Emerson Rosemount 3100 Series, Справочное руководство, Страница: 23 / 144

Reference Manual
00809-0100-4840, Rev. BA
July 2008
3-7
Rosemount 3100 Series
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 instrumentation). For accurate open channel flow
measurement, both parts of the system must be installed accurately.
This manual explains some key aspects of the installation of the secondary
element, which, in this case, is the ultrasonic transmitter. For full details of the
installation of a primary element, such as a flume or weir, reference should be
made to the relevant British (BS3680) or International standard.
Positioning of the transmitter is critical and should be the correct distance
upstream from the flow structure as stated in BS3680 e.g. a distance of four to
five times Hmax for a thin plate weir, or three to four times Hmax for a flume.
For optimum accuracy, the front face of the transmitter should be positioned
at a height that is at least equal to the maximum flow depth plus the blanking
distance of the transmitter (see Figure 3-4).
A minimum distance of 12.2 in.
(0,31 m) from the flow is recommended.
Figure 3-4. Choosing the Height
Position Above a Flow
It is important to note that the bottom reference of the transmitter should be
related to the center of the invert of the primary device (see Figure 3-5), and
NOT the distance to the channel bottom directly below the transmitter.
Figure 3-5. Bottom Reference of
a Flow Channel
Hmax + 12.2 in.
Hmax
Transmitter front face
Flow
Channel invert
Primary device
(e.g. flume, weir) invert