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Flow Appendix F
YSI Incorporated Environmental Monitoring Systems Operations Manual F-1
APPENDIX F FLOW
Flow is only available in the Sensors menu on sondes that have vented level. The Flow Setup menu only
appears when Flow is enabled in the Sensors menu.
Note: In this manual we describe how to use YSI’s sondes to calculate flow from vented level. While
weirs, flumes and the Manning equation are described briefly here, this manual is not a complete treatment
of the subject. We make no claims on the accuracy or appropriateness of any of these techniques for any
particular application.
Flow is a calculated value. Whenever there is a one to one relationship between the level of water in an
open channel and the flow of water through it, then flow can be calculated from a level measurement.
Many devices are designed to be placed in an open channel to improve the determination of flow. For
example, a weir is a dam of specific geometry that restricts the flow of water while giving a very repeatable
and accurate relationship between level and flow. There are several varieties of weirs, each designed for a
specific application. Similarly, a flume also restricts flow producing a repeatable and accurate flow/level
curve by forcing the flow not over a dam, but through a narrower portion of the channel. The flow is
gradually narrowed, passed through a throat in the flume, and then gradually expanded back to the original
channel width. As with weirs, there are several varieties of flumes each designed for a specific application.
The weir or flume is referred to as the primary measuring device, and the level meter is referred to as the
secondary measurement device. There are three common types of weirs and seven types of flumes. Most
of these are available in a number of sizes. Flow/level curves for common types and sizes are already
programmed in the sonde so that it is only necessary to describe the primary measuring device to get flow
readings. If you have a primary measuring device that is not already programmed, you have the option of
entering either an equation or a table that defines the flow/level curve for your device. The table can also
be used to calculate the flow of water in stream for which the flow/level data is available.
The Manning Equation is also available to calculate flow in an open channel without any restriction built
explicitly for measuring flow. In this case the channel itself is the primary measuring device.
SETTING UP YOUR SONDE
WEIR OR FLUME
Getting your sonde ready to calculate flow for a weir or a flume can be summarized in the following simple
steps. Using EcoWatch or a 650 MDS display/logger to communicate with the sonde:
1.
Enable Flow in the Sensors menu.
2. Go to Flow Setup menu in the Advanced | Sensor menu .
3. Choose a method (flume or weir), then a type (V-notch, rectangular, Parshall, etc.).
4. Choose a size.
5. Verify proper setup, choosing preferred units.
6. Choose preferred units in the Report menu.
The
Flow Setup menu only appears when Flow is enabled in the Sensors menu. Once in the Flow Setup
menu you must define your primary measuring device by Method, Type , and Size . Note that the menus
change depending upon your selection.
For example, after choosing
Flume for your method, only types of flume are shown. So it is important to
choose first the method, then the type, and finally the size. The following chart lists the primary devices
that are programmed in the sonde.