Siemens MAG 1100, Руководство по эксплуатации, Страница: 81 / 665

6
SITRANS F M
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1. Product introduction
U
i
= When an electrical conductor of length L is moved at velocity v, perpendicular to the lines of
flux through a magnetic field of strength B, the voltage U
i
is induced at the ends of the conductor
Ui = L x B x v
Ui = Induced voltage
L
= Conductor length = Inner pipe diameter = k1
B = Magnetic field strength = k2
v
= Velocity of conductor (media)
k = k1 x k2
Ui = k x v, the electrode signal is directly proportional to the fluid velocity
A flowmeter consists of a sensor (MAG 1100, MAG 1100 F, MAG 3100, MAG 3100 P or MAG 5100 W)
and a transmitter (MAG 5000 or 6000).
SENSOR
The sensor converts the flow into an electrical voltage (U
i
) proportional to the velocity of the flow.
The sensor is built up of a stainless steel pipe, 2 coils, electrodes, an isolating liner, housing and,
where applicable, connecting flanges.
TRANSMITTER
The transmitter consists of a number of function blocks which convert the sensor voltage into flow
readings.
Power supply
Two different types of power supply are available. A 12 ... 24 V AC/DC and a 115 ... 230 V AC 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
extremely high: >10
14
Ω
which allows flow measurements on fluids with conductivities as low as
5
μ
S/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 transmitter 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 transmitter
is therefore unsurpassed with a turn down ratio of minimum 3000:1.
CAN communication
The transmitter operates internally via an internal CAN communication bus. Signals are transferred
through a signal conditioner to the display module, and to/from 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 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.
1.2
Mode of operation The flow measuring principle is based on Faraday’s law of electromagnetic induction.