Hach ORBISPHERE 31290TC Manuel D'utilisation Simplifié page 11

6.5 Purge gas system
6.5.1 Purge gas regulator
The role of the ORBISPHERE 29089 gas regulator is to deliver purge gas
filtered at 40 μm. Attach the unit to a suitable bracket, using the M3 threaded
holes on the back. It's position should be vertical ± 5%. The gas flow is
indicated by an arrow on the regulator's body.
Maintenance:
Drain the condensate periodically. Unscrew by hand the drain at the bottom of
the bowl.
If filter is contaminated:
• Turn off the gas supply
• Unscrew the bowl by hand
• Unscrew the black disc at the bottom
• Remove the white composite filter
• Wash under clean tap water, blow dry, and install
6.5.2 Purge gas supply
Make sure there is no interruption in the purge gas supply. The use of a backup gas cylinder and an
automatic changeover valve, that activates when the first cylinder is empty, are recommended.
Use a 6 mm flexible (nylon or PVC) or rigid (stainless steel) line to connect the pressure regulator
and thermal conductivity sensor to the purge gas supply. Swagelok connectors (6 mm or 1/4") are
provided.
A short length of plastic tube is supplied for the purge gas to exit the sensor. To insert, push the tube
firmly into the orifice. To remove, push on the ring surrounding the tube, and pull the tube out. For
certain applications such as waste gas, a 3 mm (1/8") Swagelok fitting is provided for the purge gas
exit, to enable safe evacuation of an eventually hazardous gas.
A source of dry and filtered gas (pure at 99.8%) is required with a flow rate set at 10 to 50 mL/min.,
and a pressure regulated at 2 bar gauge. Do not exceed this, since excess pressure will deform the
membrane and change measurements.
To check the flow rate, put the exit tube into a cup of water. With the instrument turned on, you
should see at least three bubbles per second during the purge cycle.
Do not leave the exit tube in water, as there is a risk that moisture will get sucked back into the
sensor and damage it.
6.5.3 Purge safety backup unit
The gas analyzer must be switched on at all times, and purge gas
must be constantly supplied to purge the sensor cell, to prevent
damage to the sensor electronics.
However, in the event of a mains power outage, the 32605 purge
backup unit ensures that the purge gas supply to the TC sensor is
not interrupted at any time. The cycle is slower than usual (around
one minute), for approximately four days.
The green LED is on as long as the battery charge is OK. The red
LED is on when charging is needed. To save batteries, both LEDs
are out when the backup unit is in use, and mains power is out.
N O T I C E
English 11