MSA Senscient ELDS 1000 series, Operating Manual

Page: 150 / 184

Appendix C – Functional Testing Using Gas
150
Senscient ELDS™
Rev 15
GB
12.2.2 Procedure for Testing Gas Response Using Gassing Cell
The gassing cell is designed to fit onto the front of an ELDS™ Transmitter or Receiver unit. It may
be helpful to move the sun shield to the furthest back position to allow better access to the
clamping bolts on the cell when fitting the cell.
In common with all optical gas detectors the ELDS™ OPGD responds to the total quantity
of gas in the beam. When attempting to check gas response using a Gassing Cell, the
quantity of gas in the beam will be affected by atmospheric pressure and ambient
temperature. Suitable allowance for these factors must be made when assessing the gas
response of the detector. Errors of the order of ±15% of reading should be expected; whilst
errors as large as ±30% of reading may occur at times.
When testing the gas response of an OPGD, the very best results will be obtained when
the unit’s windows are clean, the alignment is good and the system has the best zero
possible.
Where high or unstable background levels of target gas are known to be present, the
factory zero will usually be the best zero available. However, in installations where there is
no target gas background or where this background is small and stable, zeroing the system
as-installed may further improve zero quality.