Hach ORBISPHERE 31 Série Manuel D'utilisation Simplifié page 18

Section 7 Troubleshooting
7.1 Oxygen sensor
Problem
Sensor won't calibrate, even
after thorough servicing.
"0000" O levels displayed.
2
Shorter than expected sensor
operation in relatively high
dissolved O concentration.
2
Unexpected or inaccurate
dissolved O readings.
2
7.2 Hydrogen sensor
Problem
Sensor won't calibrate, even
after thorough servicing.
"0000" H levels displayed.
2
18 English
Probable cause
Repeated calibrations go
beyond "expected limits" of
instrument.
Instrument internal barometric
pressure sensor needs
calibration.
Wet membrane interface.
"H S insensitivity" option
2
enabled.
Wrong reading scale "XXXX"
selected for display unit.
High O concentrations
2
generate deposits more
quickly.
Air leak on product sample line.
High residual current.
Probable cause
Repeated calibrations go
beyond "expected limits" of
instrument.
Wrong reading scale "XXXX"
selected for display unit.
Possible solution
MOCA 3600 only: Select
membrane from
"Options/Membrane" menu.
Then, calibrate the sensor.
Calibrate internal barometer
against a certified barometer.
Do not correct for sea level !
Wipe dry with a tissue and re-
calibrate.
Disable on the measuring
instrument.
Change reading scale by
selecting "X.XXX, XX.XX or
XXX.X".
Install a less permeable
membrane. Turn off the
analyzer when sensor is not in
a low O concentration.
2
Set flow rate to 100 mL/min.
Wait until stable, then slowly
double this flow rate.
The stable value of dissolved
O reading must be the same
2
as before. A variation related to
flow rate is a clear sign of an air
leak in the line.
Place sensor in de-aerated
sample; wait for low reading:
Check concentration against
low measurement limit (see
tables in Sensor membrane
specifications on page 3). If
concentration is significantly
higher than low limit, try a
sensor service.
Possible solution
MOCA 3600 only: Select
membrane from
"Options/Membrane" menu.
Then, calibrate the sensor.
Change reading scale by
selecting "X.XXX, XX.XX or
XXX.X".