Emerson Rosemount 3101 Quick Start Manual page 12

Quick Start Guide
6.3 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.
Positioning of the transmitter 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, the transmitter's front face should be
positioned at a height equal to the sum of the maximum flow depth plus the
transmitter dead band of 12.2 in. (300 mm) plus an extra 2 in. (50 mm).
Figure 8. 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)
It is important that the bottom reference of the transmitter should be related to
the datum of the primary measuring device
Figure 9. Bottom Reference of a Flume or Weir
D
C
A. Transmitter bottom reference
B. Primary device (e.g. flume, weir) Invert D. Flow direction
12
A
C
B
(Figure
A
B
C. Approach channel
September 2018
9).