MSA Senscient ELDS 1000 series, Operating Manual

Page: 155 / 184

Appendix C – Functional Testing Using Gas
Senscient ELDS™
Rev 15 155
GB
Example:
For a Cross Duct ELDS system installed across a 2.0metre wide duct, with a 0-25%LFL
measurement range, and for 100%LFL = 5%V/V methane:
Cross Duct Gas Challenge Cell ≈ 10,000ppm.m (8,000ppm.m – 12,000ppm.m)
%LFL =
10,000 x 100
(50,000) x 2.0
%LFL = 10.0%LFL
For a 0-25%LFL measurement range, the current output for 10.0%LFL on the 4-20mA output
should be:
I
4-20
= 4mA +
10.0 x 16
= 10.4mA
25.0
CAUTION
The significant difficulties and errors associated with in-field gas testing of open path gas
detectors (including cross duct types) result in large test error margins (≈±30%) that may lead to
unwarranted concerns about detector calibration. When testing the response of ELDS gas
detectors in field-service conditions, any unexpected results are far more likely to be due to test
errors, rather than a problem with an ELDS unit’s calibration. This is why most OPGD
manufacturers (including Senscient) do not allow in-field gas calibration of this type of gas
detector; and recommend that gas response checks only be treated as ‘bump-tests’ not
calibration verification checks.
Cross Duct ELDS systems can be supplied with 4-20mA outputs scaled for 0-10%LFL, 0-25%LFL
and 0-100%LFL. For all available measurement scales, 0%LFL will be signalled as a current of
4mA. Readings between 0% and 100% of the measurement scale will be signalled by a
proportional current between 4mA and 20mA.
In order to use the Refillable Cross Duct Gas Test Cell, the Gas Test Cell Aperture needs to be
uncovered. The Gas Test Cell Aperture can be uncovered by removing the two M5 bolts which
secure the aperture cover and removing the cover from the aperture.