Hach EC1000, Instruction Manual

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9.3 Troubleshooting the ORP Electrode
Table 17 Troubleshooting the ORP Electrode
Symptom Probable Cause Corrective Action
mV reading does
not correspond to
cited mV value for
standard. Reference electrode/preamp
offset. The Ag/AgCl reference
half cell uses a 1.5 M KCl in
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).
Zero the preamp. See Section 2.3.3.1 Preamp Zero.
Fouled sensor Clean electrode in 1 M HCl. (See Section 8.1.8 pH Electrode Cleaning)
ORP sensor is internally
shorted 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).
Reference has become
poisoned Flush with large amounts of reference electrolyte. If this is not successful,
replace the entire electrode.
The mV readings
are erratic. Air in the reference line 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).
Air in the sample line 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).
ORP Sensor is broken. 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).
There is no
electrolyte flow. See Section 9.2 Troubleshooting the pH Electrode