Mode Of Operation - Siemens MAG 1100 Handbook

SITRANS F M MAGFLO
1.2

Mode of operation


1. Product introduction
The flow measuring principle is based on Faraday's law of electromagnetic induction. The flowmeter
consists of a sensor type MAG 1100, MAG 3100 or MAG 5100 W and a signal converter type MAG
5000 or 6000.
U = When an electrical conductor of length L is moved at velocity v, perpendicular to the lines of flux
i
through a magnetic field of strength B, the voltage U
U i = L x B x v
U i = Induced voltage
L = Conductor length = Inner pipe diameter = k 1
B = Magnetic field strength = k 2
v = Velocity of conductor (media)
k = k 1 x k 2
U i = k x v, the electrode signal is directly proportional to the fluid velocity
SENSOR
The sensor converts the flow into an electrical voltage (U
The sensor is built up of a stainless steel pipe, 2 coils, electrodes, an isolating liner, housing and
where applicable, connecting flanges.
SIGNAL CONVERTER
The signal converter consists of a number of function blocks which convert the sensor voltage into
flow readings.
Power supply
2 different types of power supply are available. A 12 - 24 V a.c./d.c. and a 115 - 230 V a.c. switch
mode type.
Coil current module generates a pulsating magnetizing current that drives the coils in the sensor.
The current is permanently monitored and corrected. Errors or cable faults are registered by the self-
monitoring circuit.
Input circuit amplifies the flow proportional signal from the electrodes. The input impedance is
14
extremely high: >10
1 mS/cm. Measuring errors due to cable capacitance are eliminated due to active cable screening.
Digital signal processor converts the analog flow signal to a digital signal and suppresses
electrode noise through a digital filter. Inaccuracies in the signal converter as a result of long-term
drift and temperature drift are monitored and continuously compensated for via the self-monitoring
circuit. The analog to digital conversion takes place in an ultra low noise ASIC with 23 bit signal
resolution. This has eliminated the need for range switching. The dynamic range of the signal
converter is therefore unsurpassed with a turn down ratio of minimum 3000:1.
CAN communication
The signal converter operates internal via an internal CAN communication bus. Signals are
transferred to/from a signal conditioner to the display module, internal/external option modules and
the dialog module.
Dialog module
The display unit consists of a 3-line display and a 6-key keypad. The display shows a flow rate or
a totalizer value as a primary reading.
Output module converts flow data to an analog, a digital and a relay output. The outputs are
galvanically isolated and can be individually set to suit a particular application.
DKFD.PS.027.W3.02
Ω which allows flow measurements on fluids with conductivities as low as
is induced at the ends of the conductor
i
) proportional to the velocity of the flow.
i
5