Troubleshooting The Orp Electrode - Hach EC1000 Instruction Manual

9.3 Troubleshooting the ORP Electrode

Symptom Probable Cause
mV reading does Reference electrode/preamp
not correspond to offset. The Ag/AgCl reference
cited mV value for half cell uses a 1.5 M KCl in
standard. 40% glycerol electrolyte
solution. This has a potential
of 32 +10 mV versus SCE. In
addition, the electrode
preamp can contribute a +35
mV offset. (See Table 2 on
page 27).
Fouled sensor
ORP sensor is internally
shorted
Reference has become
poisoned
The mV readings Air in the reference line
are erratic.
Air in the sample line
ORP Sensor is broken.
There is no
electrolyte flow.
Table 17 Troubleshooting the ORP Electrode
Corrective Action
Zero the preamp. See Section 2.3.3.1 Preamp Zero .
Clean electrode in 1 M HCl. (See Section 8.1.8 pH Electrode Cleaning )
Remove ORP sensor. Inspect it for wetness inside the glass stem. If wet,
replace. If dry, verify that two O-rings are being used, inspect them for
damage and replace if necessary. Completely dry both the inside of the
electrode socket and outside of the sensor assembly. Reinstall. (Refer to
Section 8.1.3 Sensor Replacement ).
Flush with large amounts of reference electrolyte. If this is not successful,
replace the entire electrode.
Verify that electrolyte is exiting the reference outlet. Wipe the end of the
electrode dry, and observe the reference outlet tube with the pump running
and the priming tee in the RUN position. A full drop of electrolyte should
become visible within 5 minutes (5 pumps). If a drop does not appear,
purge the system (see Section 6.3 Purging the System ) (also see
Symptom: No electrolyte flow).
If a pocket of air passes over or gets trapped at the end of the electrode, the
reading becomes momentarily erratic. This usually is remedied by
reorienting the electrode so that air bubbles do not block the sensor
(see Section 5.5 Installing the pH/ORP Electrode ).
Remove the ORP sensor from the electrode body and inspect it for wetness
within the glass stem (see Section 8.1.3 Sensor Replacement ) If wet,
replace sensor. If dry, verify that two O-rings are being used, inspect them
for damage and replace if necessary. Completely dry both the inside of the
electrode socket and outside of the sensor assembly. Reinstall. (Refer to
Section 8.1.3 Sensor Replacement ).
See Section 9.2 Troubleshooting the pH Electrode
98