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MAN0585.P65
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2. USING THE MINIGAS MK5
2.8
ZERO SETTING
2.8.1
Checking Zero Readings
With the Minigas Mk5 switched on in a clean, fresh air
environment, check the initial instantaneous indications. These
should be:
Oxygen
20.9% VOL.
Toxic gases
0ppm, 0.0ppm, 0% or 0.0%.
Explosive gas
0% LEL or 0.0% VOL.
Carbon dioxide
0.1
±
0.2% v/v.
If the indications are different, then, within certain limits, it is
possible to zero them using the optional AutoZero facility.
Note: The zero checking facility and the AutoZero software
option are not available on Go/NoGo instruments (see
Section 2.11).
2.8.2
AutoZero Facility
WARNING
As there is an appreciable, variable concentration of CO
2
in clean air, the autozero function must not be used on
instruments fitted with carbon dioxide sensors.
The flow diagram (Figure 1) shows an AutoZero/Autospan box.
If the AutoZero software option is enabled, the instantaneous
gas readings can be reset to zero (or 20.9% for oxygen) during
the initial 60-second period after switch on.
Note: It is important that the Minigas Mk5 is AutoZeroed only in
clean, fresh air.
AutoZero the Minigas Mk5 by selecting the INST (
) display
and applying a long press to the I/O button. The readings are
zeroed on the release of the button.
