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D e t e c t i o n
User Manual
Multi-Gas detector POLI
D e t e c t i o n
17
4.4.1.4 PTFE CONNECTING TUBING FOR REACTIVE GASES
For reactive gases including ozone, chlorine, chlorine dioxide, hydrochloric acid, hydrofl uoric acid,
and absorbable gases such as most VOCs, it is critical to use inert connecting tubing such as WatchGas
Last-o-more hose and make connections as short as practical. More fl exible variants such as PTFE-lined
Norprene or PTFE-lined Tygon are suitable alternatives. For most other gases, including standard 4-gas
mixes with carbon monoxide, hydrogen sulfi de and methane, other tubing can be used.
4.4.1.5 OTHER ATTACHMENTS
It is always most accurate to calibrate the POLI with all attachments in place in the same manner as
in the fi eld measurements. For example, normally a fi lter should be used on the POLI inlet for both
measurements and calibration. However, if a fi lter is not used during measurement (as preferred
in a few cases of highly reactive gases) then no fi lter should be used during calibration. Similarly, if
extension tubing is being used during sampling, a more accurate calibration is obtained if the tubing
is also attached during calibration. This method accounts for any small changes made to the gas
concentration by the attachment(s).
4.4.2 FRESH AIR (ZERO) CALIBRATION
Zero calibration should precede span calibration and be done in clean air with 20.9% oxygen. This
procedure determines the zero points of most sensors and the span calibration for the oxygen sensor.
No gas connections are required if the ambient air contains no detectable contaminants.
In Confi guration Mode, enter the Calibration menu and select ‘Fresh Air Calib’ to show the selected
sensor list. De-select any sensor(s) not wanted to be zeroed ([ / ](Change)). Start the zero calibration
by pressing [+/OK] ‘ ’ to initiate the 30-second zero calibration count-down.
NOTE: The POLI also off ers the option for a zero calibration every time the instrument is powerd on.
Select the Zero at Start option in WatchGas Suite
Diff usion Instruments
Diff usion instruments have a black cap covering the Luer connector to protect the unit from dirt and
moisture. This cap must be removed to attach the Luer fi tting and connected tubing leading to the
gas supply. (Internal channels distribute the gas to each sensor, even though during measurements
the gas enters and leaves through the four fi lters on the face of the POLI.) The gas fl ow should be low,
between 0.2 and 0.3 LPM to avoid pressure build-up in the sensor channels. Do not use a T-connector
or demand-fl ow regulator with diff usion sampling.
