INFICON Extrima Ex-certified Hydrogen Leak Detector - Manual (Page 11)

11
EN
INFICON - Operating Instructions EXTRIMA
Background compensation
There is always some hydrogen gas in the
background. In fresh air this is as low as
0.5 ppm (parts per million).
Extrima actively adjusts itself to the
background. This is done automatically
at start-up and thereafter it slowly adapts
itself to slow variations in the background
concentration. By adjusting slowly (mi-
nutes) it avoids taking an actual leak for
an increased background, and vice versa.
Therefore a sudden rise in background
concentration will be detected, but if the
concentration remains constant it will be
gradually cancelled out over a period of
several minutes.
For example, if the background concen-
tration, for some reason, should suddenly
rise to 10 ppm H
2
, then the detector will
give a corresponding signal which will,
very slowly, decline to zero. If you there-
after expose the probe to a leak which
gives rise to another 10 ppm H
2
, the
detector will give essentially the same
signal as if there was no background
concentration.
Interferences
Some examples of hydrogen sources
which could cause interferences:
- Engine exhaust
- Battery charging stations
- Welding smoke
- Cigarette smoke
- Breathing air
- Human flatulence
- Scratching on aluminium
Extrima is extremely selective. Among
naturally occurring gases only Hydro-
gen Sulphide (extremely toxic) gives a
comparable response to hydrogen. The
detector will also react to some synthetic
gases, predominantly used within the
semiconductor industry, such as Silane,
Phosphine, Arsine etc. Exposure to such
synthetic gases severely reduces the life
of the Hydrogen sensor.