12
Disturbance source: valve
Inlet
Outlet
L
40 D
L
10 D
Disturbance source: pump
Inlet
L
50 D
Table 2: Recommended distances from disturbance sources
3.4
Pipe preparation
•
Clean dirt and dust from around the area of the pipework where
the sensors are to be placed;
•
Remove loose paint and rust with a wire brush or file.
Firmly bonded paint does not necessarily need to be removed provided the
flowmeter diagnostics indicate sufficient signal strength.
3.5
Clamp-on sensor mounting configurations and
distance
The most common clamp-on sensor mounting configuration is the Reflection
Mode, sometimes known as V-Mode (see Illustration 3, sketch (1). Here, the
ultrasonic signal passes twice through the medium (2 signal passes). The
Reflection Mode is the most convenient mounting method as the transducer
separation distance can be measured easily and the sensors can be accu-
rately aligned. This method should be used whenever possible.
An alternative mounting configuration (Illustration 3, sketch (3)) is the Diag-
onal mode (Z-Mode). The signals travel only once through the pipe. This
method is often used for larger pipes where greater signal attenuation might
occur.
Further variation of the Reflection and the Diagonal Modes are possible by
altering the number of passes through the pipe. Any even number of passes
will require mounting the sensors on the same side of the pipe, while with an
odd number of passes, the sensors must be mounted on opposite sides of
the pipe. Commonly, for very small pipes, sensor mounting configurations
such as 4 passes (W-mode) or 3 passes (N-mode) are used (Illustration 3,
sketch (2)).
Reflection Mode
Diagonal Mode