Model 4802A
45
6.3 System
Specifications
6.3.1 Application
Combustible & Flammable Gas and Vapor Detection.
6.3.2 Sensor Type
General Monitors Low Temperature, Diffusion Limited, Catalytic Bead Sensor.
6.3.3 Typical Sensor Life
4 to 5 years, in normal service.
6.3.4 Measuring Range
0 to 100% LEL.
6.3.5 Converting Test and Calibration Gas Concentrations for % LFL to % LEL
Using %LFL as described in
NFPA 325 Guide to Fire Hazard Properties of Flammable
Liquids, Gases, and Volatile Solids 1994 Edition
it is then used as 100% LEL fraction.
Example Hydrogen has a 4% LFL (Lower Flammable Limit) is then used as 100% LEL
fraction, so that when an environment that has 2% LFL (Lower Flammable Limit) would
indicate 50% LEL
6.3.6 Accuracy
The accuracy the 4802A is limited by the accuracy of the standard used to calibrate the
system. For many combustible gases, obtaining a high accuracy standard that is
suitable for field calibration use may be difficult (about the best accuracy of gas
concentration achievable is +/-5%, using a permeation system with good temperature
control). For this reason, no fixed accuracy statement is possible. The accuracy cannot
be better than the accuracy of the calibration gas.
The best accuracy to be expected, assuming a perfect standard, is ± 3% LEL up to 50%
LEL and ± 5% LEL > 51% LEL, at reference ambient conditions and when the unit has
been calibrated using 50% LEL.
6.3.7 Relative Sensitivities
Methane
100.0
Hydrogen
64.7
Ammonia
132.8
Butadiene
84.6
Butane
66.4
Ethane
86.2
Ethylene
87.1
Propane
77.6
NOTE:
The above are approximate values only
Beyond the standard gases the sensor is configured for, each gas sensor can be
configured to be gas specific. General Monitors, Inc. can conduct an evaluation study to
custom configure a gas sensor.
6.3.8 Zero Drift
Less than 5% of span, per year.
