Problem Solving
Senscient ELDS™
Rev 15
119
GB
The ELDS OPGD is Signalling Beam Block
After a predefined (configurable) time without receiving any signal from the ELDS Transmitter
opposite, an ELDS Receiver will signal a Beam Block condition (2.5mA) on its 4-20mA output.
There are a number of reasons why an open path gas detector might signal a Beam Block,
which include loss of power to the Transmitter, a vehicle, person or object blocking the
beampath, scaffolding erected in the beam, very dense fog, units being knocked out of
alignment, vegetation growing up, into and blocking the beampath; and the development of a
hardware fault. With there being numerous possible reasons for an OPGD to signal Beam
Block, it is imperative that when such a signal is received from an ELDS OPGD, a suitably
trained technician visits the detector in order to try to ascertain the root cause. For ELDS
OPGDs, the majority of Beam Blocks signalled do not reflect the fact that there is a problem
with the ELDS unit, but instead reflect a problem with the conditions that the unit is operating
under. When these conditions are addressed, the majority of Beam Blocks signalled will go
away.
Specifying the Most Sensitive Measurement Range for Toxic Gases
Based upon bad experiences where electrochemical and semiconductor toxic, point gas
detectors fail to detect leaks as expected, some ELDS users have specified and ordered the
most sensitive range of ELDS OPGD available for their particular toxic gas - with the objective
of increasing the probability of detection.
However, field service experience has established that using the most sensitive range available
can be a mistake. By virtue of being open path toxic gas detectors, ELDS OPGDs will detect
and integrate any and all of the target toxic gas that is present in their beam-path, even if this is
at very low, non-hazardous levels. The consequence of using the lowest available ELDS
measurement range and a correspondingly low alarm threshold can be that small, non-
hazardous background levels of toxic gases; or fugitive emissions, can result in alarm signals
being raised and operators becoming concerned. When this happens, users and operators
eventually establish that these alarms are a nuisance; and that the measurement range that
they have specified and the alarm thresholds that they have set are too low for their site and
application. As a consequence of this, the commonest service visit performed by Senscient
engineers (or our suitably trained selling and service partners) is to re-range ELDS OPGDs to
have a higher measurement range that is more appropriate to the application. In many
instances, this problem can be avoided by making use of the guidance on measurement
ranges and alarm thresholds provided in Appendix G of this manual.
RS485 Communications Blown by Wiring Up to +24V Power
The ELDS RS485 communications circuitry is protected against surges and transients, but
cannot withstand being unintentionally, permanently connected to the +24V power feed that is
supposed to provide power to the unit. If the +24V power is connected to the RS485 circuitry by
mistake, this will blow the RS485 isolation IC and RS485 communications will be lost. The only
way of repairing this is by returning the unit to Senscient for a replacement PSU PCB. When
wiring up ELDS units, always double check that you have not transposed the power and RS485
connections; and thereby avoid damaging RS485 communications.
The Bluetooth Communications Link is Less Reliable or has Shorter Range than
Expected
There are a number of reasons why a wireless, Bluetooth communications link is not as reliable
as a direct, hard-wired connection. None of these reasons are a consequence of there being
something wrong with an ELDS OPGD - they are all consequences of the nature of wireless
communications and how Bluetooth works. There are certain things about Bluetooth that are
not common knowledge, which when known, understood and taken into account, can help to
further improve the success with which Bluetooth is used. This information is presented in
section 4.6.1 of this manual.
Summary of Contents for Senscient ELDS 1000 series
Page 58: ...Installation Commissioning 58 Senscient ELDS Rev 15 GB 2 x Mounting Brackets ...
Page 140: ...Certification 140 Senscient ELDS Rev 15 GB 9 1 2 Control Drawing CENELEC ATEX ...
Page 142: ...Certification 142 Senscient ELDS Rev 15 GB 9 1 4 Control Drawing CSA US Canada ...
Page 159: ...Appendix D Manufacturer s EC Declarations Senscient ELDS Rev 15 159 GB ...
Page 160: ...Appendix D Manufacturer s EC Declarations 160 Senscient ELDS Rev 15 GB ...
Page 184: ...For local MSA contacts please visit us at MSAsafety com Because every life has a purpose ...
