Siemens SITRANS LUT400, Operating Instructions Manual

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A5E33329501 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS Page 267
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Flow Calculation
Special emphasis has been placed on providing the most accurate flow calculations possible.
To this end, specific routines have been written to comply with the British Standards Institute’s
Specifications BS-3680. These routines calculate correction factors taking into account
second order effects such as approach velocity and boundary layer.
If the PMD does not match any of the eleven preset PMD calculations, or if a PMD is not
used, select a Universal flow calculation (PMD = Universal Head Flow). Use the head/
flow graph or chart provided by the PMD fabricator (or create one based on the PMD or
channel dimensions).
The SITRANS LUT400 supports Universal curved flow calculation. This calculation
creates a cubic spline approximation of the head/flow curve, providing best results if the
curve is non-linear, and there are no sharp angles.
Select the head versus flow breakpoints to be entered (32 max). Generally, the more
breakpoints entered, the greater the flow calculation accuracy.
Select at least enough breakpoints from the curve to satisfy the following:
• two breakpoints very near the minimum head
• one breakpoint at the tangent points of each arc
• one breakpoint at each arc apex
• two breakpoints very near the maximum head
For combination curves, enter at least 2 breakpoints immediately before and after any
sharp angle (as well as 1 breakpoint exactly at the angle) on the curve.