Principles of operation
The basic principle of this flowmeter employs the frequency shift (Doppler
Effect) of an ultrasonic signal reflected by suspended particles or gas
bubbles (discontinuities) found in liquid flow.
These non-invasive Doppler ultrasonic flowmeters measure liquid flow from
the outside of full pipes. A typical system incorporates a transmitter
w/totalizer and a transducer. The transducer is mounted to the
exterior of the pipe.
An ultrasonic signal, generated by the transmitter,
is emitted through the transducers into the flowing liquid and is
then reflected back by the discontinuities. The transmitter measures the
difference
between
the output and input frequency and converts the frequency difference into
electronic pulses. These pulses are scaled and totaled for flow quantity.
Both portable and dedicated transmitter/display units are available.
In clean fluid applications where insufficient particles or bubbles exist,
the transducers are mounted at a point in the piping where non-symmetrical
turbulence will be experienced. This is done by simply mounting the transducers
after a 90 degree pipe elbow. In this case, the reflections are from the
local turbulence of flow caused by the pipe configuration.
The electronics include digital filtering and recognition circuitry
to reshape the distorted signal into an ideal model, providing a usable
linear measurement.
Typical applications: Sewage, sludge, slurries, paper stock,
paper pulp, petrochemical, caustic, acids, additives, wastewater, and many
other liquids commonly found in plants.
Requirements: A minimum
of 25 ppm of solids or bubbles, of 30 microns or larger. On clean water
service an elbow is required. A full pipe is needed.
Things to Avoid: Rubber,
copper, cement, brass and nickel alloy piping materials. All piping materials
that will absorb the ultrasonic signal. |
