Measurement Of Path Length - Siemens LDS 6 Operating Instructions Manual

Preparations for Installation
CD 6C – Water vapor sensor for LDS 6
A5E00912721-01
Figure 2.5 The error angle

2.1.4 Measurement of Path Length

It is recommended that the open end of the purging tubes are
the reference points from which the path length is determined.
When the flanges are permanently installed, measure the dis-
tance between the outside of the flanges (measurement A in Fig-
ure 2.4) with an accuracy of at least ±10 mm (±0.4"). This dis-
tance is used to calculate the path length (by subtracting the
length of the flanges from A) and will later be used in the ana-
lyzer when it calculates the gas concentration. In the area where
the purging gas and the measurement gas are mixed there will
be a zone of uncertainty. This zone will depend on the purging
flow and the flow of the measurement gas.This is further
described in Appendix B.
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