Hach-Lange ORBISPHERE 31xxx Installation and Maintenance - Manual (Page 37)

35
Section 6 Troubleshooting
6.1 Oxygen sensor
6.2 Hydrogen sensor
Table 8 Troubleshooting - Oxygen sensor
Problem Probable Cause Possible Solution
Sensor won't calibrate,
even after thorough
servicing.
Repeated calibrations go beyond
"expected limits" of instrument.
MOCA 3600 only:
Select membrane from
"Options/Membrane" menu. Then,
calibrate the sensor.
Instrument internal barometric
pressure sensor needs
calibration. Calibrate "Barom. Pressure" menu.
Check against a certified barometer. Do
not correct for sea level !
Wet membrane interface.
Wipe dry with a tissue and
re-calibrate.
"H
2
S insensitivity" option
enabled.
Disable from the “Options/Gas" menu on
the measuring instrument.
"0000" O
2
levels
displayed.
Wrong reading scale "XXXX"
selected for display unit.
Change reading scale by selecting
"X.XXX, XX.XX or XXX.X" from.
"Options/Display Units" menu.
Shorter than expected
sensor operation in
relatively high dissolved
O
2
concentration.
High O
2
concentrations generate
deposits more quickly.
Install a less permeable membrane.
Turn off the analyzer when sensor is not
in a low O
2
concentration.
Unexpected or inaccurate
dissolved O
2
readings.
Air leak on product sample line.
Set flow rate to 100 ml/min. Wait until
stable, then slowly double this flow rate.
The stable value of dissolved O
2.
reading must be the same as before. A
variation related to flow rate is a clear
sign of an air leak in the line.
High residual current.
Place sensor in de-aerated sample; wait
for low reading:
Check concentration against low
measurement limit (see tables in
Sensor
membrane specifications on page 10 ). If
concentration is significantly higher than
low limit, try a sensor service.
Table 9 Troubleshooting - Hydrogen sensor
Problem Probable Cause Possible Solution
Sensor won't calibrate,
even after thorough
servicing.
Repeated calibrations go beyond
"expected limits" of instrument.
MOCA 3600 only:
Select membrane from
"Options/Membrane" menu. Then,
calibrate the sensor.
"0000" H
2
levels
displayed.
Wrong reading scale "XXXX"
selected for display unit.
Change reading scale by selecting
"X.XXX, XX.XX or XXX.X" from
"Options/Display Units" menu.
Shorter-than-expected
sensor operation (in
relatively high H
2
).
High H
2
concentrations require
more work from electrochemical
sensor. Shut off analyzer when not needed.
Unexpected/incorrect H
2
readings.
High residual current.
If concentration is significantly higher
than low limit, try a sensor service.