HACH LANGE ORBISPHERE 3654, User Manual, Page: 14 / 58

12
Installation
3.3 Atmospheric pressure equilibrium
As soon as you receive the instrument, it will be necessary to ensure the interior and exterior of
the instrument are both at the same atmospheric pressure. It is probable that during shipment
these pressures will become different.
To ensure the pressures are equal, simply press the relief valve switch located on the top of the
instrument (see
Figure 1 on page 11 ) and hold it down for about 5 seconds before releasing.
3.4 Sensor installation
The TC sensor connects to the instrument base through a 10-pin LEMO connector. A locking
pin holds the sensor in place.
Both the membrane-covered TC sensor and the flow chamber are shipped pre-installed on the
instrument. It will, however, be necessary to remove the flow chamber when servicing the
sensor. For details refer to
Sensor maintenance on page 41 .
3.5 Purge gas connection
It is critical that the TC sensor has a supply of purge gas running before operating the system.
The TC sensor, when exposed to a liquid sample, will become damaged if the purge gas is not
running. CO
2
is used to purge the N
2
sensor and N
2
or CO
2
is used to purge the H
2
sensor. A
cylinder located at the bottom of the instrument supplies the purge gas. This cylinder is refillable
(see
Purge gas cylinder refill on page 45 ).
The TC sensor is purged cyclically. In measurement mode, a cycle consists of a 4 second purge
followed by 16 seconds of measurement. When the instrument is in standby, the purge time is
the same, followed by a 17 minute delay. During the purge time, the flow rate varies, depending
on the pressure inside the cylinder. At least four bubbles should exit from the purge gas exit
during the purge time.
The purge gas input to the sensor uses a Tygon tube (4 mm outside/2 mm inside diameter, 110
mm long) that attaches to the base of the sensor. Refer to the exploded sensor diagram in
Figure 2 above.
The hole in the side and near the base of the sensor is the purge gas exit. To check the purge
gas flow rate, push the supplied nylon tubing into this hole, to its limit. To disconnect it again,
press on the ring surrounding the tube and pull out.
To check the purge gas flow rate, immerse the end of this tubing in water and switch on the
instrument. Gas should flow intermittently out of the tube.
Note:
During normal operation, and especially when the instrument is in standby mode, ensure that the exit
of the purge gas tube is exposed to the atmosphere and not in contact with any liquid or hard surface.
Figure 2 TC sensor - exploded view