Calibration And Repair Services - Extech Instruments PH220-C User Manual

Electrode Maintenance and Troubleshooting
Most pH measurement difficulties are caused by the electrode. Careful handling and proper storage of
the electrode will increase measurement accuracy and electrode life.
Electrodes should be rinsed to remove all traces of storage solution, process medium, or previous test
solution.
Electrode Storage
The electrode should be stored in a soaker bottle or wetting cap filled with pH4 buffer. Never store
an electrode in distilled or deionized water as this will cause migration of the fill solution from the
electrode.
Electrode Cleaning
The type of electrode coating that occurs over time will determine the cleaning method. Soft
coatings can be removed by vigorous stirring or by using a squirt bottle. Organic chemical coating
(hard coatings) should be chemically removed. Only in extreme cases should the bulb be cleaned
mechanically.
Troubleshooting an Electrode
Symptom
Long response time or
reading drift
Dry Bulb
Static Charge
Same readings in different
buffers and samples
Erratic LCD display

Calibration and Repair Services

Extech offers repair and calibration services for the products we sell. Extech also provides NIST
certification for most products. Call the Customer Service Department for information on calibration
services available for this product. Extech recommends that annual calibrations be performed to
verify meter performance and accuracy.
Copyright © 2012 Extech Instruments Corporation (a FLIR company)
All rights reserved including the right of reproduction in whole or in part in any form
Cause
Clogged Junction
Strong Alkaline measurement
Deteriorated Gel layer
Protein coating on electrode
surface
Oil, paint, dyes, suspended solids
etc. are on sensor
Organic solvents are coating the
sensor
Dehydrated membrane
Long term storage without wetting Soak electrode tip in wetting cap filled with 1ml
Wiping electrodes
Cracked or broken bulb
Samples have low ionic strength
(lacks salt); e.g. distilled, de-
ionized, boiled, lake water (high
pressure)
ISO-9001 Certified
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Recommendation
Soak in 4.07 M Potassium Chloride (KCl) @
o
60 C for 30 minutes.
Soak in 0.1 M HCL overnight.
Replace electrode.
Soak in 1 gm Pepsin dissolved in 100ml of 0.1
m HCL for 30 minutes or as needed.
Rinse electrode alternately with a materials
solvent and a buffer 7.00.
Organic mole fraction has to be less than 50%
to assure reasonable readings. Limit time of
measurement. Keep probe in the 7.0 buffer
between readings.
Read solution for dry bulb below:
7.00 buffer for 24 to 48 hours
Rinse electrode in 7.0 buffer and blot. Do no
wipe electrode.
Replace electrode. Use bulb guard. Avoid
plunging electrode to bottom of container and
spinning bars. Wetting cap will protect bulb
between tests.
For each 50 ml of sample add 1 drop (50uL) of
SAT. KCl (No alteration in pH will occur using
inert KCl).
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