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December 2014
8
Quick Start Guide
Open channel flow installations
Mount an ultrasonic transmitter over an area of clear liquid. Avoid mounting the
transmitter directly over any inlet stream.
Never suspend the transmitter by the cable.
The positioning is critical, and should be the correct distance upstream from the flow
structure as stated in the relevant standard for your country. For example, in the ISO
standards, the distance should be four to five times the maximum height of the water
(Hmax) for a thin plate weir, or three to four times Hmax for a flume. For optimum
accuracy, position the transmitter’s front face at a height equal to the sum of the
maximum flow depth plus the transmitter deadband of 12.2 in. (300 mm) plus an
extra 2 in. (50 mm).
It is important that the bottom reference of the transmitter should be related to the
datum of the primary measuring device (Figure 7).
When setting the bottom reference on a ‘V’- notch weir, it is important the true invert
is used (Figure 8 on page 9) and not the meniscus level.
Figure 6. Choosing the height position above a flow
A. Transmitter front face
B. Hmax
C. Transmitter bottom reference = Hmax + 12.2 in. (300 mm) + 2 in. (50 mm)
Figure 7. Bottom reference of a flume or weir
A. Transmitter bottom reference C. Approach channel
B. Primary element (e.g. flume, weir) invert D. Flow
A
B
C
A
D
C
B