Conductivity Theory

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Conductivity Theory

• Applied to Proper Hardware Selection

2
Conductivity Measurement

• Used to Measure and Control the Percent
  Concentration of Acids, Bases and Salts in
  Solution
• Measures Total Concentration
• Not Ion Specific
• May be Used to Determine the Dominant Chemical

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Electrolytes

• Acids
• Substances which ionize in solution and produce
  hydrogen ions, H
• Hydrochloric Acid (HCl) dissociates into H Cl-
• Bases
• Substances which ionize in solution and produce
  hydroxide ions, OH-
• Sodium Hydroxide, NaOH, dissociates into Na
  OH-
• Salts
• Substances which ionize in solution and produce
  neither hydrogen or hydroxide ions
• Sodium Chloride, NaCl, dissociates into Na Cl-

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Typical Conductivity Values
5
Conductivity Measurement

• Units of Measurement
• U.S. Units Micromhos/cm
• International Units MicroSiemens/cm
• 1.0 S/cm 1,000 mS/cm 1,000,000 uS/cm
• umho/cm uS/cm
• Conductivity is the Reciprocal of Resistance
• 1.0 MicroSiemen/cm 1,000,000 Ohms/-cm
• 1,000,000 MicroSiemens/cm 1.0 Ohm/-cm

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Conductivity Measurement

• High Purity Water Applications
• Power Semiconductor Manufacturing
• Conductivity Measured as Resistivity in
  MegOhms/cm
• Pure Water 18.18 Meg Ohms/-cm 0.055 uS/cm
• Water Water Treatment Applications
• Industrial Boilers Cooling Towers
• Conductivity Measured in Total Dissolved Solids
  (TDS)

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Conductance of Common Acids, Bases and Salts _at_
25oC
8
Conductivity Measurement

• Each Acid, Base and Salt has Its Own Temperature
  Vs. Concentration Curve
• The Temperature Slope Varies for Different
  Chemicals
• Acids 1.0 - 1.6 /oC
• Natural Waters 2.0/oC
• Bases gt 1.8 - 2.2/oC
• High Purity Water 2.3 - 7.3/ oC

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Specific Conductivity of Sulfuric Acid
10
5.0 Sulfuric Acid Solution
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Change in Temperature Slope/oC
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Conductivity Measurement

• Apply an AC Voltage to Two Electrodes of Exact
  Dimensions
• Acids, Bases and Salts (NaCl) Dissolve in
  Solution and Act as Current Carriers
• The Current Flow is Directly Proportional to the
  Total Dissolved Solids in Solution
• The Physical Dimensions of a Conductivity
  Electrode are Referred to as the Cell Constant
• Cell Constant is Length/Area Relationship
• Distance Between Plates 1.0 cm
• Area of Each Plate 1.0 cm x 1.0 cm
• Cell Constant 1.0 cm-1
• Cell Constant
• Used to Determine the Measuring Range of the
  Analyzer
• Acts as Multiplier
• Used to Calibrate Analyzer
• Determined Using NBS Standards
• Can be NIST Traceable

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Four Electrode Conductivity Cells

• Measures Current and Voltage Drop
• Current Increases with an Increase in Voltage
  Drop Across Electrodes
• Compensates for Minor Coatings on Conductivity
  Electrodes
• Used for Higher Range Measurement

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Inductive Conductivity

• Also Known as Toroidal and Electrodless
• Principle of Measurement
• Two Sealed Wire Wound Coils Electrically Coupled
  by Solution Conductivity
• Advantage
• No Electrodes Exposed to the Measured Solution
• Not Affected by Coating
• Disadvantage
• - 10 Accuracy
• High Range Measurement Only gt 100 uS/cm

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Reverse Osmosis Unit
pH Transmitter
Feed Water
Acid Feed
Feed Water Tank
Conductivity Transmitter
RO Unit
Waste
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Demineralizer Unit
Acid Regeneration
Caustic Regeneration
Conductivity Transmitter
Conductivity Transmitter
Mixed Bed
Anion Bed
Cation Bed
Conductivity Transmitter
To Water Storage
Conductivity Transmitter
Conductivity Transmitter
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Power Utilities Average Number of Analyzers for
Each Demin Unit

• Type Number
• Conductivity 4
• Concentration 2
• pH 1
• Total 7
• Usually 2 per generation unit (make up
  polisher) and built in pairs
• Total X 4 28 Analyzers per Unit
• Two Units Built at a time 56 Analyzers

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Power Utilities Average Number of Analyzers Per
Generating Unit

• Analyzer Type Number
• pH 5
• Specific Conductivity 6
• Cation Conductivity 11
• Condensate Analyzer 1
• Total 23
• Usually Units Built in Pairs 46 Analyzers

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Boiler Blowdown and Condensate Return Lines
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Clean in Place (CIP)
Conductivity Transmitter
CIP Return Lines
Caustic
Process Vessels
Caustic Dilution Tank
Solution Recovery
Conductivity Transmitter
Water