Global Flow Probe
User Manual
7 December 2009
Kirsten Singleton
December 7, 2009
1 Introduction
The Magic Wand can be used to determine the velocity of flow through a pipe.
Though relatively easy to use, this instrument should produce the same results as
more technical and costly equipment, theoretically.
2 Hardware Configuration
The instrument consists of PVC tubing, which comprises the body of the wand,
shown in Figure 1.
[PVC body]
Figure 1.
The head, shown in Figure 2, contains buttons, which are used to change the system
functions. The head is detachable, with the battery located inside.
[Head]
Figure 2.
In the foot of the instrument body is a rotating head, shown in Figure 3, which
measures flow by rotations per unit time.
[Rotational unit]
Figure 3.
3 Operating the Instrument
This section tells how to operate the instrument. The instrument is composed of the
three main parts described in the hardware configuration.
To begin, press Button A, as identified in Figure 2, to turn the wand on. Next, press
the right button until “V” for velocity appears. Press the left button to toggle between
maximum (“mx”) and average (“av”) velocity readouts. Once this selection is made,
the wand is ready for use. A stopwatch will be needed to measure time. Place the
wand footing in the water, holding it in place with the arrow on the bottom of the
probe pointing downstream. Push both the right and left buttons simultaneously and
release to rezero and start measurement readings. Upon release and rezeroing, begin
the timer. After 40 seconds, lift the wand from the water and record the number on
the display. Repeat twice in this location, recording the measurements each time.
Then move to the next location and repeat the above steps. By making multiple
measurements, analysts are better able to account for experimental errors.
4 Saving the Measurements
Measurements are not recorded in the wand memory and, therefore, must be manually
recorded. An example data recording sheet is shown in Figure 4.
[ ]
Figure 4. Example Data Recording Sheet
The measurements that are recorded need to be multiplied by the constant
0.40557653 for feet per second.
5 Computing Discharge
The use of spreadsheets to calculate discharge is based on the theory that the flow rate
through the channel, Qi, is equal to the velocity in the channel, vi, times the area of
the channel’s cross-section, Ai, at that point.
Qi = vi *Ai
(1)
For the East Lab experiments, the wand was used to measure velocities in the
overflow channel and the return pipe.
5.1 Overflow Channel
The overflow channel was located at the end of the channel and conducted water that
had spilled over the ditch block back to the reservoir. Three stations were used for
this type of channel, as shown in Figure 9.
[ ]
Figure 9. Overflow Channel
5.2 Return Pipe
The return pipe was used to conduct water, which had left the flume through the
outlet box, back to the main tank. This was a _____diameter circular pipe. In the
pipe, a depth rod should be used to measure the height of water in the pipe. Using the
depth and the values given in Table ___, one can find the flow in the pipe.
Table ___. Calculations for Flow in Partially Filled Pipes
[
]
6 Troubleshooting
I) Probe won’t turn on.
a. The most common problem experienced at the East Lab was that the probe
simply would not turn on. To solve this problem, remove the instrument
head, open the rear door, and replace the battery. To avoid this problem,
turn the probe off or put it into sleep mode when not in use.
6
Bibliography