Description
September 2018
TRB-UM-00478-EN-01
Page 4
DESCRIPTION
The Exact Dual Rotor turbine flow meter uses a unique rotor design that reduces swirl
effects These flow meters are designed and manufactured to the highest quality standards
to provide the best possible performance for flow measurement requirements
Traditional Operating Principle
A turbine flow meter, in its base form, measures fluid velocity As a fluid passes through the
meter, the velocity of the fluid presses rotational energy on the internal rotor assembly The
rotor blades generate pulses proportional to flow as they pass through a radio frequency
field created by a pickup Each pulse is transmitted to the meter electronics, where it
amplifies the pulse output and provides a volumetric flow rate
Dual Rotor Advantages
The dual rotor design eliminates many of the problems associated with traditional single
rotor designs The hydraulic coupling of the two rotors reduces the fall-off of the output
frequency at low flow rates, extending the usable range, or turndown ratio Additionally,
swirl at the meter inlet, which causes a significant inaccuracy in a single rotor meter, is
largely canceled by summing the counter-rotating rotor signals
Performance
The performance of any turbine flow meter is affected by three forces, which can cause the
output signal to become non-linear: bearing friction, viscous drag, and magnetic drag (from
magnetic type pickups) Bearing friction is minimized by using exceptionally high quality
ball bearings Viscous drag, which is a function of the metered fluid, cannot be eliminated
Magnetic drag is eliminated by the use of modulated carrier (RF) pickup coils
Bearing friction and viscous drag are accounted for by calibrating the flow meter on a
primary standard positive displacement liquid flow meter calibrator
MATERIALS
Body
316 stainless steel
Shafts
316 stainless steel
Rotors
17-4 PH stainless steel
Bearing
Ceramic ball, with hybrid corrosion resistant raceways
Nuts
ASTM A286
Spacers
303 stainless steel
Supports
303 stainless steel
Transitions
302 stainless steel
