Selecting FT4X Gases and Gas Mixes
Modbus register 40057 selects the gas type, which may be a pure gas (plus NAESB natural
gas composition), custom gas mix, or custom oil & gas mix. Register 40057 will read zero,
and register 40056 will read the gas selection that was chosen. Writing to register 40056 will
produce an error response. See the Gas Selection Codes table for the values to write.
Table 5.4: Gas Selection Codes
Selection Code
Gas
0
Methane
1
CO2 (Carbon Dioxide)
2
Nitrogen
3
Helium
4
Argon
5
Hydrogen
6
Air
7
Propane
8
n-Butane
9
Reserved
10
Oxygen
11
Ethane
12
Iso Butane
13
Pentane
14
Hexane
15
Heptane
16
Octane
17
Nonanes
250
Mixed gas (must set percentages)
251
Oil & Gas mix
Setting Mix Percentages
When a custom mix type is selected, the percentages of each gas in the mix must be set. These
percentages are 32-bit floating point numbers. Each constituent gas has a pair of registers to
hold its percentage.
Table 5.5: FT4X Modbus Holding Registers for Gas-SelectX®
40056
16-bit int
Gas type selection
See table of gas selection codes for
Modbus
40057
16-bit int
Gas type selection
40058
32-bit float LSW
Methane (C1) percentage
Percent (31.4 = 31.4%)
40059
32-bit float MSW
40060
32-bit float LSW
Carbon Dioxide percentage
Percent (31.4 = 31.4%)
40061
32-bit float MSW
40062
32-bit float LSW
Nitrogen percentage
Percent (31.4 = 31.4%)
40063
32-bit float MSW
90
Model FT4X
COMMUNICA
TIONS
Model FT4X
COMMUNICA
TIONS
Communications: Modbus