Emerson Rosemount 3490 Series, Reference Manual

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Set-up open channel flow calculations for pre-programmed
flat, parabolic, and Parshall flumes (advanced users)
The Rosemount 3490 Series Control Unit (“control unit”) has a library of data to set-up
open channel flow calculations with flat, parabolic, and Parshall flumes.
Related information
Optional change: transmitter input channel settings (advanced users)
Essential parameters to program
Note
Flow calculations require the transmitter input channel(s) to be providing continuous level
measurements. Also, P200 (control unit PV units) must be changed from the default % to
the required flow measurement units.
Select a flume
Use parameter P113 (or P123) to select a flume from the option list. The control unit then
automatically populates parameter P115 (or P125) with data from the built-in library.
The control unit uses P115 (or P125) in a different way to when a plotted profile is
required. For flat and parabolic flumes, it is used to store values for the flow calculation in
cubic meters per hour (m
3
/hour) where flow Q is given by:
Q = k × (h × mul)
Pwr
where h is the height of channel flow, and k and Pwr are factors.
When a flat or parabolic flume is selected, P115/P125 (Pwr, k, and mul factors) and P116/
P126 are populated for measuring flow in metric units of cubic meters per hour (m
3
/hour).
When a Parshall flume is selected, P115/P125 (Pwr, k, and mul factors) and P116/P126 are
populated for measuring flow in imperial units of US gallons per minute (GPM).
For flow measurement in alternative units, with automatic scaling of the control unit PV,
use the App Wizard (menu:
SETUP
→
[CONTROLLER]
→
APPLICATION
→
App Wizard ).
The choice of units offered depends on whether the transmitter is measuring in metric or
imperial units. When using the App Wizard, select Parshall or Vlarem at the prompt for a
profile, and the next prompt then allows selection of the pre-defined calculation e.g.
Flume Flat 1.
Note
This modified version of the standard “Q=k × h
Pwr
” flow formula allows the use of a
multiplier (mul) factor. This extra factor can account for irregularities or errors in the flow
structure, but should only be manually entered where errors can be quantified.
Pre-defined values for factors k, mul and Pwr of each standard flow structure in the library
are shown in
Table 4-2 and Table 4-3 . Depending on the derivation of k and the level units,
the h value is scaled by a different mul factor.
Experienced users can manually enter the values of k, mul or Pwr for applications. To edit
these, set P113/P123 to be “Flume***” and then edit k, mul or Pwr at parameter P115/
P125. Use the
down arrow button to display the mul value.
Getting started Reference Manual
January 2021 00809-0100-4841
78 Emerson.com/Rosemount