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12.
Glossary
Term
Definition
Target gas
Specific gas to be detected and used to trigger alarms.
Detection range
or measuring
range
A range of target gas concentrations that can be displayed and
trigger alarms.
Service range
A range of target gas concentrations the detector is able to
indicate, which are usually outside the Detection Range and
used only as reference.
Zero adjustment
(zeroing)
To adjusting the zero point (or 20.9% for oxygen) in clean air.
Clean air: air free from target or interfering gases, and
composed of 20.9-21.0vol% oxygen in dry conditions.
Gas atmosphere: Air containing target or interfering gases.
Span adjustment
To adjust the indicated values by using span gas.
Explosion-proof
structure
Structure of an electrical apparatus to not become an ignition
source in a flammable atmosphere
Intrinsically safe
(IS) structure
Structure tested (e.g., spark test) to not become an ignition
source in a flammable atmosphere due to an electrical spark
or hot surface during normal operation and fault conditions.
Hazardous area
An area in which an explosive atmosphere is present, or may
be expected to be present, in quantities such as to require
special precautions for the construction, installation and use of
electrical apparatus.
Non-hazardous
area
An area in which an explosive atmosphere is not expected to
be present in quantities such as to require special precautions
for the construction, installation and use of electrical
apparatus.
%LEL
Concentrations of combustible gas given in terms of percent of
the lower explosion limit.
vol%
Gas concentrations given in terms of percent of cubic volume.
ppm
Gas concentrations given in terms of millionth part of cubic
volume.
LEL
Lower Explosive Limit. Lowest concentration (percentage) of a
gas or vapor in air capable of producing a flash fire, or
explosion in the presence of an ignition source like arc, flame
or heat.
