4.3 Set up the background gas
4.3.1 Selecting the type of gas
The
Aurora H2O
TDLAS is normally calibrated to a standard
gas mixture that is representative of “typical” natural gas.
The primary components and concentrations of this gas
mixture are:
Component
Concentration
Methane (CH4)
90.0%
Nitrogen (N
2
)
6.0%
Carbon dioxide (CO
2
)
4.0%
The process background gas is selectable from the
settings menu.
• For normal operation in natural gas service, STD
should be selected as the background gas.
• For verification testing in pure methane, select CH4.
• If verifying in Nitrogen with a known moisture
concentration, N
2
should be selected as the
background gas.
The
Aurora H2O
displays
the selected background
gas an indicator in the
upper right corner of the
LCD, adjacent to the status
message.
Unless otherwise requested, the
Aurora H2O
is shipped from
the factory configured for methane operation.
To change the type of
background gas, from
the settings menu select
gas and press enter. The
following screen appears.
From the gas data menu,
select background and
press enter. The following
screen appears.
Use the arrow keys
to select the desired
background gas,
and press enter. The
background gas selection
is now complete. Press
cancel to return to the
display page.
NOTE:
Selecting either
gas1 or gas2 enables the
label menu item. This
menu opens a keyboard
display that allows the
user to change the ‘gas1/2’
label to one of their own
choosing. Entering the
Label menu requires the
user passcode (2719).
4.3.2 Setting the Z factor
The
Z factor
is a number that accounts for the non-ideal
compressibility of natural gas, and is vital for accurate
calculation of mass/volume (lbs/MMSCF, mg/m
3
).
To set the Z factor, from
the gas data menu, select
Z factor and press enter.
The following screen
appears.
Use the left and right
arrow keys to select each
digit to be changed. Use
the up and down arrow
keys to change the value.
When finished, press enter.
The screen returns to the
settings menu.
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