Flow Profile Compensation; Standard Volume Compensation - Siemens SITRANS FUG1010 IP65 NEMA 4X Instruction Manual

Section 1

1.3.2 FLOW PROFILE COMPENSATION

Although gas has a very low absolute viscosity, its kinematic viscosity can be greater than water. The
FUG1010GCN flowmeter continually computes the kinematic viscosity (centistokes) by dividing the fixed
viscosity entry (from gas parameters menu) by the computed gas density (see paragraph 1.3.3). The
Reynolds number is then computed as follows:
Rn = 645 * Pipe ID * V
The flowmeter then uses this computation of Reynolds number to compensate the raw flow velocity for
conditions of laminar or turbulent flow profile as defined by an internal Reynolds compensation table.
The meter then converts the compensated flow velocity to volumetric flow rate.
Rate = V

1.3.3 STANDARD VOLUME COMPENSATION

Due to the high compressibility of gas, volumetric flow rate and total are commonly reported in stan-
dard volume (or normal) units. This requires the FUG1010GCN flowmeter to dynamically compensate
the actual measured volume to the volume anticipated at some specified reference pressure and tem-
perature (referred to as base press and base temp in the Gas Parameters menu).
To compute this volume correction the flowmeter requires the input of actual operating temperature and
pressure. With this information the flowmeter computes the standard flow rate as shown: Note: The
flowmeter allows for a fixed entry of the gas compressibility factor or provides dynamic AGA8 compen-
sation via an internal lookup table for standard volume compensation. If the gas composition varies
significantly then an AGA8 volume compensating flow computer must be used where very high volume
correction accuracy is required.
where: Q = Volumetic flow rate
1.3.4 MASS FLOW COMPUTATION AND SPECIFIC GRAVITY
The FUG1010GCN flowmeter includes two different methods for computing the actual density of the gas
being metered. The first method takes advantage of the transit-time measurement of the gas sound
velocity (VOS or Vs) along with the measured temperature and the input of the gas specific heat ratio to
determine the average specific gravity of the gas. This method is suitable for lower pressure applications
where the gas composition varies dramatically.
The second method requires the input of an AGA8 based volume compensation table, which contains
both the Z-factor and gas density for a specified range of pressure and temperature. This method is
suitable for any pressure and temperature as long as the gas composition does not vary significantly,
however a new table can be generated and installed to accommodate changes in gas composition. As
with the standard volume compensation, a flow computer and gas chromatograph should be used
where very high accuracy is required.
F
Viscosity
* Comp(Rn) * Pipe area
F
Std. Rate = Q
act
P = Pressure (absolute)
T = Temperature (absolute)
Z = Compressibility
base = Base conditions (pressure and temperature)
act = Actual flowing condition (pressure and temperature)
where viscosity = cS = cP/density
P T Z
act base base
˜ ˜ ˜
P T Z
base act act
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1010GCNFM-3C