replaced If the cause of the problem cannot be resolved send unit back to Metal Samples Corrosion Monitoring Systems for repair Use form in the Appendix E of this manual 26 Recalibration Once the instrument has been repaired it should be recalibrated as described by the Calibration Proce dure in Section VI Replacement After repairing or replacing boards interconnect the two boards making sure that the connectors on each board probe and loop current are at the same end and that no pins are bent while inserting Replace the shield after removing nuts and washers from switches Put screws back into boards and nuts and washers back on switches to secure Replace knobs on the switches Reinsert boards back into brackets with connectors facing out Insure that the connectors face their respective access holes in the housing Test the instrument using a prover to insure proper operation 27 Current Loop Operation and Testing A Recommended Test Equipment 1 Portable DVM with the ability to read current 1 10 MPY meter prover 1 1K ohm 1 4 watt resistor B Instrument and Loo
25. es in operation modes are described in following sections Power Supplies The power supply circuitry is contained on the A2 Board This includes A 2 5 volt reference circuit made up of U9 CR6 e The main 6 volt source maintained by AR5 A and 02 The volt common reference maintained by AR6 e The Auxiliary common reference and supply consisting of AR5 A and ARS D The constant current IC U9 and the micropower reference diode CR6 maintain a stable 2 5 volt reference This reference is amplified and regulated at 6 volts by 5 Since this is the main power source for the circuitry the 232222 transistor Q2 in the feedback loop of AR5 A adds extra current drive AR6 contains a built in 200 millivolt reference and a power OP amp Together these are used to supply volt common source for most of the analog and digital circuitry AR5 C and ARS D are unity gain buffers used to supply the power to the clock circuitry which tend to degrade the power supplies Clock Timer and Power On Reset Circuit The clock timing and power on reset circuitry are contained on the A2 Board These circuits consist of e A power on reset pulse generator U17 clock oscillator and divider circuit consisting of U16 012 user programmable timer circuit made up of U8 U10 and U11 SW3 SW4 SWS Upon power up a pulse is generated by U17 which sets the initial states of the timer circuits to the user selecte
26. gative to the B blue position on J1 J5 Set meter to read in the 20 mV range Set SW1 to the LPR position SW2 to the Sample SW3 to 0 SW4 to 0 and SWS to 4 Turn off power supply wait one second and turn it back on Let instrument sit for one full minute Note During this time the second DVM will cycle from 0 mV to 10 mV every 24 seconds During the time that the DVM reads 10 mV adjust until the meter reads 10 00 mV 01mV exactly You have 24 seconds to do this before next cycle Once is adjusted observe meter for two more cycles to insure that 10 00 mV 01mV is held Remove leads from J1 J5 Adjust R45 until original meter reads 5 60 mA G Disconnection Remove power from power supply and remove all leads Replace connectors and instrument shield Put instrument back in the condition that it was first received 22 Instrument Testing and Repair A Recommended Test Equipment 1 Adjustable Power Supply e Digital Voltmeter e Digital Voltmeter with capability of reading current 1 Dual channel oscilloscope 1 10 meter prover 1 Set of working replacement boards 1 Replacement cable and connector assembly Note Unless suitable environment and expertise is available for the testing and repair of sensitive electronics it is recommended that component level testing and replacement for this instrument be performed only by Metal Samples Corrosion Monitoring Systems
27. ial amplifier AR4 A Solid state current control switching U1 A and U1 B Upon the end of conversion signal generated by the potential sample and hold the current control is enabled via SW1 A U1 B and U1 A are enabled allowing a current path through the cell between the auxiliary and test electrodes As current is allowed to flow the potential of the cell voltage between the reference and test electrodes changes AR1 D monitors this change compares it with the 10 millivolt reference generated by AR3 R3 R7and R10 and controls the current drive by AR3 until a balance point is reached where the potential of the cell has changed by 10 millivolts The 1 82K resistor R11 in the feedback loop of AR3 gives a 0 0 1 0 volt drop for a span of 100 MPY using the conversion factor of 5 5 AR4 A is used as a differential amplifier which converts the 0 1 volt drop across toa 0 0 1 0 volt signal which is sent to the output circuitry Output Sample and Hold The output sample and hold circuits are contained on the A2 Board and consist of e An infinite term digital sample hold consisting of a successive approximation ADC using U13 U14 U18 AR9 and AR8 e A short term sample and hold using U15 A AR7 and C13 When operating in the SAMPLE mode there is a possibility of 3 5 hour holds between reading up dates This long hold time is accomplished by a second infinite term digital sample and hold At the end ofa polariz
28. l room and signal cables are run from the sensor to the analyzer Safe The transmitter itself is housed in a compact explosion proof housing Standardized Output Since the 4 20mA data signal from the transmitter is the most common in industrial use today the display of the corrosion rate data is simplified The data may be displayed on a suitable recorder digital voltmeter or on the optional MS2510 digital display unit which will display loop current corrosion rate MPY or electrode potential mV The MS2510 also has an auxiliary power supply for powering the transmitter and a current loop output for passing the data on to another reading device PAIR probes 3 electrode Linear Polarization type can be used as sensors for the MS2500L without modification II Installation Procedures A MS2500L Transmitter Mounting When mounting the MS2500L choose a location that is free from vibration The mounting bracket U bolts can accept a pipe that is no larger than 2 5 inches Always remove power to the instrument when mounting especially when mounting it in a hazardous area See Drawing No 8102 in Appendix A for preferred hardware mounting scheme B MS2510 Receiver Installation The MS2500L transmitter can be used in conjunction with the MS25 10 receiver See Drawing No 8101 in Appendix A for connecting these two instruments together See Section IV for description and specifications of the MS2510 Front Panel Two of th
29. o sion attack or moisture on the boards then the switch contacts are most likely damaged It will be necessary to replace the switches or the boards Check the operation of the power on reset circuit cycle the power off and on and check the output of 17 pin 3 There should be a high pulse for one second after the power is applied to the circuit Check the operation of the system clock U16 pin 3 should show 2750 Hz square wave This 15 divided down to 1666 Hz square wave by U12 pin 3 Check the timer circuits U8 U10 and U11 There should be a pulse each the time the counter reaches 0 at U8 pin 12 and the counters reloaded with the BCD value of the switch settings Check the control circuits U2 B outputs pin 13 and 12 will alternate between polarization mode and relaxation mode upon each countdown of the timer circuits U3 A controls the current gate pin 1 U2 A controls the OCP sample trigger pin 1 and U3 B controls the output sample and hold pin 13 Excessive Current This symptom current gt 30mA is usually caused by a faulty or damaged component which draws excessive amount of supply power Test for a voltage drop across R4 Ifa voltage drop appears current is drawn by the loop control circuit Test the operation of Q1 and ARS Test to see that R23 is not damaged Ifno voltage drop appears current is drawn by a faulty or damaged component Check the V and V rails They should be about 6 volts with ref
30. ollowing basis 1 Locate the probe as close as possible to the warmest section of the system If vaporization 15 experienced in the process the probe should be installed immediately after condensation 2 Ifthe fluid is normally flowing it is recommended that the probe be inserted in such a way as to experience approximate pipe wall velocity The probe should not be installed in a stagnant section of line Some turbulence at an elbow or tee may result in slightly high but acceptable corrosion rate readings 11 3 Direct fluid impingement on probe s electrodes at a very high velocity of about 10 feet per second or so should be avoided as this usually results in abnormally high corrosion rates aggra vated by erosion 4 The probe should be installed in a position where solids are likely to collect Solids can build up on the probe base and electrically short out the electrodes 5 Any surface area in contact with a hydrocarbon phase or gas phase will not be corroding There fore representative maximum corrosion rates are obtained when the total Test electrode surface is in water or electrolyte 6 A bypass loop around a section of the main piping may be considered Probe inspection and electrode replacement can be made without system shutdown Effects of velocity can be checked by throttling of bypass valves The above is furnished as a general guideline The existing physical facilities of most systems will dictate
31. p Verification With the instrument installed and the wiring for the current loop complete install the DVM in the current loop and set it to read current in milliamps Install the 10 MPY meter prover on the probe cable Set the operation switches to LPR and SAMPLE Set the sample time switches to 00 1 minutes The use of the 10 MPY prover insures that there are no ground fault currents caused by a non isolated loop during this step of the test procedure Power up the loop and observe the current After 30 seconds the current should settle out to 5 6 milliamps If the readings are correct the operation of the instrument and the current loop are correct If the readings are incorrect test the voltage at the current loop terminals for the minimum specification of 11 volts Ifthe voltage meets the specification then it is possible that the instrument needs repair or recalibration C Probe Element Testing Set the DVM to read DC voltage in millivolts Test the Offset Corrosion Potential across the Reference and Test electrodes pins A and B on the probe connector For the MS2500L to operate correctly in the LPR mode this offset potential can be no greater than 200 millivolts and no less than 200 millivolts If the OCP does not fall within these limits of 200 millivolts it is possible that a Lazaran type electrode is used for the reference or the reference and test electrodes are of dissimilar metals De pending upon the application this ma
32. ro AMONI puent I t 981412349 permumuo MANUFACTURING DATE 5 122 THY GN 1 a ety A E 28 gt D 4 5 ao 39 gt 4 ZMS 2 22 9 SNOISIARY SENT LL ONY animava BAN PROVO SRAVOTONT 900 2 avarama ONT awos oo 0814109 BBINGENLO MANUFACTURING DATE 123 BIGNAN TV IBN 1 30105 330598 ONTEAL 718 355 916 6 Nid 01 SLOSNNOD 3015 111508 ONY P Nid SEY 01 4934405 813 ONY 9189 SIBI AIGNISSY MNS pl SHY 04 51334903 3015 3 111508 ONY 3015 9 FHL 01 513360 029 ONY 2183 ATEN3SSY 87S FHL 4 9 98 01 5193940 3015 34111508 ONY 30 3015 ONNOYD 01 S1IZNNOI 619 ONY 182 709265 915 FH Qt OL 5123 LINN 30 3015 34111504 ONY 9 Nid Stf 01 519980 412 ONV 0169 BHD ATGN3SSY 8NS FHL imj
33. s point repairs could be considered complete by using the replacement board The instrument can now be reassembled recalibrated and placed back into ser vice However if component level repairs are intended the following guidelines are intended to help isolate the cause of the problem Incorrect Readings Ifthe errors are minimal 2mA this can usually be corrected by recalibration of the instrument Follow the recalibration procedures and retest the instrument If the instrument cannot be recalibrated then check the following points During a relaxation cycle the output of the instrumentation amplifier AR2 pin 6 should be equal to the common reference point If there is an error the problem 15 in the instrumentation amplifier 1 and A2 or the operation of the OCP sample and hold circuit U7 U4 05 AR4 C AR4 B and AR4 D Be sure to check the sample and hold clock U12 pin 13 and the triggering signal U2 pin 1 for this circuit Test voltage between J1 B and J1 A for the 10 00 mV offset during a polarization cycle If there is no offset then check the 200mV reference at AR3 pin and the divider output at AR1 12 10 mV Check the current gate U1 A and U1 B and the current enable pulse at U1 pin 6 Also test CR1 and CR2 If there is an error in the offset gt 1mV during the polarization cycle the output of the instrumentation amplifier AR2 pin 6 should be 10 mV the inputs of AR1 D pins 12 and 13 sho
34. strumentation 2 The4milliamp live zero not only provides current to power the instrument but also provides a method to determine loop failure Ifthe zero output point of the instrument was at zero milliamps there would be no way to differentiate between a zero output or a failure in the loop 3 The transmission of alow impedance signal such as a current rather than a high impedance signal such as a voltage sets up a transmission technique that is much more impervious Generally noises induced onto signal cables are of very high impedances It would take a very large external force to induce a noise signal onto the loop at a current of 4mA or more Again ifa true zero point were used it might be possible to induce a noise error around the zero current level However the use of the 4mA live zero precludes this possibility 14 LPR Measurement Technique The LPR technique is a near instantaneous method for determination of corrosion rates using PAIR probes or similar probes It is a simple process which incorporates several steps 1 2 The potential difference between test and reference electrode is sampled and recorded A current is forced between the auxiliary and test electrodes until the original potential difference is changed by 10 millivolts This polarization current is allowed to settle for a user specified duration The current is then sampled a conversion factor is used to calculate the
35. t then allows this current to settle for a predetermined length of time polarization cycle after which it samples this current and updates the current loop output using the conversion factor of 5 5 uA per MPY Note The surface area of the electrode has been adjusted where 5 5 uA converts to 1 MPY The polarizing current is then turned off and the cell is allowed to relax for the same length of time as the polarization cycle Cycle Time Adjustment The MS2500L uses a digital timing circuit which can be adjusted using three 10 position rotary switches Figure 2 The first switch represents tens of minutes the second switch represents minutes and the third switch represents tenths of minutes This allows user selectable time cycles from 00 1 minutes to 99 9 minutes in 00 1 minute increments The switches are located in the upper right hand corner Switches Switches Output Hode Figure 2 Back Board Figure 3 Front Board C Modes of Operation An additional feature that is incorporated into the MS2500L transmitter is the ability to monitor and transmit the corrosion potential of the cell This a switch selectable function where the 4 20mA current loop represents a corrosion potential of 1 V positive or 250 mV negative full scale In either mode LPR or OFFSET the user can select two different modes of current loop response The first mode is the normal operation mode or SAMPLE mode This mode is as the one described earlier where
36. th the instrument 1 Check one Repair this instrument under warranty Repair this instrument regardless of problem or cost of repair Inspect the instrument and advise the customer of the approximate cost of repairs if the instrument is not covered under warranty Note This procedure may delay the return of the instru ment to you 2 Instrument Identification Instrument Model Serial Date and Location of Purchase Company s Purchase Order for Original Sale 3 Return the Instrument to Company Name Address Location Telephone Number 4 Description of Trouble a clear description of the problem may shorten repair time 5 Urgency of Repairs 45
37. the current loop information is updated upon the completion ofa measurement cycle This is the logical choice of operation when taking LPR measurements where the current loop information constantly represents the corrosion rate in mils per year This mode of operation can also be used in conjunction with electrode potential measurements where the corrosion potential can be sampled and the current loop updated on intervals as set by the cycle time adjustment The second mode of operation is the TRACK mode In this mode the current loop output is updated every 1 5 seconds When taking corrosion potential measurements this provides the user with a current loop output that constantly tracks the cell corrosion potential For LPR measurements the current loop will reflect the cell response to the applied current This provides an excellent method for selecting the cycle time for the normal mode of operation D Specifications Model MS2500L Loop Powered LPR Transmitter Ordering IN2500L Physical Data Instrument Weight Total Weight w Accessories Instrument Dimensions Case Specifications CENELEC Eexd Mounting Specifications Operating Temperature Storage Temperature Performance Data Measurement Type Range Cycle Time Electrical Data Power Requirements Maximum Probe Cable Distance Output Specifications Special Features 5 02 lb 2 28 Kg 7 08 Ib 3 21 Kg 5 81 H x 4 5 W x 4 81 D
38. therefore unlikely that a single probe location will be able to produce quantita tive corrosion rate data for the overall system Each probe does however provide valuable information by reading the corrosion at the particular location and by indicating the general range of overall corro sion by following changes in corrosion rates caused by adjustments in inhibitors oxygen level or process variables The change in corrosion rate of a system due to altering a variable should be in direct ratio for all parts even though the absolute rates are widely different For instance ifthe addition of an inhibitor will reduce the instrument s reading by 90 percent all normal surfaces of the same metal contacted by the inhibitor should have their corrosion rates similarly reduced Usually a probe location is selected to read on the high side of a system s average rate in order to accentuate changes It should be emphasized that a corrosion rate reading is the actual corrosion rate taking place on the surface of the Test electrode at the time of measurement The condition of the probe s Test electrode surface due to past service as well as current process condi tions may have an important bearing on the readings The corrosion engineer is challenged to adapt the above to his situation and interpret the results In light of the location and operational factors involved E Probe Installation Probe installations should generally be selected on the f
39. tion or environmental service of mild steel electrodes be desired the electrodes need to be removed scrubbed with scouring powder and water and then placed in a beaker of 5 10 percent hydrochloric acid uninhibited until the surfaces are uniformly covered with a layer of hydro gen gas bubbles They should be rinsed thoroughly in clean water before reinstalling This action is usually sufficient to prevent effects of previous service seriously interfering with the new application 13 Circuit Description A Introduction The 52500 is a Linear Polarization Resistance LPR type corrosion monitoring instrument that translates corrosion rates obtained from polarization techniques into a 4 20ma current which is then transmitted through a two wire twisted cable This instrument also incorporates the ability to monitor and transmit the Corrosion Potential obtained from LPR probes using a reference electrode The power for the instrument is supplied on the same two wires that return the corrosion rate signal Therefore to power its internal circuitry the instrument can use no more than the four milliamp live zero current supplied on the loop This 4 20mA type of moni toring instrumentation has become a standard in the process monitoring industry The 4 and 20 milliamp values are used for several reasons 1 A power supply voltage of 25 volts or more can be supplied to overcome long cable drops or to fulfill power requirements for the in
40. tter is housed in explosion proof enclosure with following ratings Housing Ratings Class I Groups B C D Class Groups E F G Class III NEMA 4X FM Approved CSA Approved The MS2500L is equipped with 10 feet of transmitter to probe cable and uses the standard five pin environmental connector found on all of our existing LPR equipment This light armor cable passes into the housing through an explosion proof cable gland Located inside the housing is an electronics package consisting of two printed circuit cards the mount ing bracket for the circuit cards and all the necessary termination points for the cable and current loop connections The termination points on the printed circuit cards are constructed using removable terminal blocks This provides a permanent screw type connection which can break away from the printed circuit cards for their easy removal The printed circuit cards rest in slide rails within the mounting bracket Once the terminal blocks are detached from the printed circuit cards the circuit cards slide out of the instrument for easy repair calibration or replacement B Principle of Operation The MS2500L transmitter reads and stores the potential difference between a reference electrode and a test electrode It then applies a current through an auxiliary electrode and the test electrode until the potential measurement between the test and the reference electrodes changes by 10 millivolts The instrumen
41. uld be equal and the output of AR3 pin 6 should be 100 mV Test the operation of AR1 D this amplifier controls the offset voltage by adjusting the current driven by AR3 Test the operation of the differential amplifier AR4 A The output of AR4 A should be 100 mV Test the operation of the long term sample and hold U13 014 U18 AR9 and 8 During a relax ation cycle the output of should be 100 mV same as the input of AR8 pin 3 If there is an error check the operation of U13 U14 U18 the sample and hold clock U12 pin 13 and the trigger pulse at the end of the polarization cycle U3 pin 13 Test the operation of the short term sample and hold 015 C13 and AR7 During the relaxation cycle the output of AR7 should be at 500mV If there is an error check the operation of the sample and hold gate U15 and the hold pulse U15 pin 13 the hold pulse should only occur during a conver sion cycle of U13 and U14 25 Test the operation of the current loop control circuit AR5 B and Q1 The inputs of ARS B pins 5 and 6 should be equal The voltage drop across R23 will represent the total loop current The difference between the voltage drop across R40 and the voltage drop across R23 will reflect the amount of current required to power the circuitry This current cannot exceed 4mA Erratic or Intermittent Operation This problem is most often caused by faulty switch contacts Again if there is visual evidence of corr
42. which an element or species acquires one or more elec trons thus reducing its valence The transformation of hydrogen ions to atomic hydrogen is an example When reactions of these types occur they never occur in isolation only in pairs or combination In fact the oxidation process which produces more electrons depends on the simultaneous consumption of those electrons by a reduction reaction If no reduction reaction is available no oxidation occurs In these cases the species which undergoes a reduction reaction is called the oxidizing agent The quantitative study of oxidation reduction reactions has resulted in two useful concepts 1 Oxidation reduction potentials which apply to elements and compound 2 Galvanic series which applies to alloys in their environments 41 Oxidation Reduction Potentials The table below is a listing of some useful oxidation reduction potentials These values represent the thermodynamic tendency for the indicated reaction to occur relative basis All potential values are compared to an arbitrary value of 0 00 volts which is assigned to the hydrogen oxidation reaction The more negative a value the more likely the reaction will proceed in the direction shown in table Thus we see that zinc oxidation Zn Zn 2 E 0 763 volts is more likely to occur than iron oxidation Fet 2 E 0 44 volts which in turn is more likely than hydrogen oxidation
43. y be the intention of the user if the instrument is Intended to oper ate only in the OFFSET mode 28 Current Loop Isolation Testing Disconnect the current loop connections from the MS2500L instrument Using a clamp or alligator type connectors connect one end of the 1K ohm resistor to the probe body Connect the positive side of the current loop to the other end of the 1K ohm resistor With the current loop powered up read the voltage drop across the 1K ohm resistor in both AC and DC modes on DVM In either mode there should be less than 10 millivolts to indicate a floating loop Repeat the test using the negative side of the loop If the voltage drop is greater this indicates the presence of a non floating power supply or the current loop monitoring device chart recorder panel meter computer inputs etc is of a grounded or non floating nature If this is the case do not attempt to connect the probe connector to the probe A loop isolator or a repeater power supply such as a MTL 2441 must be used 29 Appendix A Drawings 1 Assembly Drawings Board Overlays 054122 A2 Board Overlays 05A123 O Cable Assembly 8067 Enclosure Assembly 8068 Dimensional Drawing with Field Wiring 8103 2 Installation Drawings MS2500L IN 3300 Transmitter Installation Drawing 8102 30 oes SNOTOIARY BLON PROUD BRLVOIONT est 2 wert bop 4 saowvu
44. zation corrosion rate measurement among these are iron sulfide and hydrocarbons Iron sulfide in the form frequently encountered in some applications is electroni cally conductive Since the Linear Polarization Technique assumes ionic conductiv ity between the electrodes this interferes with the measurements When significant amounts of FeS are present in the system its interference exhibits itself as rapidly increasing corrosion rates until the maximum full scale or unreasonably high level is reached In the opposite way hydrocarbon contamination of Linear Polarization electrodes will effect the readings Usually hydrocarbon coating of the electrodes isolates them from the electrolyte and from electrical communication with each other This results in very low corrosion rate readings 39 Temperature 0 Concentration Fluid Velocity Concentration Suspended Solids Figure 6 Typical Behavior of Corrosion Rate as a Function of Process Variables 40 6 Electrode Potentials Corrosion reactions are a combination of oxidation and reduction reactions Oxidation is the electrochemical process by which an element or species loses electrons and increases its valence state A metal transforming to a metal ion with the simultaneous loss of an electron is an example gt M e 0 0 0 fe Figure 7 Corrosion Reactions Iron Reduction is the electrochemical process by
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