Instruction manual

MODEL Xmt-P SECTION 10.0

TROUBLESHOOTING

10.9 MEASURING REFERENCE VOLTAGE

Some processes contain substances that poison or shift the poten-

tial 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 elec-

trode. 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 10-4. If the reference electrode is good, the voltage differ-

ence should be no more than about 20 mV. A poisoned reference

electrode usually requires replacement.

FIGURE 10-4. 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.