Emerson Rosemount 3101, Reference Manual

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14
Reference Manual
00809-0100-4840, Rev CB
Section 3: Installation
February 2015
Installation
3.3.5 Open channel flow installations (the 3102/3105)
There are normally two distinct parts to an open channel flow measurement system; the
primary element (flow structure) and the secondary element (Head measurement instru-
mentation). For accurate open channel flow measurement, both parts of the system must be
correctly installed. This section explains the important parts of installing the transmitter
(secondary element). The flow structure (primary element) installation can be referenced in the
British (BS3680) or ISO International standards.
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, 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).
Figure 3-5. 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 (see Figure 3-6 ).
Figure 3-6. Transmitter Bottom Reference for a Flume or Weir
A. Transmitter Bottom Reference C. Approach Channel
B. Primary Element (e.g. Flume, Weir) Invert D. Flow
A
B
C
D
A
B
C