Section 4
Theory of Operation 4-13
This is done by iterating Equation 4-15, starting with
T
=
pT
, until the value of
T
stops
changing. (If the pressure correction is off, then no iteration is needed).
S
o
is computed from
SS
o
T
= −
α
α
α
1
4-16
Two Point Spanning (Set S
o
and S
1
)
The two point span will not normally be required (after having been done initially at the
factory), unless the source or detector has been changed. It requires two span gases, one fairly
low (e.g. 300 to 600 ppm), and the other near the high end of the desired operating range (e.g.
20000 ppm). The procedure is to perform a SPAN 1 command for the first gas (high or low),
and then a SPAN 2 command for the remaining gas.
Set Span 1
Readings are averaged for 30 seconds to compute
αα
1
1==−
W
W
Z
o
4-17
Equations 4-14 and 4-15 are performed, and the
T
value retained as a
T1
.
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