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Reference Manual
IP2030/RM, Rev AA
Section 4: Getting started
June 2014
Section 4: Getting started58
4.5.14 Set-up open channel flow calculations for pre-programmed
flat, parabolic, and Parshall flumes (advanced users)
The MCU900 Series control unit has a library of data to set-up open channel flow calculations
with flat, parabolic, and Parshall flumes.
Essential parameters to program
Note
Flow calculations require the transmitter input channel(s) to be providing continuous
level measurements (see page 43). 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 metres per
hour (m
3
/hour) where flow Q is given by:
Q = k x (h x 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 metres 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.
Note
This modified version of the standard “Q=k x 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 4-1 on page 60 and Table 4-2 on page 60. Depending on the
derivation of k and the level units, the h value is scaled by a different mul factor.
Experienced users may wish to manually enter the values of k, mul or Pwr for specific
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.
When a flume is selected from this list, the MCU900 Series control unit also populates
parameters P400 and P401 (Current Output span), P530 (Totalizer factor), and
P531 (Totalizer units of m
3
or galx100).