conductivity (1)

File Name: Conductivity.pptFeb 2001

Conductivity Theory

Applied to Proper Hardware Selection


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


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-


Typical Conductivity Values

0.055

0.5

1

50

50,000

355,000

0 1 100 10,000 1,000,000

Ultra Pure Water

Distilled Water

Boiler Feed Water

Mains Water Supply

Sea Water

10% NaOH



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



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)


Conductance of Common Acids, Bases and Salts @ 25oC

0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

% by Weight

Mil

liS

iem

ens/

cm

Sodium Chloride Potassium Chloride Sodium Hydroxide

Hydrochloric Sulfuric Acid Nitric Acid



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 > 1.8 - 2.2%/oC• High Purity Water 2.3% - 7.3%/ oC


Specific Conductivity of Sulfuric Acid

0

500

1000

1500

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

% Concentration

mS

/cm

25C 60C


5.0% Sulfuric Acid Solution

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0 4 10 16 21 27 32 38 43 49 54 60 66 71 77 82 88 93 93

Degrees C

mS

/cm


Change in Temperature Slope/oC

012345678

0 10 20 25 30 40 50 75 100

Temperature

Tem

per

atu

re S

lop

e

Ultra Pure Water Sodium Chloride



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

Na+

Cl-


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

V


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

> 100 uS/cm


RO Unit

Reverse Osmosis Unit

Acid Feed

FeedWaterTank

Conductivity Transmitter

pH TransmitterFeed Water

Waste


Demineralizer Unit

CationBed

Mixed Bed

AnionBed

To Water Storage

Acid RegenerationCaustic Regeneration

ConductivityTransmitter






Type NumberConductivity 4Concentration 2pH 1Total 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

Power Utilities Average Number of Analyzers for Each Demin Unit


Analyzer Type NumberpH 5Specific Conductivity 6Cation Conductivity 11Condensate Analyzer 1Total 23

Usually Units Built in Pairs = 46 Analyzers

Power Utilities Average Number of Analyzers Per Generating Unit


Boiler Blowdown and Condensate Return Lines

SteamDrum

Heat Exchanger

Condensate Return

Top Blowdown Line


Blowdown Valve

Steam Header


Waste

MudDrum

Manual Blowdown ValveDo Not Automate !

Feed WaterTank

Flash Tank


Clean in Place (CIP)ConductivityTransmitter

CausticDilution

Tank

SolutionRecovery

ProcessVessels

Water


CIP Return Lines

Caustic

conductivity (1)

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