Badger Meter Vortex Meters - Manual (Page 5)

5 09-VRX-UM-00408 07/12
INTRODUCTION
The RNL vortex shedding fl ow meters are designed to provide accurate and repeatable liquid fl ow measurements in a variety
of common fl ow measurement applications. The fl ow meters employ a patented ultrasonic technique to measure a form of
turbulence created in the fl ow stream. This turbulence, know as a Von Karman Vortex Street, is related to the volumetric fl ow
through a full pipe.
An everyday example of a vortex shedding phenomenon is a fl ag waving in the breeze: the fl ag waves due to the vortices
shed by air moving across the
fl agpole.
Within the fl ow meter, as a fl uid
moves across a strut or “bluff body”,
vortices are also shed but on a
smaller scale. The vortices form
alternately, from one side to the
other, causing pressure fl uctuations.
The alternating pressure changes are
detected by the piezoelectric crystals
in the sensor tube, and are converted
to an analog signal or pulse output.
The frequency of the vortices is
directly proportional to the fl ow. This
results in extremely accurate and
repeatable measurements with no troublesome moving parts (see Figure 1).
The fl ow meters primary output is a 4-20 milliampere (mA) current. The value of the current output is proportional to the fl ow
rate. The secondary output is a pulse train whose frequency is directly proportional to the fl ow.
Each RNL fl ow meter is calibrated against fl ow standards traceable to NIST (National Institute of Standards and
Technology).
The RNL fl ow meter is an insertion style retractable fl ow meter, for pipe sizes 4 inches (102 mm) and larger. The meter is
usually installed through a 2 inch full port isolation valve (See Figure A4), which permits the meter to be retracted or inserted
without shutting down the system.
The RNL series fl ow meters are calibrated in actual volumetric fl ow rates, such as gallons per minute (GPM) and comes with a
standard rate and total display.
T
R
Transmitter
Receiver
Bluff
Body
Ultrasonic
Beam
Counter
FIGURE 1 - VON KARMAN VORTEX STREET