Operating instructions

14 GMS810-/GMS811-FIDOR · Operating Instructions · 8013911 V1-0 · © SICK AG
Product Description
Subject to change without notice
2.2.3 Measuring principle
Fig. 2 Measuring principle
● The FIDOR uses a flame ionization detector (FID) for measuring the hydrocarbons.
● A hydrogen flame supplied by fuel gas and combustion air burns in the FID. The sample
gas is routed into this flame.
● The hydrocarbons contained in the sample gas are split; the produced hydrocarbon
fragments are ionized. A stream of ions forms in the electric field and this electrical
stream is measured.
● The measuring signal is proportional to the number of the listed, non-oxidized hydrocar-
bon atoms. Hydrocarbon atoms which are already oxidized are only partially detected.
CO and CO
2
are ineffective.
● The quantitative correlation between the measurement signal and the hydrocarbon
concentration in the sample gas is determined by performing reference measurements
with test gases which do not contain any hydrocarbons (zero gas) or of which the hydro-
carbon concentration is known exactly (reference gas – e.g. 80 ppm propane in air).
● Only a small portion of the sample gas is burnt for analysis, the major portion is diluted
with instrument air and combustion air and routed outside via the exhaust gas line.
Combustion air
(Instrument air)
Sample gas
Fuel gas