Concerns in pH # 4: Reference Contamination

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pH / ORPConductivityDissolved OxygenChlorineStandards

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Concerns in pH # 4:

Reference Contamination

CONTROLS




pH electrodes have porous reference junctions whichallows KCl to migrate through the junction to complete the electrochemical connection and cause a mV signal to be produced.

Since the junction is porous the process can also migrate into the reference causing referencecontamination and premature failure of the pH electrode

PROBLEM




CAUSEAs the process migrates into the reference it attacks theSilver/Silver Chloride wire changing the chemistry which results in the electrode drifting. This is seen as anoffset from zero mV during calibration.




Silver/Silver ChlorideWire

Porous Frit

Solid Spool Piece

Porous ReferenceJunction

Potassium Chloride (KCl)Internal Fill Solution

Typical pH Electrode Internal




Process

With no protection in the reference the KCl and Silver/Silver Chloride wire becomes contaminated very quickly.

Contamination with Standard Internal




Process

By adding the Double Junction, the path length is increased and the rate of contamination is decreased.

Contamination with Double Junction Internal




Process

By adding the Plasticized Reference, which is solid up to 150oC, the migration is slower because it will take longer to migrate through a solid in comparison to a liquid.

Contamination with PlasticizedInternal




Process

By combining the Double Junction and the plasticized Reference, the path length is increased and the rate of contamination is decreased which will give maximum life in applications where reference contamination is a problem. Life expectancy can be months longer when this combination is used.

Contamination with Double Junctionand Plasticized Internal




IC Controls Plasticized, DoubleJunction Reference

Longer Path Length

Slower Migration

Solid up to 150oC

Longer Sensor LifeProven Technology

Superior DesignBetter Results

Concerns in pH # 4: Reference Contamination

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