5707070-A Introduction and Theory of Operation 1-3
Sono-Trak™ Doppler Ultrasonic Flow Meter
Sonic Reflectors
The Doppler flow meter requires sonic reflectors in order to operate. These reflectors
may consist of particles or air bubbles within the flow to be measured. Your readings
may vary slightly with changes in concentration or size of these reflectors as well as
the pipe condition and size.
Note: Glycerin is the only known industrial liquid today that is not sonically
conductive.
The Doppler flow meter uses two similar transducers to sense flow in a pipe. These
transducers are mounted on the outside of a pipe. This configuration presents no
obstruction to flow, and will not cause associated pressure drops.
Accuracy
The Doppler flow meter output signal is linear (as opposed to square root), which
means that accuracy is not a function of flow rate. Within certain application limits,
the meter is ideal because it is not affected by changes of pressure within the process
nor by changes of viscosity, temperature, specific gravity, sound velocity, or electrical
conductivity.
Summary
The Doppler flow meter is a non-intrusive flow meter system which operates by
sensing the frequency shifts of signals reflected from particles, air bubbles, or density
differences within a liquid, producing a linear signal proportional to the flow of the
liquid within the pipe.
• No pipe section is required to install the meter.
• The meter is not affected by changes in temperature, viscosity, specific gravity, or
the speed of sound within the liquid.
• The liquid does not have to be electronically conductive.
• A minimum particle concentration of 35 ppm @ 40 micron of suspended solids or
air bubbles is required.
• The reflector must have at least a 0.2% density difference than the liquid medium.
• For accurate volumetric measurement the pipe must be full at all times.
• The sensors, transducer crystals, are always coupled to the pipe with gel or epoxy.
• In order to obtain accurate measurements adequate upstream and downstream
pipe runs are required. Recommended straight-run requirements from any
disturbance of flow are 10 diameters upstream and 5 diameters downstream.
