Hach ORBISPHERE 3654 Basic User Manual page 24

Section 8 Maintenance
8.1 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 3654 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.
8.2 Sensor maintenance
8.2.1 Maintenance schedule
Service 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.
Note: If you are not familiar with ORBISPHERE sensor servicing, your Hach representative will be glad to assist
you
8.2.2 Testing the sensor condition
Periodically, inspect visually 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.
Carry out the maintenance in a clean dry place in order to avoid damaging the sensor's precision components,
and also to prevent water or humidity from getting into the sensor.
8.3 Membrane replacement
After replacing a membrane, the sensor must always be recalibrated. Allow the sensor to settle for
30 minutes in measurement phase to allow measurements to stabilize, before performing the sensor
calibration.
8.3.1 Removing the membrane
It is recommended to leave the sensor in place in the instrument when changing the membrane. It is
not necessary to remove it.
To avoid any liquid coming into contact with the TC sensor chip via the purge path, check that the
flow chamber is completely empty of any liquid sample. Then remove the flow chamber from the
sensor by turning the flow chamber locking nut counter-clockwise and gently lifting it off the sensor.
Refer to Instrument overview
To remove the membrane, follow the steps below:
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C A U T I O N
on page 8.