Manual

Chapter 12
______________________________________________________________________
_____________________________________________________________________________
BE6030-13 1314i Photoacoustic Gas Monitor LumaSense Technologies A/S
Page 176 of 199
12.10.4 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 each of the installed filters (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 filters
“A” – “E”) 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.
12.11 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 each
of the filter banks 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 each of the filter banks 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.