Operating Principle - Siemens LDS 6 Operating Instructions Manual

Technical information

2.3 Operating principle

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Figure 2-5
For installation in EEx-protected environments, the legislative regulations have to be complied
with, such as the spatial separation of intrinsically-safe from non-intrinsically-safe cables.
• Max. 700 m between central unit and measuring point
• Hybrid and sensor connection cables
– Multimode fiber-optic cable, provided with SMA connections for transmission of the
– Two-wire copper cable, in twisted pair version, for +24 V supply of the detector electronics
• Additionally for the hybrid cable:
– Single-mode fiber-optic cable, configured double-sided with E2000 connectors for
• Rugged cable sheath for mounting in open cable ducts or ductworks
• Sheath material: oil-resistant polyurethane
2.3 Operating principle
LDS 6 is a gas analyzer employing single-line molecular absorption spectroscopy. A diode laser
emits a beam of near-infrared light, which passes through the process gas and is detected by a
receiver unit. The wavelength of the laser diode output is tuned to a gas-specific absorption line.
The laser continuously scans this single absorption line with a very high spectral resolution.
The result is a fully resolved single molecular line which is analyzed in terms of absorption
strength and line shape. The influence of cross-sensitivities on the measurement is negligible,
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Twisted pair of wires
Multimode fiber
Singlemode fiber
Connections of the hybrid cable
measured signal
(+12 V in the case of EEx-suitable instruments)
transmission of laser light
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Operating Instructions, 01/2022, A5E00295894-10
LDS 6