Dwyer Series PUB - Manual (Page 11)

2: Installation
7
2: Installation
2.1 Transducer Positioning
Figure 2.1 Locating the transducers
To obtain the most accurate results, the condition of both the liquid and the pipe wall must be suitable to allow the
ultrasound transmission along its predetermined path. It is important also that the liquid flows uniformly within the
length of pipe being monitored and that the flow profile is not distorted by any upstream or downstream
obstructions. This is best achieved by ensuring there is a straight length of pipe upstream of the transducers of at
least 20 times the pipe diameter and 10 times the pipe diameter on the downstream side, as shown in Figure 2.1.
Flow measurements can be made on shorter lengths of straight pipe, down to 10 diameters upstream and 5
diameters downstream, but when the transducers are positioned this close to any obstruction the resulting errors
can be unpredictable.
Key Point: Do not expect to obtain accurate results if the transducers are positioned
close to any obstructions that distort the uniformity of the flow profile.
Flow
Valid transducer location 10 x Diameter 20 x Diameter
45°
The PUB equipment expects a uniform flow profile as a
distorted flow will produce unpredictable measurement
errors. Flow profile distortions can result from upstream
disturbances such as bends, tees, valves, pumps and other
similar obstructions. To ensure a uniform profile, the
transducers must be mounted far enough away from any
cause of distortion such that it no longer has an effect.
Uniform Flow Profile Distorted Flow Profile
In many applications an even flow velocity profile over
a full 360° is unattainable due, for example, to the
presence of air turbulence at the top of the flow and
possibly sludge in the bottom of the pipe. Experience
has shown that the most consistently accurate results
are achieved when the transducer holders are
mounted at 45° with respect to the top of the pipe.
Possible
sludge
Air
Flow
Transducer
Holder