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MODEL SOLU COMP II SECTION 8.0
TROUBLESHOOTING
FIGURE 8-7. Checking for a Poisoned Reference
Electrode.
Refer to the sensor wiring diagram to identify the reference leads.
A laboratory silver/silver chloride electrode can be used in place
of the second sensor.
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8.9 MEASURING REFERENCE VOLTAGE
Some processes contain substances that poison or
shift the potential of the reference electrode. Sulfide
is a good example. Prolonged exposure to sulfide
converts the reference electrode from a silver/silver
chloride electrode to a silver/silver sulfide electrode.
The change in reference voltage is several hundred
millivolts. A good way to check for poisoning is to
compare the voltage of the reference electrode with
a silver/silver chloride electrode known to be good.
The reference electrode from a new sensor is best.
See Figure 8-7. If the reference electrode is good,
the voltage difference should be no more than
about 20 mV. A poisoned reference electrode usu-
ally requires replacement.