MSA Senscient ELDS 1000 series, Operating Manual

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Installation & Commissioning
Senscient ELDS™
Rev 15 95
GB
For dual laser units there is a further possible message. If the signal levels for each laser are very
different from each other then the following will be displayed:
There are two (2) possible reasons for this.

The transmitter is not well aligned to the receiver. Re-check the alignment of the
Transmitter using the alignment telescope and ensure that the alignment telescope has not
been damaged (be being dropped for example, the procedure to check the telescope is
described in section 4.3.2). This is the most likely reason for this warning.

The transmitter has a large imbalance of the laser signals. If the alignment is checked as
described above and no error is found and it is also confirmed that the alignment telescope is
correctly aligned then it may be that the transmitter has a larger than normal imbalance of
output power for the two lasers. Normally Senscient will only supply Transmitters that have a
well matched output powers, however because lasers have a range of properties and have to
be ‘selected’ for each application occasionally units may have a significant difference in the
signal level for each laser. SITE normally allows for such possible differences but occasionally
where a transmitter is near the limit of imbalance it may be that this message will occur.
Given that re-aligning the transmitter or receiver is unlikely to correct this problem when it is
caused by a ‘marginal’ transmitter SITE will allow the installation to proceed even though the
laser powers are badly matched. The system will function normally despite this imbalance.
5) Detector Zeroing (Where Applicable)
There are three (3) zeroing regimens for ELDS gas detectors:

Zeroing Essential.
For some ELDS units (specifically older and now discontinued types) it is
essential that the detector is zeroed as-installed and as-aligned. In such instances, SITE
enforces the requirement for detector zeroing.

Zeroing Advisory but Optional. For ELDS detectors such as 0-250ppm.m H
2
S, provided that
an H
2
S-free background is present, zeroing as-installed and as-aligned will achieve the best
detector zero. In such instances, SITE offers the user the option of zeroing the unit as installed
(advisory) or using the TX Factory Zero where background gas might be present in the path.

TX Factory Zero Known Best. For many of the gases and measurement ranges for which
ELDS gas detectors are available, the TX Factory Zero is known to be a much better zero than
can be obtained in field-service conditions. In such instances, SITE automatically uses the TX
Factory Zero and does not offer any other zeroing option.