Hach ORBISPHERE 3654 Basic User Manual page 9

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.
Refer to Sensor maintenance
Figure 2 TC sensor
1 Purge gas inlet
2 Output connection to portable instrument
3 Purge gas outlet
4.6 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 is used to purge the N
2
at the bottom of the instrument supplies the purge gas. This cylinder is refillable. Refer to
cylinder refill on page 27.
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 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.
4.7 Connections
4.7.1 External power supply (optional)
The instrument is usually powered by the batteries supplied. You can, however, power it from an
external power source using the model 32939 power supply adaptor as illustrated in
on page 24.
sensor and N or CO
2 2
4 External temperature sensor
5 Storage cap
is used to purge the H
2
Figure 2 on page 9.
sensor. A cylinder located
2
Purge gas
Figure 3.
English 9