Theory Of Operation - Siemens SITRANS F Operating Instruction

Description

3.1 Theory of operation

Table 3- 1
DN10
DN15
DN25
3.1 Theory of operation
The flow measuring principle is based on the Coriolis law of motion.
Particles moving in a rotating / oscillating system will resist the imposed oscillations in a
manner consistent with the mass and velocity (momentum). Oscillations produced by a
Coriolis flowmeter as the process media is accelerated around bends result in phase
distortions of the measuring tubes.
The SITRANS F C sensors are energized by an electromechanical driver circuit which
oscillates the pipe at its resonant frequency. Two pickups, S1 and S2, are placed
symmetrically on either side of the driver.
When the media flows through the sensor, Coriolis force will act on the measuring tube and
cause a tube deflection which can be measured as a phase shift between pickup S1 and
pickup S2.
The phase shift is proportional to the mass flowrate. The frequency and amplitude of the
driver is automatically regulated to ensure a stable output from the 2 pickups in the region of
80 to 110 mV. The temperature of the sensor tubes is measured by a Pt1000, in order to
enable 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.
SENSORPROM
All SITRANS F C Coriolis flow meters feature a SENSORPROM memory unit which stores
sensor-specific calibration data and transmitter settings for the lifetime of the product. The
factory settings matching the sensor are stored in the SENSORPROM. At commissioning the
flow meter commences a typical flow measurement without any initial programming. Also
customer-specified settings are downloaded to the SENSORPROM.
Figure 3-2
14
Pressure / Measurement
Pressure
PN350
PN350
PN214
SENSORPROM memory unit
Max. massflow
42 kg/min
200 kg/min
500 kg/min
Operating Instructions, 02/2011, A5E02508199-01
SITRANS FCS200