Filter
Top Products
8
IP2046/IM
Nov 2006
It is important to note that the bottom reference of the transmitter should be related to the centre of the
invert of the primary device, NOT the distance to the channel bottom directly below the transmitter.
3.1.3 In-tank effects
• Stirrers or agitators can cause a vortex. Always try to mount the transmitter off-centre of any vortex to
maximise the return echo.
As stirrer blades become uncovered they will create echoes as they pass through the ultrasonic beam.
The transmitter can be tuned to ignore these false echoes on site.
• In non-linear tanks with rounded or conical bottoms, always mount the transmitter off-centre. In some
cases, it may be desirable to install a perforated reflector plate on the tank bottom directly under the
transmitter centre line to ensure a satisfactory return echo.
• Avoid mounting the transmitter directly above any pumps as the transmitter will detect the pump
casing as the liquid falls away. If this is not possible, fine tuning on site may be required to ignore
echoes from the pump casings.
3.1.4 Open Channel Flow installations.
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, in this case 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.
In the United Kingdom, Mobrey Ltd offers a complete installation and commissioning service for
open channel flow measurement systems. For further information contact the sales office and/or refer to
Mobrey’s ‘The Guide’.
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 4 to 5 times Hmax for a thin plate weir or 3 to 4 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 transducer. A minimum distance of
0.46m is recommended.
Hmax
Hmax + 0.46m