Operation - BT CGA-411 Operation Manual

3.

OPERATION

A. Overview of Essential Operating Practice
Gas-Sentry detectors are easy to use. However, a few general rules must be followed to
insure reliability and accuracy.
Pump. Gas-Sentry detectors have a built-in pump and depend on this pump for their
operation. If the pump is not functioning normally, the instrument will not function properly. It
is therefore essential to check the pump each time the instrument is first turned on.
Pump Test: Connect the probe you plan to use and select any display. When
the display shows a number, normally zero, block the probe tip with your finger until the display
shows "bloc".
If "bloc" does not appear, there may be a leak along the probe. Tighten all
connections and repeat the test. If a block condition is still not observed, remove the hose and
block the inlet to the instrument. If "bloc" still does not appear, return the instrument to the
factory for repair.
WARNING: The instrument should never be used when "bloc" fails to appear
upon blocking the inlet
Filters. Dust and water-block filters protect the sensors and the pump from dust and
accidental intake of liquid water. Just as a car would not be operated without air and fuel filters,
do not operate a Gas-Sentry detector without a filter on the hose. Operation without this filter
will eventually degrade the pump; it also voids the limited warranty.
From time to time, examine the filter on the hose. If loose dirt has accumulated, shake it
out. Do not poke at the filter with a tool or any other implement which may puncture it. If the
filter is substantially discolored by dirt, replace it.
Zero Check. All sensors drift to some extent over time. Sensor drift is corrected by
using the AUTO ZERO position (see Section 6). Zeroing takes about 30 seconds and is normally
required no more frequently than once a day. It is important that the zero adjustment be done in
clean air, for example, outdoors. If the sampled gas is not clean, a systematic error will be
introduced in subsequent measurements.
Test and Calibration. Gas-Sentry detectors must be checked and calibrated periodically
with gas of known composition. The catalytic combustion and carbon monoxide sensors depend
on catalysts which may loose activity or get poisoned during use. When this happens, there will
be diminished response to gas or CO.
The necessary frequency of calibration depends on actual use and on the concentration of
catalyst poisons in the sampled gas. This concentration is, or course, not generally known.
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