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Concerns in pH # 4: Reference Contamination PowerPoint PPT Presentation


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IC. CONTROLS. Concerns in pH # 4: Reference Contamination. PROBLEM. pH electrodes have porous reference junctions which allows KCl to migrate through the junction to complete the electrochemical connection and cause a mV signal to be produced.

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Concerns in pH # 4: Reference Contamination

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Concerns in ph 4 reference contamination

IC

CONTROLS

Concerns in pH # 4:

Reference

Contamination


Concerns in ph 4 reference contamination

PROBLEM

pH electrodes have porous reference junctions which

allows 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 reference

contamination and premature failure of the pH

electrode


Concerns in ph 4 reference contamination

CAUSE

As the process migrates into the reference it attacks the

Silver/Silver Chloride wire changing the chemistry

which results in the electrode drifting. This is seen as an

offset from zero mV during calibration.


Concerns in ph 4 reference contamination

Typical pH Electrode Internal

Silver/Silver Chloride

Wire

Potassium Chloride (KCl)

Internal Fill Solution

Porous Frit

Solid Spool Piece

Porous Reference

Junction


Concerns in ph 4 reference contamination

Contamination with Standard Internal

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

Process


Concerns in ph 4 reference contamination

Contamination with Double Junction Internal

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

Process


Concerns in ph 4 reference contamination

Contamination with Plasticized

Internal

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.

Process


Concerns in ph 4 reference contamination

Contamination with Double Junction

and Plasticized Internal

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.

Process


Concerns in ph 4 reference contamination

IC Controls Plasticized, Double

Junction Reference

Longer Path Length

Slower Migration

Solid up to 150oC

Longer Sensor Life

Proven Technology

Superior Design

Better Results


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