4230 Flow Meter
Section 2 Programming
2-6
This method keeps program size manageable and makes pro-
gramming more efficient. By turning off unneeded features of the
program early, you do not have to keep de-selecting those fea-
tures over and over as you work through the program.
Consequently, you should choose carefully from the first step. We
suggest you study the program first, then fill out the Pro-
gramming Worksheets (in the back of the manual), and program
the flow meter last, if you are unfamiliar with the unit.
2.5.2 Flow Conversion Type Step 2, Flow Conversion Type, determines how the flow meter
calculates flow rate and total flow. For the 4230, flow rate is cal-
culated by knowing the measured level and (usually) the charac-
teristics of a structure called a primary measuring device.
A primary measuring device is a structure placed in a flow
stream through which the stream flows. These devices are made
in a number of styles and sizes, but they all have one thing in
common: For any type of primary measuring device there is a
known relationship between the level in the flow stream ahead of
the device and flow rate through the device. Consequently, after
you measure level with the flow meter, it can calculate flow rate
and total flow from the measured level, by consulting built-in
look-up tables.
Information about many common primary measuring devices is
provided in the Isco Open Channel Flow Measurement
Handbook. This useful book provides formulas, flow rates at
various levels, and values for maximum head, as well as much
interesting descriptive material. This book is available on
request from Isco. If your installation uses a nonstandard
primary device, you should consult the manufacturer of the
device for flow rates at given levels. The flow meter will then cal-
culate a flow conversion for such a device on the basis of the man-
ufacturers' data you enter as data points or an equation. In some
instances, a nonstandard primary device could be supplied with
a flow equation; you can enter that equation into the flow meter
and the flow meter will calculate the flow rate from that
equation.
Flow Calculations Without Primary Devices – However, it
is not always necessary to have a primary measuring device. The
4230 Flow Meter can measure level and calculate flow without
having any primary device installed in the flow stream. Some-
times the shape of the flow stream itself forms the primary
device.
The Manning formula uses the shape of a pipe or channel and
its slope to calculate flow in open (non-pressurized) pipes.
An accessory is available for the 4230 called the Flow Metering
Insert. These inserts, used in round pipes of 6", 8", 10", and 12",
form a primary device inside the pipe by restricting flow and
measuring the level of the liquid backed-up behind the insert.
The opening in the insert, either a smaller round opening or a
V-notch that forms a weir, forms a primary device.
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