Dynasonics PFP-600 - Manual (Page 5)

SECTION 3
THEORY OF OPERATION
The Dynasonics PFP-600 partially filled pipe flow meter combines a traditional clap-on
Doppler type velocity sensor with a unique non-invasive bottom-up level monitor to
accurately determine volumetric flow in horizontal pipes that have dynamically changing
velocity and level characteristics. Unlike traditional velocity sensing flow meters which
assume a full pipe condition and make volumetric flow calculations based on a known
fixed cross-sectional pipe area, the Dynasonics flow meter senses both velocity and
level which allows the micro-processor based electronics to calculate the cross-
sectional area of pipe that is displaced by the liquid and then factored by the sensed
velocity to determine volumetric flow data, regardless of the liquid level in the pipe.
This distinctive technology allows the user to address partially filled pipes as never
before. The major advantages to this type of technology are unparalleled by other
partially filled pipe flow metering devices. First the Dynasonics PFP-600 is non-
invasive. This is extremely important in applications where liquid contact is undesirable.
Secondly, because the systems sensors are located external to the pipe, installation
costs are considerably lower. Finally, because the sensors have no moving parts, are
insensitive to coating materials, or have no pressure sensing ports to clog the system it
is virtually maintenance free.
The PFP-600 is designed around three basic building blocks. The Doppler velocity
sensing electronics, the non-invasive level monitor, and a micro-processor which
controls the timing of velocity and level sensing sequences. The micro-processor
evaluates the flow and level data and calculates the instantaneous volumetric flow, the
total volumetric flow, and drives the 4-20 mA dc output for recording instantaneous
volumetric flow information.
The velocity sensor is a Doppler type sensor. This sensing methodology requires that
the liquid being sensed contain a minimum of 25 PPM of 30 micron suspended particles
3