Rosemount 3491, Reference Manual, Page: 63 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
4-31
Rosemount 3490 Series
Table 4-9. Pre-programmed
flow calculation factors (Parshall
flumes)
Kindsvater Shen (V-notch)
P113 = “
Kindsvater Shen
”
The Kindsvater Shen calculation requires just the angle of the V-notch to
calculate a flow value over the weir. The head level is in units of metres and
the resultant flow value is in cubic metres per second (m
3
/s).
Exponential flow law
P113 = “
Flow calculation
”
Exponential laws are supported by selecting this profile option, and manually
entering values of k-factor, power, and mul.
The output is derived from the input value using:
Q = k x (mul x Input)
pwr
Using the 20-point manual (DIY) plot feature in a flow application
When parameter P113 is set to "Special", parameter P115 is used for defining
a 20-point look-up table that represents the flow profile of the channel. The
flow profile is established by entering the flow/liquid height relationship as a
series of Cartesian co-ordinates.
As an example, a 3/2 flume is shown in Figure 4-23.
The X points are at user-defined intervals, typically in equal (5%) increments
of height. However, this may be changed if it is required to concentrate points
at a particular level in the channel of flow structure. The Y points are the
corresponding flow rates.
Enter data in normalised form or in actual level/flow units.
For further details of programming the points, refer to page 4-26.
Profile P113
(1)
(1) After selecting a Parshall flume using P113, parameter P115 (Pwr, k, and mul factors) and parameter
P116 are populated for measuring flow in imperial units of US gallons per minute (GPM).
For flow measurement in alternative units (with automatic scaling of MCU PV), use the Duty Wizard.
(Menu: SETUP / [CONTROL UNIT /] DUTY(Mode) / Duty Wizard)
The choice of units offered depends on whether the transmitter is measuring in metric or imperial units.
Pwr (P115) k (P115) mul (P115) P116
Parshall 1 in 1.550 151.7 1.0 1.0
Parshall 2 in 1.550 303.4 1.0 1.0
Parshall 3 in 1.547 445.2 1.0 1.0
Parshall 6 in 1.580 924.5 1.0 1.0
Parshall 9 in 1.530 1378 1.0 1.0
Parshall 1 ft 1.522 1795 1.0 1.0
Parshall 1.5 ft 1.538 2693 1.0 1.0
Parshall 2 ft 1.550 3590 1.0 1.0
Parshall 3 ft 1.566 5386 1.0 1.0
Parshall 4 ft 1.578 7181 1.0 1.0
Parshall 5 ft 1.587 8976 1.0 1.0
Parshall 6 ft 1.595 10770 1.0 1.0
Parshall 8 ft 1.607 14360 1.0 1.0
Parshall 10 ft 1.600 17672 1.0 1.0
Parshall 12 ft 1.600 20982 1.0 1.0