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A detector can be tested with "bump" gas. Such tests only verify that the gas sensor(s) are
in operating condition; to adjust their sensitivity they must be calibrated.
A detector can be automatically calibrated in less than one minute using Bascom-Turner's
calibration gas (2.5% methane and 100 ppm CO in air). Given the ease and speed of automatic
calibration, it pays to calibrate as frequently as possible, and certainly, no less than monthly.
Calibration with pure gas (methane) is generally not required more frequently than once a year
unless the composition of the system gas is known (or suspected) to have changed significantly.
Accuracy. A properly operating and calibrated detector will respond to gas, CO, H
and oxygen with the specified accuracy. If combustible gases other than the gas used for
calibration are likely or suspected, the instrument cannot be relied upon to give a proper
indication of their concentration and hence of how close to their combustible limits they may be.
For example, the detector responds quite differently to gasoline, methane, and propane.
Accordingly, readings of % GAS refer only to the calibration gas and can be relied upon only in
this respect in assessing an atmosphere sampled by the detector. Furthermore, concentrations
displayed by the detector refer to a local sample at the tip of the probe. Low gas concentrations
at one place do not necessarily mean that the gas concentration is low throughout a much wider
area.
WARNING:
The detector responds to the four gases for which it was designed. Other
toxic or dangerous gases are not detected or monitored.
B.
Operational Description
To conserve the batteries, the switch should be in the OFF position when the detector is
not in use. A display can be selected in any order from any position of the switch. When a
display is selected from the OFF position, the detector requires about thirty seconds for warm-up.
During this period, the display shows sequentially a single dot (when the microprocessor
becomes operational) followed by two dots while the on-board memory is tested, and by the
symbol for the selected display ("GAS", "CO", "O2"). After warm-up is complete, the display
shows readings for the appropriate gas.
All detected gases are monitored at any setting of the selector switch. The selector
switch merely determines the gas whose concentration is displayed.
To Display Gas with the "% GAS" Display. Connect an appropriate probe to the dust
and water-block filter and set the selector switch to "% GAS". After warm-up, the display shows
the concentration of gas (methane) in air in percent by volume. If the air is clean (contains no
methane), the display should read zero. If it does not, switch to "AUTO ZERO". After
automatic adjustment of zero is complete (the display shows "End"), return the switch to the "%
GAS" position.
5
S,
2
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