Hach ORBISPHERE 3658 Basic User Manual page 20

1. Set the gas measurement phase to Gaseous (see
the calibration medium to In a liquid or a gaseous sample at known concentration (see
Calibration medium
2. Connect a source of pure CO
on page 18, and adjust the gas flow exiting from the flow chamber to be in the range of 1 to 5 bar
(it is best to use a pressure close to the application conditions).
3. Press the CAL button. Remember, this button may have been locked out to prevent an accidental
reset (see Locking out the instrument's CAL button
4. A brief clearing message [---] appears.
5. Press CAL again within a 3 second period. The instrument then displays the absolute pressure of
calibration gas (i.e. gauge pressure plus atmospheric pressure).
6. Modify this reading using the Up/Down Arrow keys until the displayed pressure agrees with that
of the gauge plus atmospheric pressure.
If the instrument makes two consecutive measurements with less than 1% difference, it calibrates
against this stabilized value. The LCD then displays the message [CAL] to indicate calibration
has been successfully completed.
If the calibration does not complete, the LCD displays the message [Err]. The reason for this
calibration error is either that the measured gas partial pressure is under 5 mbar, or that a wrong
instrument key was pressed during the calibration steps.
Maintenance
Power supply
It is important to maintain power to the instrument at all times, (either batteries or an external power
supply) to ensure the sensor is continually purged and so prevent damage to the TC sensor chip.
If the ORBISPHERE 3658 instrument is operating on battery power (two standard C-type cells), and
the battery power should drop, a [LO BAT] warning message is displayed in the instrument LCD's
top left corner.
To install the batteries, unscrew the battery cap (on the right side of the instrument) with the tool
provided in the recharge kit, or with a coin or flat bladed screwdriver. Place the cells lengthwise into
the battery compartment (positive end first), and then replace the cap. Refer to the diagram on the
back of the instrument.
Rechargeable nickel-cadmium batteries may be used. Expect about 15 hours of autonomy in
continuous operational use, or 3 weeks in standby. Alkaline batteries provide the longest continuous
use though mercury-free batteries are available that present less of a disposal problem.
Make sure that a fully charged (or fresh) set of batteries is installed before switching on the
instrument.
Sensor maintenance
Maintenance schedule
Sensor maintenance includes membrane replacement and external cleaning to restore the original
sensor sensitivity. This means low running costs and down time reduced to a minimum.
The membrane needs to be replaced once or twice a year depending on application conditions. This
can be tailored accordingly.
Testing the sensor condition
Periodically, visually inspect the sensor head for any deposits. Rinse it under clean tap water, and
dry with a clean tissue.
To verify the sensor, check measurements against a known standard sample value:
• If reading deviation is ±1% of the expected value, no action needs to be taken.
• If deviation exceeds ± 1%, perform a new calibration.
• If deviation exceeds 10% of the original values, replace the membrane.
20 English
on page 16).
gas to the inlet of the flow chamber, as illustrated in
2
Gas measurement phase
on page 16).
on page 15) and set
Figure 3