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UGA Series Universal Gas Analyzers
Calibration and Input Design
5 –
materials commonly used in gas chromatography. The following
sections discuss details of the flow of the sample gas within the
instrument.
The pressure and flowrate of the sampled gas can be calculated with
simple formulas. The calculations here assume that gases behave
ideally, which is a reasonable approximation at the temperatures
and pressures involved. Actual system performance compares
well with these simple calculations.
The pressure drop across a length of tube is related to the flowrate
and dimensions by:
()
where Q is the throughput, C is the conductivity, and ∆P is the
pressure drop. Throughput is a measure of mass flowrate com
-
monly used in vacuum systems. Typical units for Q are mbar liter
s
-
, which unless stated otherwise, implies a standard temperature.
At STP (273.5 K and 03.25 mbar) mbar liter s
-
is equal to .03
cm
3
s
-
(sometimes abbreviated sccs). The conductivity of various
geometries is calculated with the standard formulas available in
texts discussing vacuum (see References).
The pressures and flow at every point in the system is determined
by applying equation 1 to each section of tube. A simplified flow
schematic of the UGA is shown below.
5.3.1 Flow Calculations
(
)
Q C P
P
C P
in
out
=
−
= ∆
