Emerson Micro Motion SGM Series - Page 42

Example: Calculating the control pressure for natural gas
Control pressure and measurement error calculations for natural gasTable 5-2:
Gas Natural gas
Specific gravity range 0.55 to 0.8
DTC (kg/m³/°C) −0.0003
Control pressure at 20 °C lb/in² absolute 18 30 60 100
Bar absolute 1.2 2 4 7
Density range at 20 °C kg/m³ 0.79 to 1.15 1.32 to 1.92 2.64 to 3.84 4.62 to 6.72
Measurement error (% of
full-scale
specific gravity/°C )
Temperature coefficient −0.026 −0.016 −0.008 −0.004
Gas compressibility of sam-
ple gas
±0.0003 ±0.0003 ±0.001 ±0.002
Velocity of sound in sample
gas
−0.003 −0.003 −0.003 −0.003
Reference chamber or relief
valve
0.007 0.007 0.007 0.007
Total error (%) −0.022 −0.012
−0.005 to
+0.003
−0.002 to
0.000
Example: Calculating the control pressure for an N
2
/CO
2
mix
Control pressure and measurement error calculations for an N
2
/CO
2
mixTable 5-3:
Gas N
2
/CO
2
mix
Specific gravity range 1.0 to 1.5
DTC (kg/m³/°C) −0.0003
Control pressure at 20 °C lb/in² absolute 18 30 60 100
Bar absolute 1.2 2 4 7
Density range at 20 °C kg/m³ 1.44 to 2.16 2.4 to 3.6 4.8 to 7.2 8.4 to 12.6
Measurement error (% of
full-scale
specific gravity/°C )
Temperature coefficient −0.014 −0.008 −0.004 −0.002
Gas compressibility of sam-
ple gas
±0.002 ±0.004 ±0.008 ±0.015
Velocity of sound in sample
gas
−0.005 −0.005 −0.005 −0.005
Reference chamber or relief
valve
0.007 0.007 0.007 0.007
Total error (%) −0.014 −0.006
−0.010 to
+0.006
−0.015 to
+0.015
Purging and calibration
34 Micro Motion
®
Gas Specific Gravity Meters (SGM)