5707070-A Installation and Operation 2-5
Sono-Trak™ Doppler Ultrasonic Flow Meter
Assessing Pipe Material and Condition
Doppler flow meter performance is best maximized by using piping that is sonically
conductive. The Doppler flow meter assumes that the path by which the ultrasonic
beam enters the pipe and returns to the transducer is ultrasonically homogenous,
which means that you must use your flow meter with pipes with non-porous smooth
pipe walls. Concrete-lined pipes, old or crystallized cast iron pipes, hand-wrapped
fiberglass pipe, and old piping with air inclusions do not exhibit the required
homogeneity. Avoid using the Doppler flow meter for flow measurement on these
pipes unless proper operation is proven by the manufacturer through demonstration.
Contact “EMCO Flow Systems Support” on page 3-11 for more information on an
alternate meter if your application is not suitable for the Doppler flow meter.
Note: No clamp-on meter will operate properly if the liner is not solidly attached to
the pipe wall because of the probability of an air gap.
Pipe Vibration
Moderate pipe vibration does not usually adversely affect the Doppler flow meter,
since the vibration of the piping is at a significantly lower frequency than the
ultrasonic beam used to measure flow. However, in situations where the transducer
signal strength is low because of fluid, piping, or other environmental factors,
measurement accuracy may be further decreased by pipe vibration. In these situations
your display panel may register flow when there is none due to the vibration. If you
can not bracket the pipe to reduce vibration, you may be able to rectify the problem by
relocating the transducer to a pipe location with less vibration.
Assessing Flow Profile
STRAIGHT RUN REQUIREMENTS
As with other flow meters such as vortex or magnetic flow meters, the Doppler flow
meter needs a well-developed flow profile to ensure accurate flow measurement. To
assure a well-developed profile, choose a measurement point on a long run of pipe—
well away from elbows, valves, pumps, flanges, and other possible sources of
turbulence.
The ideal placement of the Doppler flow meter is with 20 diameters of straight run
upstream and 10 diameters of straight run downstream between the transducers and
any disturbance of the flow. Most typical flow meter applications use 10 diameters of
straight run upstream and 5 diameters downstream from any disturbance of the flow.
However, when the measured fluid is too clean to provide the proper number of
reflective particles, one may position the transducer near the pump or source of
turbulence in such a manner as to obtain stable readings in a continuous flow full pipe
situation. Using a transit time meter may be another viable option if the Doppler flow
