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Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
Analytical Measurements:  Troubleshooting, Maintenance and the Future
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Analytical Measurements: Troubleshooting, Maintenance and the Future

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Focuses on measurement of pH, ORP (Redox), and Conductivity and aspects related to inline measurement of these critical analytical parameters. Discussion topics include scientific theory, measurement …

Focuses on measurement of pH, ORP (Redox), and Conductivity and aspects related to inline measurement of these critical analytical parameters. Discussion topics include scientific theory, measurement challenges, proper troubleshooting, installation, key applications, and the future of analytical measurements

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  • Some examples are: Beer 4,5 pH Milk 6,2 pH lemon juice 2,2 pH HCl 0,1 M 1 pH Activity a= concentration* activity factor. This activity factor is often estimated to be close to 1, and means activity~concentration
  • Describe reference system. Calomel reference (Hg/Hg 2 Cl 2 ) is the general electrochemical standard in place of the standard hydrogen electrode (describe!). Not suitable for industrial use: unstable above 60 o C toxic Preferred system is Ag/AgCl, essentially as good as the Calomel system but high temperature stable.
  • Walther Nernst developed the equation that bears his name in 1880’s (published 1889) Eo ‘standard’ potential for the electrode R universal gas constant T temperature (absolute, degrees Kelvin) F Faraday constant Valence number of ion not shown since it is 1
  • Walther Nernst developed the equation that bears his name in 1880’s (published 1889) Eo ‘standard’ potential for the electrode R universal gas constant T temperature (absolute, degrees Kelvin) F Faraday constant Valence number of ion not shown since it is 1
  • Walther Nernst developed the equation that bears his name in 1880’s (published 1889) Eo ‘standard’ potential for the electrode R universal gas constant T temperature (absolute, degrees Kelvin) F Faraday constant Valence number of ion not shown since it is 1
  • Some solutions aggressive towards the sensor and cause loss of calibration quicker than others pH 7 + 2.5 needs less calibration than pH 5.2 + 0.2 Quality - who makes it!
  • Walther Nernst developed the equation that bears his name in 1880’s (published 1889) Eo ‘standard’ potential for the electrode R universal gas constant T temperature (absolute, degrees Kelvin) F Faraday constant Valence number of ion not shown since it is 1
  • Walther Nernst developed the equation that bears his name in 1880’s (published 1889) Eo ‘standard’ potential for the electrode R universal gas constant T temperature (absolute, degrees Kelvin) F Faraday constant Valence number of ion not shown since it is 1
  • Walther Nernst developed the equation that bears his name in 1880’s (published 1889) Eo ‘standard’ potential for the electrode R universal gas constant T temperature (absolute, degrees Kelvin) F Faraday constant Valence number of ion not shown since it is 1
  • Conductivity is affected by temperature since water becomes less viscous at higher temperatures and ions can move more easily—they have greater mobility. Typical mineral ions increase in conductivity by about 2% of value per °C. Temperature as well as water purity can change the conductivity. For this reason, it has become an industry standard to compensate measurements to 25°C. That is, the conductivity value is reported as if the sample were at 25°C. General purpose temperature compensation provides the typical 2% per °C correction.
  • Conductivity is affected by temperature since water becomes less viscous at higher temperatures and ions can move more easily—they have greater mobility. Typical mineral ions increase in conductivity by about 2% of value per °C. Temperature as well as water purity can change the conductivity. For this reason, it has become an industry standard to compensate measurements to 25°C. That is, the conductivity value is reported as if the sample were at 25°C. General purpose temperature compensation provides the typical 2% per °C correction.
  • To minimize the problems of the two electrode design, a different method has been developed.
  • Four-electrode measurement refers to a conductivity sensor incorporating four electrodes into its probe body instead of the usual two. The four-electrode measuring technique is used for highly conductive and/or dirty water samples which would foul the surfaces and/or plug the narrow passages of conventional two-electrode conductivity sensors. Suspended solids, turbidity, silt and oils tend to coat electrode surfaces and accumulate in passages and produce negative conductivity errors with two-electrode conductivity systems. Four-electrode measurement applies an AC current through the sample via two outer drive electrodes. These electrodes may become fouled and the circuit will compensate to maintain the AC current level. Two inner measuring electrodes are used to sense the voltage drop through the portion of solution between them. The circuit makes a high impedance AC voltage measurement, drawing negligible current and making it much less affected by additional resistance due to fouling of the measuring electrode surfaces.
  • 1. Electrode surface condition for high conductivity measurements with two-electrode systems is critical. The surface must be rough on a microscopic scale in order to provide very intimate contact with the sample. Otherwise a high resistance at the interface would cause low conductivity readings. 2. Coatings which insulate the electrodes of a two-electrode sensor have a direct impact on the accuracy, especially when the conductivity of the sample is high. Moderate insulation of the electrodes of four-electrode sensors has no effect since the voltage measurement is made with virtually no current flow. 3. The flat surface of four-electrode sensors is largely self-cleaning in high flow applications.
  • Inductive conductivity provides the best tolerance for fouling conditions, with no electrodes in contact with the sample. It can also be used for high purity chemical concentration measurements with its excellent chemical resistance and no wetted metal parts. Insertion and submersion mounting are available.
  • Conductivity cell installation must assure that the cell is completely immersed in water. No bubbles can be within the annular space between electrodes or erroneously low conductivity (high resistivity) readings will result. Upward flow is desirable so air can easily escape.
  • When installing in large pipe, do not use a series of reducing bushings that would create a “dead leg” of stagnant water around the cell. Tap directly into the pipe or into a pipe plug in a Tee. Deionization resin beads, if they escape from a column, can become lodged between the electrodes of a conductivity cell and short them, causing erroneously high conductivity (low resistivity) readings.
  • When installing in large pipe, do not use a series of reducing bushings that would create a “dead leg” of stagnant water around the cell. Tap directly into the pipe or into a pipe plug in a Tee. Deionization resin beads, if they escape from a column, can become lodged between the electrodes of a conductivity cell and short them, causing erroneously high conductivity (low resistivity) readings.
  • When installing in large pipe, do not use a series of reducing bushings that would create a “dead leg” of stagnant water around the cell. Tap directly into the pipe or into a pipe plug in a Tee. Deionization resin beads, if they escape from a column, can become lodged between the electrodes of a conductivity cell and short them, causing erroneously high conductivity (low resistivity) readings.
  • Typical ranges of applications are shown in resistivity, conductivity and Total dissolved solids (ppm TDS) units. The TDS scale here is based on the concentration of sodium chloride that would have the identified conductivity and resistivity. Other substances such as calcium carbonate may be use as the basis.
  • As we all know, In the sensor a small microprocessor has been integrated, that stores and process all relevant data. All this information is then digitally transferred to the instrument without any risk of interferences. The microprocessor is also able to store information like calibration values, identity and timestamp the maximum process temperature. What is even more interesting with ISM is the connection possibilities and how the sensors can perform there own diagnostics in real-time.
  • With the ISM we have transferred the technology experience and know how that we have collected over the years into the sensor and the sensor head. In the sensor a small microprocessor has been integrated, that stores and process all relevant data. All this information is then digitally transferred to the instrument. With this new technology, the ISM sensors are able to perform its own diagnostics in real-time. All our new transmitters are ready to handle the ISM technology and together with the ISM sensors they can perform true predictive maintenance.
  • SLIDE CAN BE SKIPPED IN CASE OF TIME PRESSURE There is an overlap in measuring range for inductive and 4E cond. Sensors We position the 4E sensors mainly for chemical, pharma-, and F&B application where the conditions are not to harsh. The inductive sensors are designed for chemical and P&P industrie where you have harsh conditions. Nevertheless, if the customer insist on either a 4E or inductive solution we now can offer both sensor types with best performance. SLIDE CAN BE SKIPPED IN CASE OF TIME PRESSURE
  • Transcript

    • 1. pH & Conductivity Parameter Training Measurement, Maintenance & the Future ISA Boston Section March 15, 2011 U E 2 E 3 E 1 Reference- electrolyte E 6 E 5 E 4 Inner Buffer
    • 2. What is pH ? <ul><li>The statements: “ Acid ” “ Neutral ” “ Alkaline ” </li></ul><ul><li>are replaced with precise numerical values </li></ul>
    • 3. Definition: pH = - log [a H+ ] H 2 0 H + + OH - [ a H+ ] * [ a OH- ] / [a H2O ] = 10 -14 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH acidic: pH 0-6.9 [H + ] > [OH - ] [H + ] > 10 -7 M neutral: pH 7.0 [H + ] = [OH - ] [H + ]= 10 -7 M alkaline: pH 7.1 - 14 [H + ] < [OH - ] [H + ] < 10 -7 M pH basics - pH scale
    • 4. Some examples of pH values 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 lemon juice orange juice beer cheese milk pure water egg white borax Milk of Magnesia H 2 SO 4 (1N) 4.9% HCl (0.1N) 0.37% acetic acid (0.1N) 0.6% HCN (0.1N) 0.27% sodium bicarbonate 0.84% (0.1N) potassium ac. 0.98% (0.1N) NH 4 OH 0.017% (0.01N) NH 4 OH 1.7% 1.0N NaOH 4%
    • 5. How does pH measurement work? pH is a potentiometric measurement via an electrochemical sensor/electrode/probe U= E pH -E ref (mV) This potential difference is a function of the solution being measured E pH glass electrode E ref reference electrode high impedance pH Meter
    • 6. Combination pH Sensors
    • 7. What is special about pH glass? H + H + + + + + + + - - - - - - Acidic Alkaline Glass membrane Glass membrane (0.2 - 0.5mm) Gel layer ca. 1 µm (outer and inner) positive charge negative charge internal buffer The surface layer of the glass membrane is the “key performer” in each pH measurement! pH is a measurement of the potential difference between inner and outer layer of glass membrane! This is one reason why pH sensors need to be stored in salt solution when not in use!
    • 8. <ul><li>E 1 Potential of the reference lead-off system </li></ul><ul><li>E 2 Diaphragm or diffusion potential </li></ul><ul><li>E 3 Potential of internal lead-off </li></ul><ul><li>E 4 Potential on the inner surface </li></ul><ul><li>E 5 pH dependent potential (on the outside of the membrane) </li></ul>What is a combination electrode? pH meter Reference electrolyte Inner buffer Potential of the glass electrode (E 5 ) can’t be measured individually. A second (reference) electrode is necessary. The potential of this electrode must be independent of the sample solution (buffer) Combined pH electrode- glass and reference electrode integrated E 1 E 2 E 3 E 4 E 5
    • 9. Reference Junction Biotech pH sensors have a reference junction typically composed of ceramic <ul><li>Ceramic has uniform pore size and allows for capillary action to connect the reference buffer to the process </li></ul><ul><li>Many Mettler-Toledo sensors have pressurized reference systems that physically push buffer out of the sensor </li></ul>
    • 10. The Nernst Equation E = E 0 + 2.303 R T log n F 1. Internal Reference Potential 2. Inner Glass/Solution Potential 3. External Reference Potential 4. LIQUID JUNCTION POTENTIAL
    • 11. The Nernst Equation E = E 0 + 2.303 R T log n F 2.303 R T is known as “The Electrode Slope” n F IDEAL SLOPE = 59.16 mV/pH unit at 25 °C Slope is temperature dependent
    • 12. The Nernst Response Curve  mV = 59.16   pH mV E = E o + 2.3 RT/F log a H + where 2.3 RT/F = 0.198T K = 59.16 mV @ 25 o C
    • 13. pH Electrode Calibration Curve pH 0 4 7 10 14 + 500 mv 0 mv - 500 mv millivolts pH 10.00 buffer 0.0 millivolts pH 7.00 buffer -177.5 millivolts IDEAL VALUES!
    • 14. Understanding Temperature Compensation <ul><li>There are two temperature effects to account for: </li></ul><ul><ul><li>Nerstian (graph on the left dealing with the physical nature of the sensor) </li></ul></ul><ul><ul><ul><li>This is what temperature compensation handles </li></ul></ul></ul><ul><ul><li>Solution temperature dependence </li></ul></ul><ul><ul><ul><li>This is an actual temperature effect that you want to measure. </li></ul></ul></ul>0 o C 25 o C 30 o C 20 o C 40 o C 10 o C  +/- 0.6 pH Isopotential point
    • 15. Temperature Error (No Temp. Compensation) Temperature error table for pH signal pH °C 2 3 4 5 6 7 8 9 10 11 12 5 0.30 0.24 0.18 0.12 0.06 0 0.06 0.12 0.18 0.24 0.30 15 0.15 0.12 0.09 0.06 0.03 0 0.03 0.06 0.09 0.12 0.15 25 0 0 0 0 0 0 0 0 0 0 0 35 0.15 0.12 0.09 0.06 0.03 0 0.03 0.06 0.09 0.12 0.15 45 0.30 0.24 0.18 0.12 0.06 0 0.06 0.12 0.18 0.24 0.30 55 0.45 0.36 0.27 0.18 0.09 0 0.09 0.18 0.27 0.36 0.45 65 0.60 0.48 0.36 0.24 0.12 0 0.12 0.24 0.35 0.48 0.60 75 0.75 0.60 0.45 0.30 0.15 0 0.15 0.30 0.45 0.60 0.75 85 0.90 0.72 0.54 0.36 0.18 0 0.18 0.36 0.54 0.72 0.90 No temperature error Temperature error < 0.1 pH units Temperature error > 0.1 but < 0.3 pH units Temperature error = or > 0.3 pH units ( simplified model with Error = /pH (pr.) - 7/ x /(T (pr.) - 25):10/ x 0.03 )
    • 16. Causes of Failure or Measurement issues <ul><li>Bubbles forming at the tip on the inside of the sensor </li></ul><ul><ul><li>Mount sensor 15 degrees to vertical </li></ul></ul><ul><li>Reference Junction Fouling due to coating or chemical reaction. </li></ul><ul><ul><li>Keep the reference clean </li></ul></ul><ul><li>Reference Poisoning due to ingress and chemical reaction. </li></ul><ul><li>Pre-mature aging due to exposure to heat. </li></ul><ul><ul><li>Such as SIP or steam sterilization </li></ul></ul>
    • 17. <ul><li>Coating of the glass or even binding of critical ions. </li></ul><ul><li>Abrasion of the glass. </li></ul><ul><li>Electrical Connection failure due to moisture intrusion, incomplete connection, dirty or corroded contacts, etc. </li></ul><ul><li>Calibration issues </li></ul>Causes of Failure or Measurement issues
    • 18. pH Calibration 101- Bracket your process pH pH 0 4 7 10 14 + 500 mv 0 mv - 500 mv millivolts pH 10.00 buffer 0.0 millivolts pH 7.00 buffer -177.5 millivolts Process pH value <ul><li>Cardinal Rules for pH Calibration </li></ul><ul><li>Always have your calibration buffers “bracket” your process pH measurement of interest. </li></ul><ul><ul><li>Example; Process pH of 8.2 should utilize 7 and 10 buffers </li></ul></ul><ul><li>Never calibrate with two buffers more than 3 pH units apart. </li></ul>
    • 19. pH Calibration-Impact of buffers <ul><li>Importance of good buffers </li></ul><ul><ul><li>Buffer quality is variable </li></ul></ul><ul><ul><ul><li>Does 7 buffer contain a biostat? </li></ul></ul></ul><ul><ul><ul><li>Is accuracy +/-0.01 or 2 </li></ul></ul></ul><ul><ul><ul><li>Is there a pH v. temperature table? </li></ul></ul></ul><ul><ul><li>Buffers are nominal values </li></ul></ul><ul><ul><ul><li>Choose the right automatic table or a custom. </li></ul></ul></ul><ul><ul><li>Alkaline buffers >10 readily absorb CO 2 and change pH. </li></ul></ul><ul><ul><li>Mind contamination and aging aspects. </li></ul></ul><ul><li>Automatic temperature compensation and buffer tables automatically select the proper buffer value at a given temperature increasing calibration accuracy. </li></ul>
    • 20. pH Calibration /Justification 1. Step Determine Asymmetry Potential / Zero Point 2. Step Determine the Slope pH Buffer 7.00 pH Buffer 4.00 [mV] 200 -200 pH 7 14 [mV] 200 -200 pH 7 14 pH as 4 [%] Slope
    • 21. pH Calibration <ul><li>Always ensure the electrode is clean before calibration. </li></ul><ul><li>Zero point: pH 7 buffer. The E0 point is a critical point in the calibration curve and an indication of sensor status. Should be close to 0 mV </li></ul><ul><li>Use fresh buffers. </li></ul><ul><li>Bracket your process measurement when calibrating </li></ul><ul><li>Rinse the electrode and dab dry between calibration measurements. Do not rub the electrode. Rubbing could cause static charges and disrupt sensor function. </li></ul><ul><li>Make sure you have an acceptable slope and fast response time. Good transmitters will tell you how your sensor is doing. </li></ul><ul><li>-Good slopes range from 90% to 101% (possibly even lower) </li></ul><ul><li>-A pH sensor should reach a stable value in buffer in 30S or less </li></ul>
    • 22. pH Simulator (mV input) <ul><li>Simulates an ideal electrode in different buffers and at different temperatures, also accounting for the resistance of the pH-glass membrane. Using the simulator it is possible to check the amplifier for: </li></ul><ul><li>Calibration and linearity </li></ul><ul><li>pH cable viability </li></ul><ul><li>Temperature compensation </li></ul><ul><li>Quality of input circuitry (resistance and current) </li></ul><ul><li>Presence of ground loops </li></ul>
    • 23. How frequently should the sensor be calibrated? <ul><li>Depends on a few factors: </li></ul><ul><li>The nature of the solution being measured </li></ul><ul><li>The accuracy required by your SOP </li></ul><ul><li>The quality of the sensor </li></ul>
    • 24. Grab Samples- Why don’t they agree? <ul><li>Physical changes to the grab sample </li></ul><ul><li>Sample pH not stable </li></ul><ul><li>Sample reacted with CO 2 or other atmospheric gas </li></ul><ul><li>Sample temperature different from process </li></ul><ul><li>Sample hot, electrode cool </li></ul>37 o C 20 o C Same sample
    • 25. pH Sensor Installation (How to Install) <ul><li>All of our pH sensors use liquid buffer in the sensing electrode OR liquid electrolyte in the reference. Therefore proper installation of a pH sensor is 15 degrees above horizontal! </li></ul>15 °
    • 26. pH Sensor Installation (How NOT to Install) <ul><li>Sensors mounted horizontally / parallel to the ground or worse UPSIDE DOWN tend to form an air bubble between the glass and internal electrolyte of the sensor </li></ul>Air Bubble NO! HECK NO!
    • 27. pH Recap <ul><li>Take care of the glass tip and reference junction! </li></ul><ul><li>Shake down the pH sensor </li></ul><ul><li>Remove the silicone bead from the reference junction </li></ul><ul><li>Keep the sensor hydrated in 3 molar KCl or even 4 buffer </li></ul><ul><li>Remember: These sensors have a shelf life </li></ul><ul><li>Install the sensor 15 degrees to vertical </li></ul><ul><li>Bracket your process pH measurement when calibrating with buffers </li></ul><ul><li>Be wary of buffer shelf life and alkaline buffers absorbing CO 2 </li></ul><ul><li>Make sure temperature isn’t a factor </li></ul><ul><li>Buffer 7 should be darn near 0 millivolts </li></ul><ul><li>Each pH measurement unit shift should account for 59.16mV </li></ul><ul><li>Use a pH simulator if you suspect a problem with the cable or transmitter </li></ul>
    • 28. What is ORP ? <ul><li>The qualitative statements, such as </li></ul><ul><li>“ Oxidizing ” “ Reducing ” </li></ul><ul><li>are replaced with Redox (ORP) potential values </li></ul><ul><li>You may also hear the term “Redox” </li></ul>
    • 29. What is REDOX measurement tell you? <ul><li>The REDOX potential is a measurement of the affinity of a solution to either gain or lose electrons when it is subject to change by introduction of a new species. </li></ul><ul><li>-A solution with a higher (more positive) reduction potential than the new species will have a tendency to gain electrons from the new species (i.e. to be reduced by oxidizing the new species). </li></ul><ul><li>-A solution with a lower (more negative) reduction potential will have a tendency to lose electrons to the new species (i.e. to be oxidized by reducing the new species). </li></ul>
    • 30. ORP (Oxidation Reduction Potential) <ul><li>Also known as “redox” </li></ul><ul><li>Oxidation— reaction w/ loss of electrons, higher potential </li></ul><ul><li>Reduction—reaction w/ gain of electrons, reduced potential </li></ul><ul><li>Measurement is again a combination electrode but this time it is the reference system of a pH sensor and platinum indicator electrode. </li></ul><ul><li>Still have to keep the reference diaphragm happy but platinum is more resilient than glass </li></ul>
    • 31. ORP (Oxidation Reduction Potential) <ul><li>Potential is generated by the relative concentration of chemical oxidants and reductants </li></ul><ul><li>Oxidation can happen even in the absence of oxygen </li></ul><ul><ul><li>Mg + Cl 2 -> Mg2+ + 2Cl- </li></ul></ul><ul><ul><li>In this reaction Mg is oxidized because it loses electrons and Cl is reduced because it gains electrons </li></ul></ul><ul><li>Since the sensor is non-selective for Oxidants or reductants, the presence of either will contribute to the overall ORP value. </li></ul>E = E 0 + kT log [Oxidants][H + ] [Reductants]
    • 32. pH effect on ORP <ul><li>Potential (E) increases as [H + ] increases (pH decreases) </li></ul><ul><li>Potential (E) decreases as [H + ] decreases (pH increases) </li></ul>E = E 0 + kT log [Oxidants] [H + ] [Reductants]
    • 33. Temperature effect on ORP <ul><li>Potential (E) increases as temperature (T) increases </li></ul><ul><li>Potential (E) decreases as temperature (T) decreases </li></ul>E = E 0 + k T log [Oxidants][H + ] [Reductants]
    • 34. Questions?
    • 35. What is Conductivity? <ul><li>Measures only ionic (conductive) species </li></ul><ul><li>Fundamental measure of water purity </li></ul><ul><li>Mineral content </li></ul><ul><li>Chemical concentration </li></ul>Conductivity is the ability of a solution to carry an electric current.
    • 36. Conductivity Measurement A conductivity “cell”, sensor, or electrode is an “electro-mechanical” measurement 1 cm 1 cm d = 1 cm Cond Solution Electrode plate VAC
    • 37. Conductivity Advantages and Limitations <ul><li>ADVANTAGES </li></ul><ul><ul><li>Simple </li></ul></ul><ul><ul><li>Fast responding </li></ul></ul><ul><ul><li>Low cost </li></ul></ul><ul><ul><li>Reliable </li></ul></ul><ul><li>LIMITATIONS </li></ul><ul><ul><li>Non-specific </li></ul></ul><ul><ul><li>Limited sensitivity </li></ul></ul>
    • 38. Electrolytes <ul><li>Acids </li></ul><ul><ul><li>Substances which ionize in solution and produce hydrogen ions, H + </li></ul></ul><ul><ul><li>Hydrochloric Acid (HCl) dissociates into H + + Cl - </li></ul></ul><ul><li>Bases </li></ul><ul><ul><li>Substances which ionize in solution and produce hydroxide ions, OH - </li></ul></ul><ul><ul><li>Sodium Hydroxide, NaOH, dissociates into Na + + OH - </li></ul></ul><ul><li>Salts </li></ul><ul><ul><li>Substances which ionize in solution and produce neither hydrogen or hydroxide ions </li></ul></ul><ul><ul><li>Sodium Chloride, NaCl, dissociates into Na + + Cl - </li></ul></ul>
    • 39. Conductivity- An Electro-mechanical Measurement <ul><li>Conductivity Calculation: </li></ul><ul><li>Conductance (meter) x Cell Constant (sensor) = Conductivity </li></ul><ul><li>14.13 mS x 0.1 /cm = 1413 µ S/cm </li></ul>Known Known Back Calculate
    • 40. Conductance and Resistance <ul><li>Conductance is the reciprocal of resistance </li></ul><ul><li>Conductance = 1/Resistance </li></ul><ul><li>1 µS = 1 Meg ohm </li></ul><ul><li>0.055 µS = 18.3 Meg ohm </li></ul><ul><li>Units of resistance are in Ohms (  ) </li></ul><ul><li>Units of conductance are measured in Siemens </li></ul><ul><li>1,000 µS (micro-Siemens) = 1 mS (milli-Siemens) </li></ul><ul><li>1,000 mS (milli-Siemens) = 1 S (Siemen) </li></ul><ul><li>1,000,000 µS (micro-Siemens) = 1 S (Siemen) </li></ul><ul><li>[Don’t confuse micro and milli !] </li></ul>
    • 41. Conductivity Units of Measure <ul><li>Resistance ohm </li></ul><ul><li>Resistivity ohm-cm </li></ul><ul><li>Conductance siemens = 1 / ohm </li></ul><ul><li>Conductivity siemens/cm </li></ul><ul><ul><ul><ul><ul><li>microsiemens/cm (µS/cm) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li> millisiemens/cm (mS/cm) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>microsiemens/ m (µS/ m ) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li> millisiemens/ m (mS/ m ) </li></ul></ul></ul></ul></ul><ul><li>Total Dissolved Solids (ppm TDS) </li></ul>
    • 42. Conductivity vs. Concentration <ul><li>Conductivity is non-specific; it responds to the sum of all ions in solution </li></ul><ul><li>Can be used for concentration: </li></ul><ul><li>In binary systems (1 chemical in water) </li></ul><ul><li>Other chemicals contribute little conductivity compared to chemical of interest </li></ul><ul><li>Background of other chemicals remains relatively constant </li></ul>
    • 43. Chemical Concentration Control
    • 44. Chemical Concentration Control
    • 45. Cell Geometry The measured resistance will be dependent on the spacing of the electrode – cell geometry  “cell constant” Therefore, units measurement has dimension component, ex. mS/cm 1 cm 1 cm d = 1 cm Cond Solution Electrode plate VAC
    • 46. Measuring Conductivity ~ H H O Na + Cl - H + O H -
    • 47. Typical Conductivity Values <ul><li>Surface water ~ 250 µS/cm </li></ul><ul><li>Well water ~600 µS/cm </li></ul><ul><li>RO Water ~5 µS/cm </li></ul><ul><li>USP Water ~1 µS/cm </li></ul><ul><li>UPW 18 meg ohm </li></ul><ul><li>CIP Solution~60 mS/cm </li></ul>
    • 48. Common Measurement Challenges <ul><li>Temperature Compensation </li></ul><ul><li>Calibration </li></ul><ul><li>Coating </li></ul>
    • 49. Concentration <ul><li>As concentration increases, conductivity generally increases. </li></ul>
    • 50. Conductivity Temperature Effects ~ H + H H O O H - Na + Cl - H + O H - Na + Cl -
    • 51. Temperature Coefficients <ul><li>Temperature effects vary by ion type. Some typical temperature coefficients: </li></ul>Sample %/ o C (at 25 o C) Salt solution (NaCl) 2.12 5% NaOH 1.72 Dilute Ammonia Solution 1.88 10% HCl 1.32 5% Sulfuric Acid 0.96 98% Sulfuric Acid 2.84 Sugar Syrup 5.64
    • 52. Sensor Cell Constant 0.1 cm 0.1 cm -1 0.1 cm 1 cm Conductivity Cell Constant = Length Area 1 cm 1 cm 2 = = 1 cm -1 INSULATOR ELECTRODE ELECTRODE INNER OUTER 1 cm 1 cm
    • 53. Contacting Conductivity <ul><li>Two-Electrodes (Concentric Design) </li></ul><ul><ul><li>Conductivity < 10 mS/cm </li></ul></ul><ul><ul><li>Polarization errors - high conductivity </li></ul></ul><ul><ul><li>Electrode coating errors significant </li></ul></ul>
    • 54. Conductivity Traceable Calibration <ul><li>Accuracy of cell constant </li></ul><ul><li>Accuracy of temperature measurement </li></ul>
    • 55. Conductivity Instrument Calibration <ul><li>NIST Traceable Resistances to cover ranges of measurement for conductivity and temperature </li></ul><ul><ul><li>Decade Boxes </li></ul></ul><ul><ul><li>Instrument-specific Calibrators </li></ul></ul>
    • 56. Contacting Conductivity <ul><li>Four-Electrode Cell </li></ul><ul><ul><li>AC voltage applied to outer electrodes, voltage induced upon inner electrodes </li></ul></ul><ul><ul><li>Measure induced voltage </li></ul></ul><ul><ul><li>Minimizes polarization and electrode coating effects </li></ul></ul><ul><ul><li>Conductivity: 0.02 to 800 mS/cm </li></ul></ul>V
    • 57. Four-Electrode Conductivity Measurement AC Current Source AC Voltage Measurement Drive Electrodes Measuring Electrodes Four Electrode Sensor Four-Electrode Measuring Instrument
    • 58. Four-Electrode Conductivity Measurement <ul><li>Four-electrode sensors and instruments can tolerate poor measuring conditions because: </li></ul><ul><ul><li>Electrode metal surface condition is less important. </li></ul></ul><ul><ul><li>Electrode fouling or coating has less effect. </li></ul></ul><ul><ul><li>Four-electrode sensors do not have the narrow channels of high, two-electrode cell constants. The resulting flat surface design is much less vulnerable to fouling. </li></ul></ul>
    • 59. Inductive Conductivity <ul><li>“ Electrode less ” </li></ul><ul><ul><li>Sending coil induces a conductivity dependent current in receiving coil </li></ul></ul><ul><ul><li>High conductivity solutions </li></ul></ul><ul><ul><li>Electrode coating effects eliminated </li></ul></ul><ul><ul><li>Conductivity: 0.05 to 2000 mS/cm </li></ul></ul>Energized Measured G D induced current
    • 60. Inductive Conductivity Measurement <ul><li>Virtually non-fouling so it is great for sludge, oils, high particulate matter </li></ul><ul><li>No metal/solution contact </li></ul><ul><li>Reliable high conductivity measurements </li></ul><ul><li>Relatively large sensor size </li></ul><ul><li>Cell constant can be affected by surrounding pipe </li></ul>
    • 61. Inductive Sensor Installation <ul><li>What distance from a wall should be kept when installing an inductive sensor in the pipe? </li></ul>metal synthetic Measuring value too low Measuring value too high Measuring value correct 30mm / 1.18” 30mm / 1.18”
    • 62. Cell Installation -2 electrode <ul><li>Conductivity cell installation must assure that the cell is completely immersed in water. </li></ul><ul><li>No bubbles can be within the annular space between electrodes or erroneously low conductivity (high resistivity) readings will result. </li></ul><ul><li>Upward flow is desirable so air can easily escape. </li></ul>Recommended Cell Installation... Flow should be directed at the end of the sensor
    • 63. Cell Installation -2 electrode NOT Recommended Cell Installation... INLET OUTLET OUTLET AIR INLET Avoid dead legs and air traps
    • 64. Cell Installation -4 electrode Recommended OUTLET INLET Maintain a minimum clearance between sensor and pipe
    • 65. Cell Installation -4 electrode NOT Recommended Maintain a minimum clearance between sensor and pipe
    • 66. Conductivity, Resistivity, TDS Ranges Conductivity 100M 10M 1M 100K 10K 1K 100 10 1 Ultrapure water Deionized water Distilled water Condensate Drinking water Cooling tower water Percentage of acids, bases and salt Waste water Brackish water, Sea water Water for Industrial Process 5% Salinity 2% NaOH 20% HCl 0.01 .1 1 10 100 1000 10k 100k 1000k 0.021 0.4 4.6 46 460 4.6k 46k TDS ppm Conductivity and resistivity are measured at 25  C; TDS is expressed as Sodium Chloride (NaCl) Resistivity ohm-cm µS-cm
    • 67. Main Applications and Measuring Range Inductive 4 Elec 2 Elec 0.01 0.1 1.0 10 100 1000 10k 100k 1000k Conductivity ( µ S/cm) 100 M 10M 1M 100k 10k 1000 100 10 1 Resistivity (Ohm-cm) Ultra pure water Pure water Make up water Drinking water Diluted acids, bases, salts Waste water Brackish water Industrial process water Acids, bases Water Processes Biotech/Food and Beverage Chemical Processes
    • 68. So….where is analytical measurement today?
    • 69. Previous Analog Technology Digital technology provides better sound quality
    • 70. Welcome to the Digital World! Same electrochemical end of the sensor converted to digital signal which is more robust and gives more information
    • 71. Analog Sensor Technology Most analog sensors provide the user with one piece of information to determine the health of the sensor: Slope Limited information for troubleshooting
    • 72. ISM: The Evolution of the Sensor The processing of sensor diagnostics is fully integrated in the sensor electronics <ul><li>Sensors can be pre-calibrated for easy and effective maintenance </li></ul><ul><li>More connectivity options </li></ul><ul><ul><li>Transmitter </li></ul></ul><ul><ul><li>PC with iSense Suite </li></ul></ul><ul><ul><li>Cableless module </li></ul></ul><ul><li>Diagnostics data always updated by the sensor </li></ul><ul><ul><li>DLI: Dynamic Lifetime Indicator </li></ul></ul><ul><ul><li>ACT: Adaptive Calibration Timer </li></ul></ul><ul><ul><li>TTM: Time to Maintenance </li></ul></ul>All information is processed in the sensor for connectivity flexibility
    • 73. How Does Digital Sensor Technology Work? <ul><li>With the ISM digital technology we have transferred the technical sensor experience and know how that we have collected over the years into the sensor and the sensor head. </li></ul><ul><li>A small microprocessor in the sensor head stores and processes all relevant data. </li></ul><ul><li>This information is digitally transferred to the instrument. </li></ul><ul><li>ISM sensors are able to perform their own diagnostics in real-time and in conjunction with our transmitters they can achieve predictive maintenance </li></ul>
    • 74. iSense™ ISM Asset Suite <ul><li>Intuitive interface </li></ul><ul><li>No transmitter as interface required </li></ul><ul><li>Key performance indicators for fast sensor diagnosis </li></ul><ul><li>Sensor status is visualized </li></ul>iSense allows verification and calibration of pH and DO sensors in lab conditions iSense is key to maximize the benefits of the ISM technology
    • 75. UniCond ® Conductivity Sensors with ISM ® <ul><li>Conductivity measuring circuit built into sensor body </li></ul><ul><ul><li>UniCond eliminates cable resistance and capacitance effects </li></ul></ul><ul><ul><ul><li>Traditional systems may have to transmit the analog AC conductivity signal through cable 50 meters long. </li></ul></ul></ul><ul><ul><ul><li>With UniCon, the analog signal goes only 50 mm ! </li></ul></ul></ul><ul><ul><ul><li>It eliminates analog signal interference. </li></ul></ul></ul><ul><ul><li>THORNTON’s unique conductivity measurement method optimizes sensor accuracy. </li></ul></ul><ul><ul><ul><li>With no signal degradation along the cable, UniCond delivers higher accuracy over greater distances. </li></ul></ul></ul><ul><ul><ul><li>Measurement range is greatly expanded without loss of accuracy . </li></ul></ul></ul>UniCond ® sensors provide breakthrough performance! 50 mm 50 meters
    • 76. UniCond ® Conductivity Sensors with ISM ® <ul><li>UniCond delivers enhanced system accuracy that out-performs analog conductivity sensors </li></ul><ul><ul><li>Analog conductivity systems calibrate sensor and measuring circuit separately, with contributions to error from both, e.g. </li></ul></ul><ul><ul><ul><li>Sensor cell constant accuracy: ± 1% </li></ul></ul></ul><ul><ul><ul><li>Transmitter accuracy: ± 0.5% </li></ul></ul></ul><ul><ul><ul><li>System accuracy, ± 1.5% plus cable effects </li></ul></ul></ul><ul><ul><li>UniCond System accuracy </li></ul></ul><ul><ul><ul><li>No error contributed by transmitter </li></ul></ul></ul><ul><ul><ul><li>No error contributed by cable or noise pickup </li></ul></ul></ul><ul><ul><ul><li>System accuracy = cell constant accuracy = ± 1%, a 33% improvement in accuracy </li></ul></ul></ul>UniCond ® provides accuracy at least 33% better than analog conductivity sensors!
    • 77. Applications and Measurement Range Expanded range with enhanced accuracy! 0.01 0.1 1.0 10 100 1000 10k 100k 1000k Conductivity ( µ S/cm) 100 M 10M 1M 100k 10k 1000 100 10 1 Resistivity (Ohm-cm) Ultra pure water Pure water Make up water Drinking water Diluted acids, bases, salts Waste water Brackish water Industrial process water Acids, bases CURRENT 4E RANGE CURRENT 2E RANGE UniCond ® extends the range of measurement to cover UPW to seawater with a single sensor! UPW to seawater with a single UniCond ® sensor !
    • 78. <ul><li>Thank you! </li></ul>
    • 79. Questions?

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