LumaSense Technologies INNOVA 1314i - Manual (Page 190)

Chapter 14
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BE6030-12 1314i Photoacoustic Gas Monitor LumaSense Technologies A/S
Page 190 of 199
If there is a perfectly linear relationship between the points C
low
, V
low
and C
high
, V
high
then:
V
lin
= ( C
h
/ C
l
) * V
l
GAS X: MEAS. INDICATES LINEAR COHERENCE
This message will be given in the status display if V
l
lies between the
values V
lin
– δ and V
lin
+ δ. This indicates that the two gas
concentrations you have chosen lie in the linear region of the
calibration curve. If the high concentration of gas you used (C
high
) is
equal to or greater than the highest concentration you expect to
measure, then it is not necessary to use a two-point span calibration,
a single-point span calibration using C
high
as the concentration of span
gas used will be sufficient to give you a good calibration result.
However, if the high concentration of gas you used is less than the
highest gas concentration you expect to measure, the two-point span
calibration task should be repeated using a high concentration which is
equal to or greater than the highest concentration you expect to
measure. There will therefore be a better chance to find a point in the
non-linear region of the span calibration curve so that any non-
linearity can be plotted.
GAS X: MEAS. DOES NOT FIT NON-LINEAR CURVE
This message will be given in the status display if V
l
is less than V
lin
–
δ. This message indicates that a two-point span calibration cannot be
performed.
If V
l
is found to be greater than V
lin
+ δ then the Monitor will try to fit
the two measured points onto a curve, whose shape has been pre-
determined by LumaSense, by an iterative process. The iterative
process involves scaling on the concentration and signal axes until the
two points fit the curve within certain tolerances.
GAS X: CALIBRATION IMPOSSIBLE: MAX ITER.
If after 255 iterative processes, the two points cannot be fitted onto
the curve within tolerance limits, this message is displayed.
This could indicate that the wrong concentration has been “entered” in
the set-up of the span calibration task (which does not relate to the
measured signal). Alternatively, it could indicate that there is a linear
relationship between the gas signal in the cell and the concentration of
the gas (in which case only a single-point span calibration is required).