Siemens SITRANS FUP1010, Руководство по эксплуатации, Страница: 17 / 208

Volume Correction Algorithm
The flowmeter provides Standard Volume output by inferentially determining the liquid API @
60
o
F (or the specified base temperature) and then applying the API standard (2540) algorithm
as outlined below. Before describing API algorithm the steps required to obtain bulk or actual
flow should be reviewed.
1. Based on the measured transit time difference (Δt), average transit time (T
N
) and pipe
dimensions, the RAW flow rate (FLOW
RAW
) and liquid sonic velocity (Vos) are computed.
2. Using the liquid temperature input and the optional user provided pressure input, the
measured Vos is then compensated to the value expected for base temperature and
pressure conditions (i.e. 15.5°C and 1 bara or 60°F 14.7 psia). This compensated Vos is
called LiquIdent.
LiquIdent = Vos + TempSlope * (t - base temp) + PresSlope * (p = base pressure)
where: t = measured temperature (
o
F)
TempSlope = change in liquid sonic velocity per
o
F (Linear for petroleum products.)
PresSlope = change in liquid sonic velocity per PSI (Linear for petroleum products.)
LiquIdent provides an output that identifies the liquid independent of the operating temperature
and pressure.
1. Through optimization the LiquIdent values (for a wide range of different liquids) can then
be associated with an API@60
o
F as well as Viscosity @ 60
o
F. This information can be
keyed into a lookup table within the flowmeter. This table then serves as a reference for
dynamically inferring the liquid properties as different liquid batches enter the flow
transducer. (The lookup function for this table will also interpolate and extrapolate for values
between and outside the table values.)
2. Based on FLOW
RAW
and the inferred Viscosity, the current Reynolds # is computed. The
Reynolds # value is used to correct the raw flow for non-plug flow profile. The compensated
actual flow rate is then computed (FLOW
BULK
).
3. The volume correction can now be computed using API standard 2540. Note: 60
o
F is used
for the base temperature value in the example below, but this can be altered within the
flowmeter menu.
a) ρ
60
= (141.5 *999.012) / (131.5 + API60)where:ρ
60
= density at 60
o
F (Kg/m
3
)
b) α
60
= K
O
/ ρ
60
2
+ K
1
/ ρ
60
where K
0
and K
1
are coefficients of thermal expansion.
c) ρ
t
=ρ
60
* EXP (- α
60
Δt (1 + 0.8 α
60
Δt))where Δt = (t - 60)
o
F and t = measured temperature
d) Therefore the volume correction factor (VCF) = ρ
t
/ ρ
60
The final volume compensated flow rate is then: Std Flow = FLOW
BULK
* VCF
Flowmeter Types
The flowmeter automatically conditions Installation Menu choices to suit the selected meter
type. The following illustrates the 2-Channel and 2-Path flowmeter types.
Description
3.3 Theory of Operation
FUP1010 IP67 Portable Flowmeter
Operating Instructions, 02/2010, A5E02951522A Revision 01 15