Terms And Units - Herth+Buss SelectH2 mini Bedienungsanleitung

Operating Instruction

3. Terms and units

ppm
Stands for parts per million = number of
parts per million of other parts, a customary
value for smallest quantities in gas detection.
Lower explosion limit LEL
At certain values in a mixture with air
(atmospheric oxygen), different depending
on the type of gas, combustible gases reach
a point at which the influence of an ignition
source results in an explosive ignition. This
is referred to as the lower explosion limit
(LEL, or sometimes lower flammable limit
"LFL ") and is 4.4 vol% for hydrogen. This
means that relatively small quantities are
enough to create a flammable mixture. The
100 % Gas
75 % Gas
4,4 % Gas
0 % Gas
23
Gas
Hazardous area
Luft
1 ppm is the quantity of 1 cm
of air. 1 ppm = 0.0001 vol %, so that 0.1 % gas
= 1,000 ppm.
following figure shows this using a room as
an example. Gradual filling with gas results
in the value of 4.4 % being reached quickly.
The range from 0 % gas to the LEL is divided
into % of the LEL. 4.4 % hydrogen in air
corresponds to 100 % of the LEL.
The SelectH mini uses acoustic signals
2
to indicate that this LEL value is being
approached.
0 % Air
UEL UEL... Upper explosion limit
LEL LEL... Lower explosion limit
100 % Air
95980019
EN
of gas in 1 m
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