Introduction
1. Introduction
The Senscient ELDS™ 1000 / 2000 Series is a range of open path, flammable and / or toxic gas
detectors that is currently available in the following versions.
Senscient ELDS™ Series 1000 CH
4
- Methane Detector
Senscient ELDS™ Series 1000 Ethylene, HF, HCl, NH
3
or CO
2
Detectors
Senscient ELDS™ Series 1000 XD – Cross Duct Methane Detector
Senscient ELDS™ Series 2000 H
2
S - Hydrogen Sulfide Detector
Senscient ELDS™ Series 2000 CH
4
+ H
2
S - Simultaneous Methane &
Hydrogen Sulfide Detector
The Senscient ELDS™ Series 1000 detector consists of a Transmitter unit that sends an infrared
laser beam to a separate Receiver unit that can be installed on a line-of-sight at a distance of up to
200m. The ELDS 1000 Series CH
4
detector can be located where there is a risk that a leak of
flammable methane gas may occur, to provide a rapid, early warning of such a hazard. The
ELDS™ 2000 variants are similar, except that there are two coinciding infrared laser beams, which
can either be used to detect two or more gases, or to detect a single, difficult gas with high
sensitivity (e.g. Hydrogen Sulfide).
All ELDS™ gas detectors operate on the principle of absorption of infrared laser light. Gases
absorb light at specific wavelengths depending on their molecular composition. Hydrocarbon
gases such as methane and propane absorb in the infrared region of the spectrum. If a cloud of
target gas is present, the specific wavelengths of the infrared laser light output by the ELDS™
Transmitter are absorbed by the gas, introducing Harmonic Fingerprints onto the signals reaching
the Receiver that are proportional to the amount of gas in the beam.
The Senscient ELDS™ Transmitter unit produces the precisely controlled infrared laser light
required to detect the target gases; whilst the Receiver unit contains an infrared detector and
advanced signal processing electronics which look for the Harmonic Fingerprint produced by the
presence of target gas in the beam-path. Each unit is housed in a robust 316L stainless steel
housing. The Receiver features two 4 - 20mA analogue outputs which are used to signal the
quantity of each target gas measured in the beam-path, for example 0-1LFL.m CH
4
and
0-250ppm.m H
2
S for the Series 2000 detector. These outputs provide a linear relationship with the
measured gas burden.
Note that open path detectors do not measure the point concentration of the target gas(es), rather
they measure the integrated concentration over the length of the measurement path between the
Transmitter and Receiver units. This means that the probable size of a gas cloud must be
considered when estimating the concentration of gas that might be present, with alarm levels
being set accordingly. The figures on the following page illustrate this.