Siemens FUG1010 IP65 NEMA 4X, Operating Instructions Manual, Page: 96 / 271

Functions
7.1 Gas Parameters Menu
FUG1010 IP65 NEMA 4X
Operating Instructions, 01/2013, A5E02951519-AC
95
Spec. Heat Ratio
The specific heat ratio refers to the ratio of the gas specific heat at constant pressure to
specific heat at constant volume. This ratio (along with the measured gas temperature and
sonic velocity) allows the flow meter to compute (dynamically) the average specific gravity of
the gas. The default value of 1.3 is suitable for most gases, but should be modified if this
value is known for your specific application.
Viscosity (cP)
The absolute gas viscosity (along with the measured gas density and raw flow velocity) is
used by the flow meter to compute the instantaneous Reynolds number. The Reynolds
number is then used to derive the correction factor the required flow profile compensation.
The expected unit for viscosity is "centipoise." The default value of 0.01 is suitable for most
gases, but should be modified if this value is known for your specific application.
The Reynolds number is computed as indicated:
5
Q
F3
ˮ
[
LG
[
9
I
[
where: ρ = density at flowing conditions (g/cc)
id = spool inside dia (in)
Vf = Flow velocity (ips)
cP = absolute gas viscosity (centipoise)
Fixed MW g/mole
The flow meter uses the measured gas temperature, sonic velocity and specific heat ratio to
compute the average specific gravity of the gas being measured. This feature is useful for
identification of the gas as well as for proper reporting of mass flow in cases where the gas
composition varies.
In cases where the gas composition does not vary significantly, a fixed value for molecular
weight can be entered here. A non-zero value for Fixed MW (grams/mole) will override the
automatic computation of specific gravity. Setting Fixed MW back to 0.0 will cause the
automatic specific gravity computation to resume.
Estimated Vs
The [Estimated Vs] menu cell allows the numerical entry for the nominal sound velocity of
natural gas. Contact your local representative for gases other than natural gas.
Note
Changing the Estimated Vs will require repeating the Transducer Install procedure.