Global Water FP101, FP201 User Guide

The Leader in Water Instrumentation

Level • Flow • Samplers • Water Quality • Weather • Remote Monitoring • Control

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User’s Manual

Global Water

Visit Our Complete Online Catalog www.globalw.com • Call [phone], 7:30 AM to 4 PM Pacific Time

International: US [phone] • FAX: [phone] • E-mail: [e-mail]

11257 Coloma Road, Gold River CA 95670 USA

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General Instructions 1

Average Velocity 2

Computer Operation 3

Computer Set-Up 4

Maintenance 5

Calculations 6

Extensions 7

Graphic Overview 8

Troubleshooting 9

Global Water Warranty 10

FP101/FP201 - 1

Global Water Instrumentation, Inc.

www.globalw.com • [phone] • US [phone] • FAX: [phone] • E-mail: [e-mail]

Congratulations on your purchase of a Global FP101 or FP201 Flow Probe!

Our Flow Probe has been field-tested in several hundreds of locations throughout the world. Our customers
praise the product’s ease-of-use, accuracy, durability, portability, and reasonable cost. Please follow the sim­ple procedures for operation presented in this manual and you will be accurately and reliably monitoring real­time flow in no time.

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1) Make sure the Flow Probe’s propeller turns freely by blowing strongly on the prop.

2) Point the propeller directly into the flow you wish to measure. Face the arrow inside the prop housing
downstream. The FP101 probe handle is a two piece rod expandable from 3’ to 6’, and the FP201 is a
three section rod expandable from 5’ to 15’. To expand the rod for correct placement in flow, loosen the
locking nut on the handle, pulling out the top piece and retightening the nut.

3) Scroll with the right button until the “V” for velocity appears on the left hand of the screen. The top num­ber in “V” mode is the instantaneous velocity to the nearest 0.1 ft/sec. Push the left button to toggle the
bottom number between maximum (“mx”) and average (“av”) velocities to the nearest 0.01 ft/sec.

4) With the propeller placed at your measuring point, push both the right and left buttons simultaneously and
release to clear the computer and reset the average and maximum velocities. Hold the probe in place for
several seconds until the average velocity reading steadies and then remove the probe. The average
velocity will freeze once the propeller stops turning. See Average Velocity section for more information on
obtaining average velocities.

5) Measure/calculate the cross-sectional area of your flow stream in square feet. If you are measuring flow in
round pipes, measure the depth of water and use the enclosed tables to determine cross-sectional area
(see Calculations section). If you are measuring flow in another channel type, manually measure water
depth at several points across the flow. These measurements are most easily recorded by drawing a dia­gram on graph paper with a scale of 1 square foot per graph paper square. Cross-sectional area (in
square feet) can then be found by counting the number of squares in the stream.

6) The average velocity (calculated with the Flow Probe in feet/second) times the cross-sectional area
(square feet) equals flow in cubic feet per second (cfs), or Q = V x A.

7) If the propeller gets fouled while measuring flow, clean it until the prop turns freely and start over.

FP101/FP201 - 2

Global Water Instrumentation, Inc.

www.globalw.com • [phone] • US [phone] • FAX: [phone] • E-mail: [e-mail]

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The Flow Probe is used to measure the average water velocity. Streamflow velocity varies for two reasons:

1) The velocities vary throughout the flow’s cross-section. In general, the velocities are greater in the center
of the flow and less near the bottom and sides of the channel.

2) The water surges in velocity with time. In a smooth running stream, the velocity at a specific point can
easily vary 1-2 feet per second over the period of a minute. This pulsating or surging of flow should be
averaged to obtain an accurate average flow reading (leave the probe in the flow through a series of flow
surges).

The Flow Probe can be used in three ways to determine average velocity in a stream.

1) For small streams and pipes, the probe can be moved slowly and smoothly throughout the flow during
average velocity measurement. Move the probe smoothly and evenly back and forth from top to bottom of
the flow so that the probe stays at each point in the flow for approximately the same amount of time.
Keep moving the probe for 20-40 seconds to obtain an accurate average value that accounts for surging.
(Move the probe as if you were spray painting and attempting to get an even coat of paint over the entire
surface.)

The Flow Probe uses true velocity averaging. When the average and maximum velocities are zeroed by
pushing both buttons, a running average is started. As long as the probe remains in the flow, the averag­ing continues. One reading is taken per second, and a continuous average is displayed. For example,
after 10 seconds, 10 readings are totaled and then divided by 10 and this average is displayed. Once the
average reading becomes steady, the true average velocity of the stream is obtained. When you pull the
probe from the water, this average value is frozen on the display until it is reset.

2) For larger streams and rivers where the Flow Probe can’t easily be moved throughout the flow, divide the
stream into subsections 2-3 feet wide. We recommend dividing subsections on your graph paper diagram
of the flow profile. Run a measuring tape across the stream for reference. Obtain a vertical flow profile at
the center of each subsection: zero the averaging function and move the Flow Probe vertically from the
surface to the bottom, up and down, slowly and smoothly for 20-40 seconds to obtain a good average.
The average velocity (obtained with the Flow Probe) times the area of the subsection (use your graph
paper diagram) equals the flow for the subsection (Q=VxA). Once the flow of each subsection is obtained,
add all of the subsection flows to obtain the Total Streamflow.

3) For the USGS “6 tens method”, the Flow Probe is placed at the center of the subsection at a depth from
the surface of 0.6 of the total depth. The Flow Probe is held in place and the average velocity is obtained
over a period of 40 seconds. The 0.6 depth is assumed to be the average velocity point for the vertical
profile. Therefore, this average is similar to that obtained in technique 2 (above), however, we feel that
technique 2 is more accurate.