All-Hands Meeting

What is pH?What is pH?

pH is the measurement of the Hydrogen Ion concentration in a particular solution. Indicates the Acidity or Alkalinity of a solution.u Why is pH measured?

² Used as a process control parameter.² Most reliable specific Ion measurement.² Least maintenance intensive specific Ion

measurement.

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What is pH ?What is pH ?

•pH = - Log [H+]

100 10-1 10-2 10-3 10-4 10-10 10-13 10-1410-1210-5 10-6 10-7 10-8 10-9 10-11

10010-110-210-310-410-1010-1310-14 10-12 10-510-610-710-810-910-11OH-

H+

pH Scale

1 2 3 4 5 6 7 8 9 10 11 12 13 140

Acid Base

Neutral

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The pH MeasurementThe pH Measurement•pH Measuring Components

– Measuring Electrode– Reference Electrode– Temperature Compensator– Analyzer (Transmitter)

•How the Measuring System worksuThe glass electrode develops a potential directly related to the

Hydrogen Ion concentration of a solution. The potential is measured as (mV) across the glass membrane.

uThe Reference electrode is necessary as a constant potential for comparison against the measuring electrode. It also completes the electrical circuit - Provides liquid wire!

uThe change in voltage/Hydrogen Ion concentration will be directly proportional to the change in pH.

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pH Simplified!pH Simplified!• pH system works similar to battery -

The Glass electrode provides a constant voltage (steady state), while the reference builds resistance with time/usage.

• As Reference electrode ages the internal resistance (across Junction) increases

• Resistance across Junction increases until measurement signal lost - High Impedance!

• After initial calibration, 90% or more of calibration offset is due to reference deterioration.

V = Constant VoltagePotential

V = IR

V = Glass electrode output

R = Reference electrode

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Measuring ElectrodesMeasuring Electrodes

• Glass: Most Common - Used in 95% or more of all applications.

• Solid State - Utilizes a Solid State Chip rather than glass. Example: ISFET Technology - Currently used in 2%-3% of all applications

• Antimony - Silver white metal (Similar to Lead). Used in applications where glass will not! Example: (HF) Used in 1%-2% of all applications.

Antimony Electrode

Solid State Electrode

Glass Electrode

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Glass Measuring ElectrodeGlass Measuring Electrode

H+

KCl Electrolyte

Ag/AgCl Electrode

H+

Glass Membrane

High Impedance

Coaxial Cable

H+

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Durafet pH ElectrodeDurafet pH ElectrodeLow ImpedanceConnector

FastRespondingTemperatureSensor

ReplaceableCeramicReferenceJunction

QuickDisconnectCable

Ag/AgClElement

RefillableSaturatedKCl Gel

RuggedDurafetSensor

CounterElectrode

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Troubleshooting the Electrode Troubleshooting the Electrode SystemSystem

•Reference electrode is the weak link in the measurement system in 90% of all applicationsuReference open to the process - porous junctionuTypical modes of reference failure:

² Plugging² Fouling² Poisoning² Depletion² Pressure spikes

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Reference ElectrodesReference Electrodes• Diffusion (Slurry/Gel) - Used

in 95% or more applicationsuSingle JunctionuDouble JunctionuTriple Junction

• Flowing - Used in 5% or less applicationsuSalt BridgeuBellowmatic

• Solid State -Currently unavailable

Single Junction

Double Junction

Triple Junction

Ion Sensitive Coating

Non-Porous Reference

Ceramic body

Solution ground

l

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ProblemJunction Type

Plugging Fouling Poisoning Depleting Pressure InitialCost

Ease ofUse

LongTermCosts

DIFFUSION JUNCTION REFERENCE ELECTRODESingle Junction 2 3 3 2 3 1 1 3Double Junction 2 3 2 2 3 1 1 2Triple Junction 2 3 1 3 3 1 1 2

FLOWING JUNCTION REFERENCE ELECTRODESalt Bridge 1 1 1 1 2 2 3 1Bellomatic 1 1 1 1 1 2 2 1Solid State 1 2 1 1 1 3 1 1

RANKING:

1=GOOD

2= FAIR

3==POOR

l

Reference Electrode Selection GuideReference Electrode Selection Guide

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Reference Electrode Diffusion TypeReference Electrode Diffusion Type

KCl ElectrolyteSaturated

Gel

Standard Wire

Ag/AgCl Electrode

Porous Junction

K+

Cl-

K+ Cl- mVJunction Potential

offset during calibration(Asymmetry)

K+

Cl-

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Double Junction Double Junction Reference ElectrodeReference Electrode

Diffusion TypeDiffusion Type

KCl ElectrolyteSaturated

Gel

Standard Wire

KCl ElectrolyteSaturated

Gel

Ag/AgCl Electrode

Porous Junction

K+

Cl-

K+ Cl-

No Silver Ion

Internal Junction

K+ Cl-

Ag+

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Triple Junction Reference Triple Junction Reference Electrode Diffusion typeElectrode Diffusion type

K+ Cl-

K+Cl-

Ag/AgCl

K+ Cl-

K+

Cl-

K+Cl-

Cl-

Standard Wire

Saturated KCLElectrolyte Gel

No Silver Ion

Porous Junction

Internal Junction

Ag/AgCl Wire

Saturated KCL orAmmonium Nitrate

Electrolyte Gel

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Reference ElectrodeReference ElectrodeFlowing TypeFlowing Type

Ag/AgCl Electrode

Flowing Junction

Standard Wire

K+

Cl-

K+ Cl-

KCl Electrolyte2 Normal

To Reservoir

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Reference “ Rules of Thumb”Reference “ Rules of Thumb”•Typical Applications - Expect to replace (3)

Reference electrodes for every (1) Measuring•Harsh Applications - Expect to replace (10)

Reference electrodes for every (1) Measuring•Minimum Life expectancy - Junction Poisoning

uSymptoms to be aware of:² Severe discoloring of Junction

• Junction turns brown or black in color• Discoloration not removed when cleaned

•Remember - When in doubt think...........uReference!

² Reference!• Reference!

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The Bellowmatic electrodeThe Bellowmatic electrode

•Flowing JunctionuInternally pressurized by bellows assembly

•Pressure compensatinguBellows floats with process pressure changes

•Self containeduNo external connections/tubes/reservoirs

•Unique to the industryuOne of a Kind!

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The Bellowmatic SolutionThe Bellowmatic Solution•What problems can the Bellowmatic solve?

uPlugging ² Positive pressure prevents internal build-up.

uFouling² Positive pressure prevents external build-up.

uPoisoning² Positive pressure prevents process migration.

uDepletion² Positive pressure prevents dilution.

uPressure Spikes² Floating bellows compensates for process spikes.

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Where each Reference electrode Where each Reference electrode type type could could operateoperate

0

20

40

60

80

100

All pH Applications

(%)

Single

Double

Triple

Salt Bridge

Bellowmatic

Solid State

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Where each Reference electrode Where each Reference electrode type type shouldshould operateoperate

010

203040

506070

8090

100

All pH Applications

(%)

Solid State

Flowing - Salt Bridge

Flowing - Bellowmatic

Diffusion - All types

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Test QuestionsTest QuestionspH

1) What should the output (Millivolts) of a pH measuring electrode be in a 7 buffer?

2) What should the Asymmetry of a new reference electrode be after calibration?

3) In a typical application how many reference electrodes will be replaced per glass electrode?

4) What is the reference mode of failure that causes the junction to turn brown or black?

5) What company makes an electrode like the Bellomatic?

6) What are two applications ideal for using the Bellomatic?

CONDUCTIVITY7) What “Rule of Thumb” value (uS/cm) defines when

to use Inductive vs. Contacting conductivity?8) What factor is used to convert from uS/cm to

uMho/cm?9) What two industries were DC400 designed for?10) What other companies make Dual cell analyzers?11) How many bore sizes are available for the IC40

sensor?

12) Why is the IC40 stable with process temperature changes?

13) The 5X5 matrix is compensating for what effect on the solution?

• match the analyzer/measuring technology that should be used with the following applications: a = DC; b = SC; c = IC

14) Reverse Osmosis system15) Demineralizer Regeneration System16) Softener17) Demineralizer Outlet

ZIRCONIA OXYGEN18) Why is our cell resistant to attacks from flue

gases?19) How does the competition bond the platinum to

their ceramic cells.20) What are two advantages of using reference air as

one of the calibration gases?

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Test QuestionsTest QuestionspH

1) What should the output (Millivolts) of a pH measuring electrode be in a 7 buffer? (Zero Millivolts)

2) What should the Asymmetry of a new reference electrode be after calibration? ( + or - 20 Millivolts)

3) In a typical application how many reference electrodes will be replaced per glass electrode? (3 to 1)

4) What is the reference mode of failure that causes the junction to turn brown or black? (Poisoning)

5) What company makes an electrode like the Bellomatic? (None)

6) What are two applications ideal for using the Bellomatic? (Students Choice)

CONDUCTIVITY7) What “Rule of Thumb” value (uS/cm) defines when to use

Inductive vs. Contacting conductivity? (100 uS/cm)8) What factor is used to convert from uS/cm to uMho/cm?

(None - both units have same value)9) What two industries were DC400 designed for? (Power &

Semiconductor)10) What other companies make Dual cell analyzers?

(Rosemont, L&N, Thornton, Foxboro, Signet)11) How many bore sizes are available for the IC40 sensor?

(One)

12) Why is the IC40 stable with process temperature changes? (Matched Coils)

13) The 5X5 matrix is compensating for what effect on the solution? (Temperature)

• match the analyzer/measuring technology that should be used with the following applications: a = DC; b = SC; c = IC

14) Reverse Osmosis system (DC or a)15) Demineralizer Regeneration System (IC or C)16) Softener (DC or a)17) Demineralizer Outlet (SC or b)

ZIRCONIA OXYGEN18) Why is our cell resistant to attacks from flue gases?

(Molecular Bonding)19) How does the competition bond the platinum to their

ceramic cells. (Adhesive Bonding)20) What are two advantages of using reference air as one of

the calibration gases? (Cost and true zero of cell output)