Multi-Electrode Conductivity Analyzers 4621 and 4626

Transcription

1 Operating Instructions IM/4600-MEC Issue 0 Multi-Electrode Conductivity Analyzers 462 and 4626

2 ABB The Company We are an established world force in the design and manufacture of instrumentation for industrial process control, flow measurement, gas and liquid analysis and environmental applications. As a part of ABB, a world leader in process automation technology, we offer customers application expertise, service and support worldwide. We are committed to teamwork, high quality manufacturing, advanced technology and unrivalled service and support. The quality, accuracy and performance of the Company s products result from over 00 years experience, combined with a continuous program of innovative design and development to incorporate the latest technology. The UKAS Calibration Laboratory No is just one of the ten flow calibration plants operated by the Company and is indicative of our dedication to quality and accuracy. EN ISO 900:2000 Cert. No. Q EN 2900 (ISO 900) Lenno, Italy Cert. No. 9/90A Stonehouse, U.K. Electrical Safety 0255 This equipment complies with the requirements of CEI/IEC 600-:200-2 'Safety Requirements for Electrical Equipment for Measurement, Control and Laboratory Use'. If the equipment is used in a manner NOT specified by the Company, the protection provided by the equipment may be impaired. Symbols One or more of the following symbols may appear on the equipment labelling: Warning Refer to the manual for instructions Direct current supply only Caution Risk of electric shock Alternating current supply only Protective earth (ground) terminal Earth (ground) terminal Both direct and alternating current supply The equipment is protected through double insulation Information in this manual is intended only to assist our customers in the efficient operation of our equipment. Use of this manual for any other purpose is specifically prohibited and its contents are not to be reproduced in full or part without prior approval of the Technical Publications Department. Health and Safety To ensure that our products are safe and without risk to health, the following points must be noted:. The relevant sections of these instructions must be read carefully before proceeding. 2. Warning labels on containers and packages must be observed. 3. Installation, operation, maintenance and servicing must only be carried out by suitably trained personnel and in accordance with the information given. 4. Normal safety precautions must be taken to avoid the possibility of an accident occurring when operating in conditions of high pressure and/or temperature. 5. Chemicals must be stored away from heat, protected from temperature extremes and powders kept dry. Normal safe handling procedures must be used. 6. When disposing of chemicals ensure that no two chemicals are mixed. Safety advice concerning the use of the equipment described in this manual or any relevant hazard data sheets (where applicable) may be obtained from the Company address on the back cover, together with servicing and spares information.

3 462 and 4626 Contents Contents INTRODUCTION PREPARATION Checking the Code Number Wall-/Pipe-mounted Instruments Panel-mounted Instruments Conductivity Cells MECHANICAL INSTALLATION Siting Requirements Instruments Conductivity Cells Mounting Wall-/Pipe-mounted Instruments Panel-mounted Instruments Cleaning Epoxy Resin Conductivity Cells Installing the Conductivity Cells Dip-type Cell (Model 222) Flow-line Cell (Model 224) Screw-in Cells (Model 227) Tri Clover Hygienic-fitting Cell (Model 227) DN50 Hygienic-fitting Cells (Model 227) CALIBRATION Equipment Required Preparation Factory Settings Page SIMPLE FAULT FINDING Error Messages No Response to Conductivity Changes Checking the Temperature Input SPECIFICATION Appendix A A. Automatic Temperature Compensation A.. Calculation of Temperature Coefficient A.2 4-Electrode Conductivity System A.3 Effects of Fouling A.4 Practical Conductivity Measurement Notes ELECTRICAL CONNECTIONS Access to Terminals Wall-/Pipe-mounted Instruments Panel-mounted Instruments Connections, General Relay Contact Protection and Interference Suppression Wall-/Pipe-mounted Instrument Connections Panel-mounted Instrument Connections Selecting the Mains Voltage Wall-/Pipe-mounted Instruments Panel-mounted Instruments Conductivity Cell Connections CONTROLS AND DISPLAYS Displays Control Familiarization OPERATION Instrument Start-up Operating Page PROGRAMMING Access to Secure Parameters Language Page Set Up Parameters Page Set Up Alarms Page Set Up Retransmission Page Output Functions Bi-linear Output...26 IM/4600-MEC Issue 0

4 462 and 4626 INTRODUCTION INTRODUCTION The 462 wall-/pipe-mounting and 4626 panel mounting conductivity transmitters have been designed to work specifically with multi-electrode conductivity cells to provide reliable performance of high level conductivity liquids. Both instruments have a single programmable conductivity input channel with built-in temperature compensation. When making temperature compensated measurements the sample temperature is sensed by a Pt000 resistance thermometer mounted in the measuring cell. Remote range-change versions are available for switching the display range between two pre-defined ranges using a remote switch. Instrument operation and programming is via four tactile membrane switches located on the front panel. Programmed functions are protected from unauthorized alteration by a five-digit security code. 2 PREPARATION 2. Checking the Code Number 2.. Wall-/Pipe-mounted Instruments 462/ /500 SP5 462/500 SP9 462/500 SP28 Standard Remote range-change versions: 0 0mS/cm and 0 00mS/cm 0 20mS/cm and 0 200mS/cm 0 25mS/cm and 0 250mS/cm millisiemens/cm A A millisiemens/cm A A Fig. 2. Checking the Code Number (Model Wall-/pipe-mounted) 2..2 Panel-mounted Instruments 00m Max. 3 Slide instrument out of case Screw-in Type 2 Undo captive screw Dip-type Remove plug (if fitted) Flow-line Type 4626/ /500 SP5 4626/500 SP9 4626/500 SP28 Standard Remote range-change versions: 0 0mS/cm and 0 00mS/cm 0 20mS/cm and 0 200mS/cm 0 25mS/cm and 0 250mS/cm Fig.. System Schematic Fig. 2.2 Checking the Code Number (Model Panel-mounted) 2 IM/4600-MEC Issue 0

5 462 and PREPARATION 2..3 Conductivity Cells Basic Type No. Mounting & Version Constant (K) Process Connection Type Temperature Compensation Code Characters,2 3,4, Electrolytic conductivity measuring cell 2 Dip Type (Epoxy Resin) Epoxy Stem Stainless Steel Stem 5 Pt000 Resistance Thermometer Model 222 Basic Type No. Mounting & Version Constant (K) Process Connection Type Temperature Compensation Code Characters,2 3,4, Model Electrolytic conductivity measuring cell 4 Flowline (Epoxy Resin) in BSP 8 2in NPT 5 Pt000 Resistance Thermometer Screw-in type Basic Type No. Mounting & Version Constant (K) Process Connection Type Temperature Compensation Tri Clover Code Characters,2 3,4, DN50 22 Electrolytic conductivity measuring cell 7 Screw-in (Epoxy Resin) in BSP 5 Pt in Tri Clover 3 DN50 8 in NPT Resistance Thermometer Model 227 Fig. 2.3 Checking the Conductivity Cell Code Number IM/4600-MEC Issue 0 3

6 462 and MECHANICAL INSTALLATION 3 MECHANICAL INSTALLATION 3. Siting Requirements 3.. Instruments 3..2 Conductivity Cells Caution. Mount in a location free from excessive vibration. Mount away from harmful vapors and/or dripping fluids. Note. It is preferable to mount the instrument at eye level, allowing an unrestricted view of the front panel displays and controls. Caution. Ensure that the integral cable (where applicable) does not hang against hot or abrasive objects when the plug is connected to the bulkhead socket. Note. Allow sufficient clearance for easy removal of cell for cleaning - see Section 3.4 for overall dimensions of cells. Maximum Distance 00m Conductivity Cell A Maximum Distance of Instrument to Cell Model Max. Temperature ( C) A Maximum Temperature Limits 20 C Min. 55 C Max. Model Max. Pressure (p.s.i.) NA B Within Temperature Limits B Maximum Pressure Limits IP66 Acid 6% Concentration C Within Environmental Limits Alkali 8% Concentration Fig. 3. Siting Requirements - Instrument C Acid/Alkali Concentration Limits Fig. 3.2 Siting Requirements - Conductivity Cell 4 IM/4600-MEC Issue 0

7 462 and MECHANICAL INSTALLATION 3.2 Mounting 3.2. Wall-/Pipe-mounted Instruments Dimensions in mm (in) 60 (6.3) 68 (2.68) 42 (.65) 250 (9.84) 24 (8.43) Fixing Centers 232 (9.3) 69 (2.72) Fixing Centers 200 (7.9) Allowance for Cable Bends 6 (2 3 / 8 ) O.D. Vertical or Horizontal Post Fig. 3.3 Overall Dimensions 2 Drill suitable holes Position plates over U bolts Position U bolts on pipe 2 Mark fixing centres (see Fig. 3.3) 3 Secure plates 3 Secure instrument to wall using suitable fixings A Wall-mounting 4 Secure transmitter to mounting plate B Pipe-mounting Fig. 3.4 Wall-/Pipe-mounting IM/4600-MEC Issue 0 5

8 462 and MECHANICAL INSTALLATION Panel-mounted Instruments Dimensions in mm (in) 96 (3.78) 2 (0.47) 9 (7.52) (3.62 ) 96 (3.78) Panel Cut-out (3.62 ) Fig. 3.5 Overall Dimensions Cut a hole in the panel (see Fig. 3.5 for dimensions). Instruments may be close stacked to DIN Insert the instrument into the panel cut-out. 4 Loosen the retaining screw on each panel clamp. 2 3 Remove the panel clamp and anchors from the instrument case Refit the panel clamps to the case, ensuring that the panel clamp anchors are located correctly in their slot. Secure the instrument by tightening the panel clamp retaining screws see Caution. Fig. 3.6 Panel Mounting Caution. The clamp must fit flat on the instrument casing. If the clamp is bowed, the securing screw is overtight and sealing problems may occur. 6 IM/4600-MEC Issue 0

9 462 and MECHANICAL INSTALLATION 3.3 Cleaning Epoxy Resin Conductivity Cells Before installing a conductivity cell, clean the electrodes as follows. Thoroughly clean the electrode bore with a nylon-bristle brush (supplied) and a warm detergent solution. For more tenacious deposits a 2% hydrochloric acid solution may be used. After cleaning, thoroughly rinse the cell with distilled water and view the bore against a bright light to ensure that the interior surfaces are evenly wetted, i.e. free from grease deposits. Avoid wetting the electrical connection terminals Flow-line Cell (Model 224) Caution. Do not overtighten. Overtightening may result in damage to the cell body. Dimensions in mm (in) /2in BSP Parallel or NPT Thread * 3.4 Installing the Conductivity Cells Caution. After cleaning and installing a conductivity cell ensure it remains filled with liquid and is not allowed to dry out Dip-type Cell (Model 222) 36.5 ( 7 / 6 ) 92 (3 5 / 8 ) 32 ( / 4 ) Caution. Ensure that the electrode bore remains fully immersed at minimum fluid levels. 46 (5 3 / 4 ) Dimensions in mm (inches) 65 (2 / 2 ) 44 ( 3 / 4 ) 0233/820 Cable 6.m (20ft) long * For /2in BSP process connections a /2in BSP parallel thread must be used. A Overall Dimensions (29) Slide to required position 3 Form bracket to hook over edge of tank Apply PTFE tape to pipe and screw into celll 38. (5.437) 2 Ensure lower end of cell is immersed in sample fluid 28.6 (.25) 2 Secure the cell to any adjacent flat surface using the two /4in BSW screws supplied Fig. 3.7 Dip-type Cell B Installation Fig. 3.8 Flow-line Cell IM/4600-MEC Issue 0 7

10 462 and MECHANICAL INSTALLATION Screw-in Cells (Model 227) Dimensions in mm (in) 23.7 (9 / 8) 60.3 (6 5 / 6 ) 57. (2 / 4 ) Apply PTFE tape 28.6 ( / 8 ) 89.0 (3 / 2) in. BSP Thread or in NPT Thread A Overall Dimensions 2 Screw cell directly into pipeline or ready-mounted female bush B Installation Fig. 3.9 Screw-in Cells Tri Clover Hygienic-fitting Cell (Model 227) DN50 Hygienic-fitting Cells (Model 227) Dimensions in mm (in) Dimensions in mm (in) 23.7 (9 / 8 ) 23.7 (9 / 8 ) 60.3 (6 5 / 6 ) 57. (2 / 4 ) 60.3 (6 5 / 6 ) 57. (2 / 4in) 28.6 ( / 8 ) 63 ( / 2 ) 89.0 (3 / 2 ) ( / 8 ) (3 / 2 ) 89.0 (3 / 2 ) Fig. 3.0 Tri Clover Hygienic Fitting Cell Fig. 3. DN 50 Hygienic Fitting Cell 8 IM/4600-MEC Issue 0

11 462 and ELECTRICAL CONNECTIONS 4 ELECTRICAL CONNECTIONS Warning. Before making any connections, ensure that the power supply, any high voltage-operated control circuits and high common mode voltages are switched off. 4. Access to Terminals 4.. Wall-/Pipe-mounted Instruments Remove protection cover 4 Slide down 2 Pull out slightly Slacken captive screws 3 2 and slide off Earth Studs Fig. 4. Access to Terminals - Wall-/Pipe-mounted Instruments 4..2 Panel-mounted Instruments Remove nuts and protection cover 2 Remove mains cover Mains Cover Fig. 4.2 Access to Terminals - Panel-mounted Instruments IM/4600-MEC Issue 0 9

12 462 and ELECTRICAL CONNECTIONS 4.2 Connections, General Note. Earthing (grounding) - stud terminal(s) is fitted to the transmitter case for bus-bar earth (ground) connection - see Fig. 4. or Fig Cable lengths - the integral cable may be extended using a suitable junction box, but the total cable length must not exceed 00m. Cable routing - always route signal output/conductivity cell cable leads and mains-carrying/relay cables separately, ideally in earthed (grounded) metal conduit. Employ twisted pair output leads or use screened cable with the screen connected to the case earth stud. Ensure that the cables enter the transmitter through the glands nearest the appropriate screw terminals and are short and direct. Do not tuck excess cable into the terminal compartment. Cable glands & conduit fittings - ensure a moisture-tight fit when using cable glands, conduit fittings and blanking plugs/bungs (M20 holes). The M6 glands ready-fitted to wall-mounted instruments accept cable of between 4 and 7mm diameter. Relays - the relay contacts are voltage-free and must be appropriately connected in series with the power supply and the alarm/control device which they are to actuate. Ensure that the contact rating is not exceeded. Refer also to Section 4.2. (below) for relay contact protection details when the relays are to be used for switching loads. Retransmission output - Do not exceed the maximum load specification for the selected current retransmission range - see section 0, page 32 Since the retransmission output is isolated the -ve terminal must be connected to earth (ground) if connecting to the isolated input of another device Relay Contact Protection and Interference Suppression If the relays are used to switch loads on and off, the relay contacts can become eroded due to arcing. Arcing also generates radio frequency interference (RFI) which can result in instrument malfunctions and incorrect readings. To minimize the effects of RFI, arc suppression components are required; resistor/capacitor networks for a.c. applications or diodes for d.c. applications. These components can be connected either across the load or directly across the relay contacts. On 4600 Series instruments the RFI components must be fitted to the relay terminal block along with the supply and load wires - see Fig For a.c. applications the value of the resistor/capacitor network depends on the load current and inductance that is switched. Initially, fit a 00R/0.022μF RC suppressor unit (part no. B9303) as shown in Fig. 4.3A. If the instrument malfunctions (incorrect readings) or resets (display shows 88888) the value of the RC network is too low for suppression an alternative value must be used. If the correct value cannot be obtained, contact the manufacturer of the switched device for details on the RC unit required. For d.c. applications fit a diode as shown in Fig. 4.3B. For general applications use a IN5406 type ( 600V peak inverse voltage at 3A - part no. B7363) Note. For reliable switching the minimum voltage must be greater than 2V and the minimum current greater than 00mA. NC C NO Relay Contacts NC C NO Relay Contacts Diode R C External L A.C. Supply N Load External + D.C. Supply Load Fig. 4.3 Relay Contact Protection 0 IM/4600-MEC Issue 0

13 462 and ELECTRICAL CONNECTIONS 4.3 Wall-/Pipe-mounted Instrument Connections Note. Refer to Fig. 4. for Access to Terminals. Caution. Slacken terminal screws fully before making connections. 2 3 NC C NO N L NC C NO Cell Connections (Serial or Remote Range-change Versions only) Current Retrans. Relay Relay 2 Power Supply Cell Connections Serial RS422/RS485 Retransmission Relay Relay 2 Power Supply Brown Green/Yellow Black Red Blue Link 2 Braids (screens) see Note below Cable 0233/ Tx 0V Rx+ Rx Tx+ Tx 0V or Remote Range-change Output + Range (Lower) Retrans. Output Relays NC C Relay NO NC C Relay 2 NO NC C NO = = = Normally Closed Common Normally Open Mains Supply N L Neutral Line Earth Earth Stud (on case) see Warning below and Fig. 4. Range 2 (Upper) 2nd Retransmission Output 4 5 ve +ve Refer to Table 4. overleaf for terminal descriptions Fig. 4.4 Wall-/Pipe-mounted Instrument Connections Warning. The power supply earth (ground) must be connected to ensure safety to personnel, reduction of the effects of RFI interference and correct operation of the power supply interference filter. Note. On applications where the sample is fully isolated from earth, the conductivity cable screens must be connected to earth either at the instrument (terminal 7) or at the cell, but not both. Refer to Fig. 4.8 for conductivity cell connections. IM/4600-MEC Issue 0

14 462 and ELECTRICAL CONNECTIONS 4.4 Panel-mounted Instrument Connections Note. Refer to Fig. 4.2 for Access to Terminals. Caution. Slacken terminal screws fully before making connections. Earth Stud TBA E N L TBB Remote Range-change Versions only Retransmission Output Relay Relay 2 Mains Supply + Normally Closed Common Normally Open Normally Closed Common Normally Open Neutral Live E N L V RS422/ Rx RS485 Rx+ Serial or Tx Versions Tx+ Only 2 Braids (screens) see Note Blue below Red Black Green/Yellow Brown 4 Range 2 (Upper) Cable 0233/820 Range (Lower) 2 nd Retransmission Output (if fitted) 4 ve 5 +ve Refer to Table 4. below for terminal descriptions Earth see Warning below Earth Stud (on case) Fig. 4.5 Panel-mounted Instrument Connections Warning. The power supply earth (ground) must be connected to ensure safety to personnel, reduction of the effects of RFI interference and correct operation of the power supply interference filter. Connect the earth lead directly to the case earth stud and not to the 'E' terminal. Note. On applications where the sample is fully isolated from earth, the conductivity cable screens must be connected to earth either at the instrument (terminal 6) or at the cell, but not both. Refer to Fig. 4.8 for conductivity cell connections. Instrument Type Terminal Number Wall-mounted Panel-mounted Current electrode Guard electrode Voltage electrode Voltage electrode PT000 input Link to 7 (6) PT000 input & earth electrode Table 4. Conductivity Cell Terminal Descriptions 2 IM/4600-MEC Issue 0

15 462 and ELECTRICAL CONNECTIONS 4.5 Selecting the Mains Voltage 4.5. Wall-/Pipe-mounted Instruments Note. Use a small, flat-bladed screwdriver to remove the screw cap from the case. Remove front panel 4 3 Remove cap and screw Slacken captive screws and remove protection cover Select the mains voltage required 230V Remove front panel screws 5V Remove cover (see Fig. 4.) Fig. 4.6 Selecting the Mains Voltage - Wall-/Pipe-mounted Instruments Panel-mounted Instruments 3 Slide instrument out of case 2 Undo captive screw 5 Remove plug (if fitted) 4 Select the mains voltage required 5V 230V 5 5 Fig. 4.7 Selecting the Mains Voltage - Panel-mounted Instruments IM/4600-MEC Issue 0 3

16 462 and ELECTRICAL CONNECTIONS 4.6 Conductivity Cell Connections Note. Use only the recommended 0233/820 cable. The cable screens must be connected to Earth either at the instrument or at the cell, but not both. Refer to Fig. 4.4 and Fig. 4.5 for instrument connections. Ensure braids are insulated and do not touch any other terminals or metal parts Braids (screens) Blue Red Black Green / Yellow Brown 0233/820 cable see Note Model 227 Blue 2 Braids (screens) Black Brown Green/Yellow Red 0233/820 cable see Note Model 224 Fig. 4.8 Conductivity Cell Connections 4 IM/4600-MEC Issue 0

17 462 and CONTROLS AND DISPLAYS 5 CONTROLS AND DISPLAYS 5. Displays The display comprises a 5-digit, 7-segment digital upper display line and a 6-character dot-matrix lower display line. The upper display line shows actual values of conductivity, temperature, alarm set points or programmable parameters. The lower display line shows the associated units or programming information. 5.2 Control Familiarization Page Parameter Parameter 2 Parameter 3 Parameter 4 Advance to next page or For majority of parameters A Advancing to Next Page Page 2 Parameter Parameter 2 Parameter 3 Upper Display Line Lower Display Line 50.0 millisiemens/cm Advance to next parameter Page X Parameter Parameter 2 Parameter 3 Parameter 4 B Moving Between Parameters Alarm LEDs Parameter Value Adjust Membrane Keys or New value is automatically stored C Adjusting and Storing a Parameter Value Fig. 5. Location of Controls and Displays Parameter X Y Z Select or New value is automatically stored D Selecting and Storing a Parameter Choice Fig. 5.2 Membrane Key Functions IM/4600-MEC Issue 0 5

18 462 and OPERATION 6OPERATION 6. Instrument Start-up Ensure all electrical connections have been made correctly and switch on. 6.2 Operating Page The Operating Page is a general use page in which parameters are viewed only and cannot be altered. To alter or program a parameter refer to the programming pages in Section %NaOH (w/w) or %H2S04 (w/w) or %HCl (w/w) or millisiemens/cm Measured Value and Units The conductivity or concentration value is displayed on the upper display line and the conductivity or concentration units on the lower display line. The units are displayed as any of the following: % Sodium Hydroxide (NaOH) % Sulphuric (H2SO4) % Hydrochloric (HCl) millisiemens per centimeter The units are programmable within the limits detailed in Section 7.3, Set Up Parameters Page. Note. On instruments fitted with a remote range-change facility, the units are preset to millisiemens/cm and cannot be changed. Press to advance to next page or SECURITY CODE These two keys are used to advance to all subsequent parameters and pages. Press to advance to next parameter 25.0 Temperature ( C) Sample Temperature The sample temperature is displayed in either ºC or ºF. The display units are programmable - see section 7.3, page 9, Set Up Parameters Page Alarm Setpoint If alarm 2 is set for cell fouling Alarm Set Point The set point value and relay/l.e.d. action are programmable - see section 7.4, page 2, Set Up Alarms Page Alarm 2 Setpoint Alarm 2 Set Point The set point value and relay/l.e.d. action are programmable - see section 7.4, page 2, Set Up Alarms Page SECURITY CODE Advance to Access to Secure Parameters on page 8. 6 IM/4600-MEC Issue 0

19 462 and PROGRAMMING 7 PROGRAMMING Note. All parameter values shown on the upper display are the Company standard settings. Alarm 2 Action Set to Foul Operating Page Section 6.2, Page %NaOH (w/w) Set Up Parameters Page Section 7.3, Page8 SET UP PARAMETER %H2SO4 (w/w) %HCL (w/w) millisiemens/cm Not Displayed on Instruments Fitted with Remote Range-Change Facility 250 Temperature ( C) 8.00 Alarm Setpoint 2.00 Alarm 2 Setpoint Secure Parameters Access to Secure Parameters Section 7., Page SECURITY CODE Remote Rangechange Version Standard Version Units NaOH HCL. ms/cm Display Span Temp Comp Yes Yes. H2SO No 20 Temp Coefficient Ref Temp 25 C 20 C Temp Units ( C) ( F) Language Page Section 7.2, Page 8 Espanol Francais Deutsch Cable Comp Yes Yes No 50 Cable Length(m) English If NaOH, H2SO4 or HCL Fail or Off Fail or Off Set Up Alarms Page Section 7.4, Page 20 SET UP ALARMS A Type Fail Temp Cond Off A Action High A Setpoint Low 8.00 A2 Type Foul Fail Temp Cond Off A2 Action High A2 Setpoint Low Alter Sec. Code Set Up Retransmission Page Section 7.5, Page 22 SET UP RETRANS Set Up Retrans 2 Set Up Retrans RTX Type RTX Type RTX. Linear Bi-Linear Span Input 00% 0% 00. Enter Input (%) 500. Enter Output (%) 000. RTX Span (UNITS) Cond RTX O/P Temp Cond RTX. Linear Bi-Linear Span Input 00% 0% 00. Enter Input (%) 500. Enter Output (%) 000. RTX Span (UNITS). 00 RTX Zero (UNITS) 00. Test Retrans (%) Operating Parameters Secure Parameters Available only on 462/800 and 4626/800 instruments Factory Settings Page Section 8.3, Page 27 FACTORY SETTINGS FACTORY SET CODE ELECTRICAL CAL Calibrate Yes Yes No xxxxx Res Zero (O/C) xxxxx Res Span (0k) xxxxx Res Zero 2 (O/C) xxxxx Res Span 2 (k0) xxxxx Res Zero 3 (O/C) xxxxx Res Span 3(00R) xxxxx Temp Zero (00R) xxxxx Temp Span (50R) Adjust RTX Zero Adjust RTX Span Adjust RTX Zero2 Adjust RTX Span Alter Fact. Code No Fig. 7. Overall Programming Chart IM/4600-MEC Issue 0 7

20 462 and PROGRAMMING 7. Access to Secure Parameters SECURITY CODE SET UP PARAMETERS Security Code Enter the required code number, between and 9999, to gain access to the secure parameters. If an incorrect value is entered, access to subsequent programming pages is prevented and the display reverts to the Operating Page. Advance to Language Page. 7.2 Language Page Espanol Francais Deutsch English Language Page Select the language to be displayed on all subsequent pages SET UP PARAMETER Advance to Set Up Parameters Page. 8 IM/4600-MEC Issue 0

21 462 and PROGRAMMING 7.3 Set Up Parameters Page SET UP PARAMETER Remote Range-change Units Display Span Standard ---- Display Span NaOH H2SO4 HCl ms/cm 8.00 Press to advance to next parameter or press to advance to next page. These two keys are used to advance to all subsequent parameters and pages. If a parameter is changed it is automatically stored on operation of either key. Conductivity Units The conductivity units can be programmed to suit the range and application required. Select the required units: NaOH - sodium hydroxide H2SO4 - sulphuric acid HCl - hydrochloric acid ms/cm - millisiemens/cm Display Span (Full Scale) Set the full scale value required, within the limits: NaOH to 8.00% at 50ºC or 2.00 to 5.00% at 00ºC H2SO to 6.00% at 50ºC HCl to 6.00% at 50ºC ms/cm to at 00ºC 5.0 to at 50ºC Display Span (Remote Range-Change Versions Only) The display spans of the upper and lower ranges are preset during manufacture and cannot be adjusted: Order Code Suffix Lower Range Upper Range SP5 SP9 SP28 0 to 0mS/cm 0 to 20mS/cm 0 to 25mS/cm 0 to 00mS/cm 0 to 200mS/cm 0 to 250mS/cm The upper and lower ranges are selected by means of an external switch - see Fig. 4.4 and Fig The full scale display span of the selected range is displayed. Continued on next page. IM/4600-MEC Issue 0 9

22 462 and PROGRAMMING If NaOH, H2SO4 or HCL selected Temp Comp No Yes Yes No 2.0 Temp Coefficient Temperature Compensation for fluctuations in the sample temperature can be switched in or out, as required. Select Yes to switch in or No to switch out. Temperature Coefficient If unknown, the temperature coefficient ( ) of the solution can be calculated - see section A.., page 35. Enter the temperature coefficient ( ) of the solution (0.5 to 2.5). If the value has not yet been calculated, provisionally set it to 2%/ºC. Note. If concentration units are selected, Temperature Coefficient is automatically programmed. Ref Temp 25 C Temp Units ( C) ( F) Reference Temperature Enter the required reference temperature as either 25ºC (77ºF) or 20ºC (68ºF). Note. Applies only when ms/cm is selected. Temperature Units The sample temperature (and reference temperature) can be displayed as either degrees Fahrenheit or Celsius. Select either ºC or ºF. Cable Comp. Yes No Cable Compensation To improve temperature measuring accuracy with a 2-wire Pt000 Resistance Thermometer measuring system, cable length compensation is required. 50 Cable Length (m) Cable Length Enter the approximate cable length within ±2m. Return to top of page SET UP ALARMS Advance to Set Up Alarms Page. 20 IM/4600-MEC Issue 0

23 462 and PROGRAMMING 7.4 Set Up Alarms Page SET UP ALARMS or - press to advance to next parameter - press to advance to next page. Fail or Off A Type Fail Temp Cond Off These two keys are used to advance to all subsequent parameters and pages. If a parameter is changed it is stored automatically on operation of either key. Alarm Type Select the type of alarm required. For Fail, Temp and Cond alarm types, the alarm l.e.d. is off and the relay energized during normal conditions. In a fail condition, the l.e.d. is on and the relay de-energized. Fail - The instrument alerts the operator to either a power failure or a condition that causes any of the error messages listed in Table 9. to be displayed. Temp - The instrument alerts the operator if the temperature of the process fluid exceeds or drops below the value set in the Alarm Set Point parameter, depending on the type of Alarm Action selected below. Cond - The instrument alerts the operator if the conductivity of the process fluid exceeds or drops below the value set in the Alarm Set Point parameter, depending on the type of Alarm Action selected below. Off - If selected, no alarms are set and the alarm l.e.d. is off and the relay de-energized at all times. A Action High Low Alarm Action For 'Fail-safe' alarm operation the relay's alarm state must be the same as the power-down state, i.e. the relay is de-energised. For High alarm operation the relay must be energized below the alarm set point. For Low alarm operation the relay must be energized above the alarm set point. The alarm l.e.d.s are illuminated in the alarm condition. Select the required alarm action from the following table: Alarm Action LED Condition for Input Above Set Point LED Condition for Input Below Set Point Relay Condition for Input Above Set Point Relay Condition for Input Below Set Point High ON OFF De-energized Energized Low OFF ON Energized De-energized The set point band is defined as the actual value of the set point plus or minus the hysteresis value. The hysteresis value is ± % of the Alarm set point value. Alarm action occurs if the input value is above or below the set point band. If the input moves within the set point band the last alarm action is maintained. A Setpoint 800. Alarm Set Point The alarm set point can be set to any value within the input range being displayed. The set point value is subject to hysteresis as detailed above. Set the alarm set point to the required value. Continued on next page. IM/4600-MEC Issue 0 2

24 462 and PROGRAMMING Foul, Fail or Off A2 Type A2 Action 800. A2 Setpoint Foul Fail Temp Cond Off High Low Alarm 2 Type Repeat as for Alarm Type on previous page. Foul - The instrument alerts the operator when the probe needs cleaning. Alarm 2 Action Repeat as for Alarm Action on previous page. Alarm 2 Set Point Repeat as for Alarm Set Point on previous page Alter Sec. Code Alter Security Code Set the security code to a value between and Return to top of page SET UP RETRANS Advance to Set Up Retransmission Page. 22 IM/4600-MEC Issue 0

25 462 and PROGRAMMING 7.5 Set Up Retransmission Page SET UP RETRANS or - press to advance to next parameter - press to advance to next page. These two keys are used to advance to all subsequent parameters and pages. If a parameter is changed it is stored automatically on operation of either key. Set Up Retrans Set Up Retransmission RTX Type Retransmission Output Range Set the retransmission output current range for retransmission channel. Rtx. Linear Bi-Linear Linear Bi-linear Retransmission Output Scale Select the retransmission output scale required. Linear Bi-Linear - see section 7.6, page 26, Fig. 7.2 Note. The output scale is calculated as a percentage of the retransmission output span. Ensure that the retransmission output span has been set correctly - see below. Span Input 00% 0% 00. Enter Input (%) Span Input Set the percentage of the display span over which the output is to be scaled to 00 or 0%. This is Point A on Fig Enter Input % Set the percentage of the display span at which the breakpoint occurs to between 0. and 00% in 0.% increments. This is Point B on Fig Enter Output (%) 000. RTX Span (Units) Enter Output % Set the percentage output at which the breakpoint occurs to between 0.0 and 00% in 0.% increments. This is Point C on Fig Set the alarm type to the required setting. Retransmission Span Set the required span over which the retransmission output is to operate to between 0 and 00% of the display span - see section 7.3, page 9, Set Up Parameters Page. Continued on next page. IM/4600-MEC Issue 0 23

26 462 and PROGRAMMING Set Up Retrans 2 Set Up Retransmission 2 Note. Available only on 462/800 and 4626/800 instruments. RTX Type Retransmission 2 Output Range Set the retransmission output current range for retransmission channel 2. Temp RTX O/P Temp Cond Retransmission 2 Output Assignment Select the Retransmission output required: Temp Cond - - Temperature Conductivity Advance to RTX Span (Units) Rtx. Linear Bi-Linear Linear Bi-linear Retransmission 2 Output Scale Select the retransmission output scale required. Linear Bi-Linear - see see section 7.6, page 26, Fig. 7.2 Note. The output scale is calculated as a percentage of the retransmission 2 output span. Ensure that the retransmission 2 output span has been set correctly - see overleaf. Span Input 00% 0% 00. Enter Input (%) 500. Enter Output (%) Span Input Set the percentage of the display span over which the output is to be scaled - 00 or 0%. This is Point A on Fig Enter Input % Set the percentage of the display span at which the breakpoint occurs - 0. to 00% in 0.% increments. This is Point B on Fig Enter Output % Set the percentage output at which the breakpoint occurs to 00% in 0.% steps. This is Point C on Fig Set the alarm type to the required setting. Continued on next page. 24 IM/4600-MEC Issue 0

27 462 and PROGRAMMING 000. RTX Span (Units) Retransmission 2 Span Set the required span over which the retransmission output is to operate to between 0 and 00% of the display span - see section 7.3, page 9, Set Up Parameters Page. Cond Temp 00. RTX Zero (Units) Retransmission 2 Zero Set the zero point for the retransmission 2 output - see Table Test Retrans (%) Test Retransmission Output The instrument automatically transmits a test signal of 0, 25, 50, 75 or 00% of the retransmission range selected above. The % test signal selected is shown on the upper display. Example - for a selected range of 0 to 20mA and 50% retransmission test signal, 0mA is transmitted. Select the required retransmission test signal. Return to top of page FACTORY SETTINGS Advance to Factory Settings Page. Retransmission 2 Output Assignment Retransmission 2 Span Retransmission 2 Zero Conductivity Programmable between 0 and 00% of display span Set automatically according to selected Retransmission Output 2 Scale: Linear Bi-linear = = 0 0 Temperature (ºC) 00 (max.) 0 (min.) (subject to minimum range of 20ºC) Temperature (ºF) 22 (max.) 32 (min.) (subject to minimum range of 36ºF) Table 7. Retransmission 2 Zero IM/4600-MEC Issue 0 25

28 462 and PROGRAMMING 7.6 Output Functions 7.6. Bi-linear Output 00 A % Retransmission Output C % B Conductivity Measurement shown as % of Display Span Fig. 7.2 Bi-linear Output 26 IM/4600-MEC Issue 0

29 462 and CALIBRATION 8 CALIBRATION Note. The instrument is calibrated by the Company prior to despatch and recalibration should be carried out only if the instrument's accuracy is suspect and suitably calibrated test equipment is available. 8. Equipment Required. Decade resistance box (conductivity cell simulator): 0 to 0kΩ (in increments of 0.0Ω), accuracy ±0.%. 2. Decade resistance box (PT000 simulator): 0 to kω (in increments of 0.Ω), accuracy ±0.%. 3. Digital milliammeter (current output measurement): 0 to 20mA. Note. Resistance boxes have an inherent residual resistance which may range from a few mω up to Ω. This value must be taken into account when simulating input levels, as should the overall tolerance of the resistors within the boxes. 8.2 Preparation. Switch off the supply and disconnect the conductivity cell and PT000 from the instrument's terminal blocks - see Fig. 4.4 or Fig Wall-mounted Instruments (Fig. 8.A): a. Link terminals & 3, 4 & 7, 6 & 7. b. Connect terminal 7 (or 6) to the case earth stud. c. Connect a 0Ω resistor between terminals 2 & 7. (See note below). d. Connect the 0 to 0kΩ decade resistance box between terminals 3 & 4 to simulate the conductivity cell. Connect the decade box earth to the case earth stud. e. Connect the 0 to kω decade resistance box between terminals 5 & 7 to simulate the PT000. f. Connect the milliammeter to the retransmission output terminals - see Fig Panel-mounted Instruments (Fig. 8.B): a. Link terminals 6 & 7, 6 & 9, 0 & 2. b. Connect terminal 6 (or 7) to the case earth stud. c. Connect a 0Ω resistor between terminals 6 &. (See note below). d. Connect the 0 to 0kΩ decade resistance box between terminals 9 & 0 to simulate the conductivity cell. Connect the decade box earth to the case earth stud. e. Connect the 0 to kω decade resistance box between terminals 6 & 8 to simulate the PT000. f. Connect the milliammeter to the retransmission output terminals - see Fig Switch on the supply and allow ten minutes for the circuits to stabilize. 5. Select the 'FACTORY SETTINGS' page and carry out - see section 8.3, page 29. Note. The 0Ω resistor is used to provide an equivalent cell loading for the guard electrode circuit (see Appendix A4), and must be fitted to ensure optimum calibration accuracy. IM/4600-MEC Issue 0 27

30 462 and CALIBRATION Decade Resistance Box Connections TBB Conductivity Cell Simulator Conductivity Cell Simulator PT000 Simulator PT000 Simulator Decade Resistance Box Connections PT000 Simulator PT000 Simulator Conductivity Cell Simulator Case Earth Stud 0Ω Conductivity Cell Simulator 0 0Ω Terminal links Case Earth Stud 2 Terminal links A Wall-/Pipe-mounted Instruments A Panel-mounted Instruments Fig. 8. Instrument Terminal Links and Decade Resistance Box Connections 28 IM/4600-MEC Issue 0

31 462 and CALIBRATION 8.3 Factory Settings Page When carrying out the electrical calibration procedure, the actual values denoted by 'xxxxx' are unimportant and are used only to determine display reading stability. FACTORY SETTINGS FACTORY SET CODE Factory Settings Access Code Enter the required code number, between and 9999, to gain access to the factory settings. If an incorrect value is entered, access to subsequent parameters is prevented and the display reverts to the top of the Factory Settings Page. ELECTRICAL CAL Calibrate Yes No No Yes Advance to Adjust RTX Zero xxxxx Res Zero (O/C) Electrical Calibration Select Yes to access the electrical calibration sequence. Select 'No' to advance to Adjust Retransmission Zero. Caution. Do not select 'Yes' unless instrument calibration is required. Advance to next parameter. Calibrate Zero Open circuit the cell simulator and allow the instrument display to stabilize. Advance to next parameter. xxxxx Res Span (4R) Calibrate Span Set the cell simulator to 4Ω and allow the instrument display to stabilize. xxxxx Res Zero 2 (O/C) Advance to next parameter. Calibrate Zero 2 Open circuit the cell simulator and allow the instrument display to stabilize. xxxxx Res Span 2 (8R) Advance to next parameter. Calibrate Span 2 Set the cell simulator to 8Ω and allow the instrument display to stabilize. xxxxx Res Zero 3 (O/C) Advance to next parameter. Calibrate Cell Zero 3 Open circuit the cell simulator and allow the instrument display to stabilize. Advance to next parameter. Continued on next page. IM/4600-MEC Issue 0 29

32 462 and CALIBRATION xxxxx Res Span 3 (40R) xxxxx Temp Zero (K0) xxxxx Temp Span (k5) Adjust RTX Zero Calibrate Cell Span 3 Set the cell simulator to 40Ω and allow the instrument display to stabilize. Advance to next parameter. Calibrate Temperature Zero Set the temperature simulator to kω and allow the instrument display to stabilize. Advance to next parameter. Calibrate Temperature Span Set the temperature simulator to.5kω and allow the instrument display to stabilize. Advance to next parameter. Adjust Retransmission Zero Set the milliammeter reading to 4mA. Note. The retransmission range selected in the Set Up Retransmission Page does not affect the reading. Adjust RTX Span Advance to next parameter. Adjust Retransmission Span Set the milliammeter reading to 20mA. Note. The retransmission range selected in the Set Up Retransmission Page does not affect the reading. Adjust RTX Zero2 Advance to next parameter. Adjust Retransmission 2 Zero (available only on 462/800 and 4626/800 instruments) Set the milliammeter reading to 4mA. Note. The retransmission range selected in the Set Up Retransmission Page does not affect the reading. Adjust RTX Span2 Advance to next parameter. Adjust Retransmission 2 Span (available only on 462/800 and 4626/800 instruments) Set the milliammeter reading to 20mA. Note. The retransmission range selected in the Set Up Retransmission Page does not affect the reading Alter Fact. Code Advance to next parameter. Alter Factory Code Set the factory settings access code to a value between and Return to top of page millisiemens/cm Return to Operating Page. 30 IM/4600-MEC Issue 0

33 462 and SIMPLE FAULT FINDING 9 SIMPLE FAULT FINDING 9. Error Messages If erroneous or unexpected results are obtained the fault may be indicated by an error message - see Table 9.. However, some faults may cause problems with instrument calibration or give discrepancies when compared with independent laboratory measurements. Error Message FAULTY PT000 FAULTY MODULE NV MEMORY ERROR CELL FOULING OVER/UNDER TEMP Possible Cause Temperature compensator/associated connections are either open/short circuit. The conductivity input module may be faulty. The contents of the non-volatile memory has not been read correctly during power up.* The conductivity cell has become contaminated and requires cleaning. The measured temperature is outside the limits specified for the selected range - see section 0, page 32. * To rectify the fault, switch off, wait 0 seconds and switch on again. If the fault persists contact the Company. Table 9. Error Messages 9.2 No Response to Conductivity Changes The majority of problems are associated with the conductivity cell, which must be cleaned as an initial check. It is also important that all program parameters have been set correctly and have not been altered inadvertently - see section 7, page 7. If the above checks do not resolve the fault:. Check that the instrument responds to a resistance input. Disconnect the conductivity cell cable and connect a 0 to 0kΩ decade resistance box directly to the instrument terminals as follows: Wall-mounted Instruments: a. Link terminals & 3, 4 & 7. b. Connect a 0Ω resistor between terminals 2 and 7. c. Connect a decade resistance box between terminals 3 & 4 to simulate the conductivity cell. Panel-mounted Instruments: a. Link terminals 6 & 9, 0 & 2. b. Connect a 0Ω resistor between terminals 6 and. c. Connect a decade resistance box between terminals 9& 0 to simulate the conductivity cell. Where: R = equivalent resistance G = conductivity in ms/cm. Failure to respond to the input indicates a faulty instrument. Return the instrument to the Company for repair. Correct response, but with incorrect readings, usually indicates an electrical calibration problem. Re-calibrate the instrument as detailed in Section If the response in step is correct, reconnect the conductivity cell cable and connect the resistance box to the cell end. Check that the instrument displays the correct values as set on the resistance box in this configuration. If the instrument passes check a) but fails check b), check the cable connections and condition. If the response for both checks is correct, replace the conductivity cell. 9.3 Checking the Temperature Input Check that the instrument responds to a temperature input. Disconnect the PT000 leads and connect a 0 to kω resistance box directly to the transmitter inputs - see Figs 4.4 or 4.5. Check that the instrument displays the correct values as set on the resistance box - see Table 9.2. Incorrect readings usually indicate an electrical calibration problem - re-calibrate the instrument as detailed in Section 8.3. Temperature ºC Input Resistance (Ω) Table 9.2 Temperature Readings for Resistance Inputs Select the Set Up Parameters Page and set the Temperature Compensation to 'NO' - see Temperature Compensation frame, see section 7.3, page 9. Check that the instrument displays the correct values as set on the resistance box, using the expression: R = 000 G IM/4600-MEC Issue 0 3

34 462 and SPECIFICATION 0 SPECIFICATION Display Measured value 5-digit x 7-segment backlit LCD Information 6-character, single line, dot matrix, backlit LCD Ranges Measured value Measuring range programmable 0 to 5mS/cm min. 0 to 400mS/cm at 50ºC (22ºF) max. 0 to 250mS/cm at 00ºC (22ºF) max. Scaling Conductivity ranges configurable as linear and bi-linear Temperature measuring range 0 to 00ºC (32º to 22ºF) Temperature compensation 0 to 00ºC (32º to 22ºF) Temperature coefficient 0.5 to 2.5%/ºC Temperature sensor Pt000 resistance thermometer Reference temperature 20 or 25ºC (68º or 77ºF) Accuracy ±.0% of FSD Linearity Better than % FSD Sodium Hydroxide (NaOH) range only Measuring ranges. 0 to 8% by wt. at 0 to 50ºC (32º to 22ºF) 2. 0 to 5% by wt. at 0 to 00ºC (32º to 22ºF) Accuracy ±0.% by wt. Linearity Better than 0.05% by wt. Sulfuric acid (H2SO4) and Hydrochloric acid (HCl) ranges only Measuring range 0 to 6% by wt. Temperature range 0 to 50ºC (32º to 22ºF) Accuracy ±0.% by wt. Linearity Better than 0.05% by wt. Environmental Data Operating temperature limits -20º to 55ºC (-4º to 3ºF) Storage temperature limits -25º to 55ºC (-3º to 3ºF) Operating humidity limits Up to 95% RH non-condensing Power Supply Voltage requirements 00 to 30V, 200 to 260V 50/60Hz Power consumption < 8VA AC Error due to power supply variation Less than 0.% for +6% -20% variation from nominal supply voltage Insulation Mains to earth (line to ground) 2kV RMS Outputs and Set Points No. of relays Two Relay contacts Single pole changeover Rating 250V AC 250V DC max. 3A AC Insulation 2kV RMS contacts to earth (ground) No. of set points Two (relay 2 programmable as cell-fouling alarm) Set points adjustment Programmable Set point hysteresis ±% of FSD (fixed) Local set point annunciation Red LED Remote range change facility 3A DC max. Loading (noninductive) 750VA 30W max. (inductive) 750VA 3W max. Available ranges 0-0mS/cm to 0-00mS/cm (SP5) 0-20mS/cm to 0-200mS/cm (SP9) 0-25mS/cm to 0-250mS/cm (SP28) 32 IM/4600-MEC Issue 0

35 462 and SPECIFICATION Mechanical Data Model 462 Wall-mount, Dimensions Weight protection IP66/NEMA4X 60mm wide x 24mm high x 68mm deep (6.30 in. x 8.43 in. x 2.68 in.) 2kg (4/2 lb) Model 4626 Panel-mount (/4 DIN), Dimensions Weight protection IP66/NEMA4X front 96mm wide x 96mm high x 9mm deep (3.78 in. x 3.78 in. x 7.52 in.).5kg (3/4 lb) Retransmission No. of retransmission signals One fully isolated, supplied as standard Second fully isolated output optional Output current 0 to 0mA, 0 to 20mA or 4 to 20mA programmable Output ranges Retransmission Zero 0, fixed Span 0 to 00% of the display range Retransmission 2 (optional) Programmable conductivity or temperature Conductivity as Retransmission Temperature0 to00ºc (32 to 22ºF), min. span 20ºC (36ºF) Accuracy ±0.25% FSD ±0.5% reading Resolution 0.% at 0mA, 0.05% at 20mA Max. load resistance 750Ω (20mA max.) SS/462 Issue 7 IM/4600-MEC Issue 0 33

36 462 and 4626 Appendix A Appendix A A. Automatic Temperature Compensation The conductivities of electrolytic solutions are influenced considerably by temperature variations. Thus, when significant temperature fluctuations occur, it is general practice to correct automatically the measured, prevailing conductivity to the value that would apply if the solution temperature was 25 C, the internationally accepted standard. Most commonplace, weak aqueous solutions have temperature coefficients of conductance of the order of 2% per C (i.e. the conductivities of the solutions increase progressively by 2% per C rise in temperature); at higher concentrations the coefficient tends to become less. The generally accepted expression relating conductivity and temperature is: Gt = G25 [ + (t - 25)] Where: Gt = conductivity at the temperature tºc G25 = conductivity at the standard temperature (25ºC) = temperature coefficient per ºC lies generally between.5%/ºc and 2.5%/ºC. When making temperature compensated measurements, a conductivity instrument must carry out the following computation to obtain G25: Gt G25 = [ + (t 25)] When the monitor is configured to measure a specific chemical compound i.e. %NaOH, then temperature compensation is automatic. A.. Calculation of Temperature Coefficient The temperature coefficient of a solution can be obtained experimentally by taking non-temperature compensated conductivity measurements at two temperatures and then applying the following expression: = Gt 2 Gt Gt [(t 2 25) Gt 2 (t 25)] Where: Gt2 = conductivity measurement at a temperature of t2 C Gt= conductivity measurement at a temperature of t C One of these measurements could be made at the ambient temperature and the other obtained by heating the sample. This method can only be applied when the instrument is being used on the conductivity range millisiemens/cm. Ensure that when applying this method the temperature compensation is set to 'NO' (refer to Temperature Compensation frame, Set Up Parameters Page) and the conductivity cell is allowed to stabilize before taking the conductivity readings, e.g. up to 0 minutes at one reading. A.2 4-Electrode Conductivity System Fig. A. A theoretical conductivity measurement system uses a 4-electrode cell comprising two outer 'current' electrodes, between which a current is passed through a sample solution, and two inner 'voltage' electrodes, which are used to measure the resultant voltage. The current supplied to the current electrodes is regulated electronically to maintain a constant voltage at the voltage electrodes. In common with all conductivity measuring systems, alternating current is used to prevent the affects of polarisation at the electrode surface. As the conductivity changes, the change in the resistance of the solution attempts to change the voltage between the voltage electrodes. However, a voltage amplifier is used to generate a control signal which controls the current generator. In turn this adjusts the current supplied to the current electrodes to reinstate the predetermined constant voltage between the voltage electrodes. The system is, in effect, a solid state servo system. The output signal, 'Vout', (see Table A.) is proportional to the conductivity of the solution and is derived across the 'Series Resistor' in the current supplied to the current electrodes. The resistance is inversely proportional to the conductivity of the sample. R G Electrode series resistances caused by electrode fouling. Vout Fig. A. 4-Electrode Conductivity System Solution Conductivity Electrodes Series Resistor Solution Resistance I I R2 Resistance R representing the Sample Solution. R4 Vin Voltage Controlled Current Generator R3 Voltage Amplifier Control Signal R Vin I Vout Low High Constant Low Low High Low Constant High High Table A. Output Signal 34 IM/4600-MEC Issue 0