MSA Senscient ELDS 1000 series, Operating Manual

Page: 143 / 184

Appendix A – Glossary
Senscient ELDS™
Rev 15 143
GB
10. Appendix A – Glossary
10.1. Terminology
Ex d
Flame proof or explosion-proof within the confines of European standards EN60079-0.1. An
enclosure that can withstand the pressure developed during the internal explosion of an explosive
mixture and that prevents transmission of the explosion to any explosive atmosphere surrounding
the enclosure.
Lower Flammable Limit (LFL)
The lowest concentration of a flammable gas or vapour in air which can be ignited.
RS485
An industry-wide serial communication link specification (physical layer / hardware).
Modbus
An industry-wide serial communication protocol (software layer).
HART
An industry-wide, FSK-based, digital signalling protocol providing bidirectional communications on
top of the analog signal on a 4-20mA loop.
10.2. Measurement Units
LFL.m
Lower Flammable Limit metres (LFL.m). Open path detectors measure the total amount of gas
present in the beam-path. LFL.m readings are calculated by multiplying the flammability (LFL) of
the gas in a gas cloud by the cloud’s size (m)
LFL.m monitoring can be particularly beneficial when ELDS™ gas detectors are protecting the
perimeter of a plant or process, by greatly reducing the number of detectors required and providing
the ability to detect gas at concentrations that are too low to be detected by point detectors.
ppm.m
Parts (by volume) per million metres. Open path detectors measure the total amount of gas
present in the beam-path; ppm.m readings are calculated by multiplying the concentration (ppm) of
the gas in a gas cloud by the cloud’s size (m). ppm.m units are typically used for toxic gases,
which generally need to be detected and/or measured at much lower concentrations than
flammable gases.