C
12-17 Combustible Gas Transmitter
14
O&M Manual
Rev-D
CALIBRATION FOR OTHER COMBUSTIBLE GASES
As previously mentioned, a combustible gas sensor has a slightly different response to each
combustible gas or vapor. In addition, the LEL (Lower Explosive Limit) represents different percent
concentrations for different gases. For instance, the LEL for methane is 5% by volume while the LEL for
butane is 1.9% by volume. Because of these factors, a combustible transmitter must be adjusted
differently if the system is meant to detect a gas or vapor other than methane.
A 1% methane gas standard may still be used for calibration of combustible transmitters when
used for other gases. However, the voltage that you set at the transmitter test point will be different for
each gas. Table 1 provides the voltage setting for various gases, and the corresponding percent LEL
reading for each.
TABLE 1
GAS
VOLTAGE, mV
% LEL
Methane
72
20
Propane
98
36
n-Butane
96
35
n-Pentane
109
43
n-Hexane
127
56
Hydrogen
82
26
Methanol
77
23
Ethanol
83
27
Isopropyl Alcohol
109
43
Acetone
102
39
Methyl Ethyl Ketone
118
49
Benzene
120
50
Toluene
120
50
Acetylene
98
36
Di-ethyl Ether
109
43
Ammonia
67
16
n-Heptane
125
53
