Technical reference
A
A.1
Theory of operation
The Coriolis principle of measurement
The flow measurement is based on the Coriolis law of motion. Particles moving in a rotating /
oscillating system will resist imposed oscillations in a manner consistent with their mass and
velocity (momentum).
The SITRANS F C sensors are energized by an electromagnetic driver circuit which oscillates
the pipes at their resonant frequency. Two pickups are placed symmetrically on either side of
the driver to provide position signals for digital processing.
When the media flows through the sensor, Coriolis force will act on the measuring tubes and
cause deflection which can be measured as a phase shift between Pickup 1 and Pickup 2. The
phase shift is proportional to the mass flowrate.
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The frequency (or period) of the vibration is a direct function of the process media density.
The frequency and amplitude of the driver is regulated to ensure a stable output from the 2
pickups. The temperature of the sensor tubes is measured to provide accurate compensation
for changes in the material stiffness. As a result the process media temperature is also
accurately measured.
The flow proportional phase signal from the pickups, the temperature measurement and the
driver frequency enable calculation and reporting of mass, density, volume, and temperature.
SITRANS FC330
Operating Instructions, 01/2019, A5E44030648-AB
225