Siemens SITRANS FUS1020, Руководство пользователя, Страница: 19 / 251

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1020NFM-1D Section 1
The degree of the flow profile curvature is directly proportional to the Reynolds number of the flowing
liquid. FUS1020 software applies a compensation factor, which is selected based on knowledge of the
Reynolds number of the liquid. The algorithm continuously calculates this number from the measured
flow velocity, the pipe diameter and the viscosity of the liquid. The user enters this information during
the site setup procedure. The FUS1020 infers the current liquid viscosity and accommodate installa-
tions whose piping configuration does not permit fully developed flow, such as conditions where a
limited upstream straight pipe run is available for transducer installation.
Reflect mounting automatically corrects for non-axial flow or cross flow conditions. When the ex-
change of sonic signals occur by reflection off the far pipe wall as shown above, the average beam
versus stream angle will be equivalent to that of an axial flow stream.
Another important consideration is that the ultrasonic flowmeter has to compensate for the flow profile
to maintain calibration accuracy. Shown below is a graphic of a “fully-developed” flow profile. Note that
the fluid velocity increases toward the center (axis) of the flow stream.
Fluid velocity near the axis
of the flow stream tends to
be greater
Flow Calibration Factor
Normally, the flow stream is in line with the axis of the pipe. On this basis, the calibration factor of a
clamp-on ultrasonic flowmeter is proportional to the cosine of the beam angle relative to the pipe axis.
However, this reveals that if the angle of flow stream is
not in line with the pipe axis, the flow calibration
factor could be compromised. This most often occurs when the transducer mounting location is within
close proximity of a bend or other pipe obstruction. This is why we recommend that whenever possible
you mount clamp-on transducers on the longest available straight run of pipe and also use Reflect
Mode mounting (as shown below).