Dwyer UFM - Manual (Page 7)

F - UFM
Issue 1.4 Page 7
4
Installing the UFM
Figure 3 Location of Transducers
In many applications an even flow velocity profile over a full 360° is unattainable due to the
presence of air turbulence at the top of the flow and possibly sludge at the bottom of the pipe.
Experience has shown that the most consistently accurate results are achieved when the
transducer guide rails are mounted at 45° with respect to the top of the pipe.
The UFM equipment expects a uniform flow profile, as a distorted flow will produce
unpredictable measurement errors. Flow profile distortions can result from upstream
disturbance 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.
To obtain the most accurate results the condition of both the liquid and the pipe must be
suitable to allow ultrasound transmission along the predetermined path. It is important that
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 3. 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 mounted 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 obstruction that distorts the uniformity of the flow profile.
Possible Air
Possible
sludge
Guide
rail
Uniform Flow Profile Distorted Flow Profile
Flow
Flow
Valid transducer location 20 x Diameter
10 x Diameter
45°