LumaSense Technologies 3434i SF6 Leak Detector - Manual (Page 173)

Chapter 12
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BE6028-14 3434i SF6 Leak Detector LumaSense Technologies A/S
Page 173 of 191
12.9.4 Performing a Span Calibration of the Water-vapour
Filter
Section 12.4.1 describes a good method of producing water-vapour
of known concentration. The directions for performing a span
calibration of water-vapour filter are similar to those for performing a
humidity-interference calibration of the other installed filters is as
described in section 12.7.2 . In both calibration tasks the signal in the
cell is measured when a supply of zero gas containing a constant
concentration of water vapour is attached to the Monitor. There are,
however, two differences:
1. During a humidity-interference calibration the signal is measured
using the installed filter (including the water-vapour filter),
whereas during the span calibration of the water-vapour filter the
signal is only measured with the water-vapour filter.
2. During a humidity-interference calibration, it is not necessary to
know the concentration of water-vapour supplied to the cell as it
is only necessary to measure the size of each signal (with filter
“A”) relative to the size of the signal measured with the water-
vapour filter. However, during a span calibration of the water-
vapour filter it is necessary to know the exact concentration of
water-vapour supplied to the cell, because during this calibration
the conversion factor is calculated. This factor relates the
measured signal to the concentration of water-vapour in the cell.
Follow the procedure described in section 12.7.2 .
12.10 Setting-up a Combined Zero-point and
Humidity-interference Calibration – Stand-
alone Use
We have explained in previous sections of this chapter ( section 12.6
and section 12.7.1 ) that a zero-point calibration can only be
performed alone if a humidity gain factor is already stored in the
filter bank which are active during the zero-point calibration task.
Likewise, a humidity-interference calibration can only be performed
alone if a concentration offset factor is already stored in the filter
bank which is active during the humidity-interference calibration
task.
If the necessary calibration factors are not stored in the Monitor’s
memory, a zero-point calibration task has to be performed together
with a humidity-interference calibration task.