Appendix
A
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Channel Specific Settings and Features
Out-Of-The-Box Electrode Check
Follow this procedure to perform a quick evaluation of a new pH electrode and help diagnose a
defective pH electrode.
1.
Remove the pH electrode from the box.
2.
Connect the pH electrode to the BNC input on the pH/LogR module connected with the
V
ERSA
S
TAR
meter.
3.
If needed, select LogR as the temperature source:
a.
In the measurement mode, press the
setup key
b.
Press the ◄ or ► key to highlight Channel # (the channel number the LogR module is
connected with) and press the
f3 (Select) key.
c.
Press the ◄ or ►key to highlight Temperature and press the
f3 (Select) key.
d.
Press the
▲ or
▼ key to highlight Temperature Input and press the
◄ or
► key to
highlight the channel number the LogR module is connected with (i.e. Ch2-LogR).
e.
Press the measure (esc) key to return to the measurement mode.
4.
Read the resistance value shown on the measurement display.
a.
A resistance value of 0 indicates that the pH electrode may be defective.
b.
A resistance value other than 0 indicates the pH electrode is responsive. Prepare the
pH electrode according to the instructions in the electrode user manual. Perform the
initial electrode check when the electrode is ready.
Initial Electrode Check
For the most pH electrode diagnostics benefits from the V
ERSA
S
TAR
meter with pH/LogR
measurement module, establish a regular schedule of resistance testing with the pH electrode.
Perform an initial check of the pH electrode resistance and record the temperature and
resistance value in the provided table, or perform a LogR temperature calibration and export the
calibration information to a computer or printer.
1.
Rinse the pH electrode with deionized water and blot dry with a lint-free tissue.
2.
Insert the pH electrode into the solution and gently stir the solution.
3.
Record the temperature and resistance value for reference.
The pH-sensing bulb thickness and diameter vary among pH electrodes, resulting in normal
variations in resistance values.
In most cases, the initial value is not a definitive test of electrode
condition except in extreme cases such as the initial low readings information described below.
When changing pH electrodes, do not be alarmed if the resistance varies dramatically from your
previous electrode.
Initial Low Readings – If the resistance is below 1 MΩ in a solution at room temperature (22 to
27 °C), it indicates a damaged pH electrode. In this case, the electrode will most likely need to
be replaced.
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Meter User Manual
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Appendix
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Channel Specific Settings and Features
Periodic Electrode Testing
Periodically check the pH electrode resistance following the steps above and record resistance
values in the provided table. Diagnostic testing at 25 °C is ideal, due to the resistance
stability
at this temperature. It is important to keep as many sampling variables constant as possible to
get the most out of the periodic resistance testing. The resistance reading is fully dependent on
temperature. When testing, use the same solution at a known, stable temperature each time
and measure around the same temperature each time.
Small Variances in Resistance – Resistance will typically increase as
the pH-sensing bulb
ages. This is no cause for concern. Over time, this can lead to slower response rates, slope
degradation and reduced immunity to noise. By keeping track of the change in resistance
(delta, as listed in the table as an example), this information may be used to determine when to
replace the pH electrode before
failure occurs, eliminating down time.
Large Decreases in Resistance – When the pH-sensing glass membrane resistance is more
than ten times lower than the expected resistance value at a given temperature, it is often an
indication of a crack in the bulb or shorting of the electrode, leading to a total failure in function.
If you see this type of change in the resistance reading, most likely no further testing or care will
resolve the problem and a new pH electrode will be needed.
Increases in Resistance – As the electrode ages, the resistance of the glass pH-sensing bulb
increases. Eventually, the aging of the electrode, and visible increase in resistance, manifests
in a slower response rate, low slope, and reduced immunity to noise. At some point, the
resistance becomes “super high”. The pH electrode diagnostics from the V
ERSA
S
TAR
meter
with pH/LogR measurement module help pinpoint causes of reduced pH electrode performance
and quickly show the effectiveness of cleaning and care processes.
·
If the resistance values are not out of expected range, but electrode response continues to
be slow or erratic, these effects may also be seen because of reference clogging or
contamination. Follow the cleaning procedures in the pH electrode user manual.
·
If the resistance value between checks increases substantially higher, the fill solution may
be depleted. Follow the cleaning and filling procedures in the pH electrode user manual.
·
If the resistance values show a “super high” resistance, cleaning and care may improve
performance, but will not be able to return the probe to like new condition. Consider
purchasing a new electrode.
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Thermo Scientific