Functional Description; Basic Operating Principle; Signal Voltage Generation - ABB MAG-X 3000 Series Instruction Manual

INSTRUCTION MANUAL 10DX3111A&G Sizes 14 - 24 Inches

4.0 FUNCTIONAL DESCRIPTION

The Magnetic Flowmeter body houses two signal electrodes and the flux producing magnet coils, as
shown pictorially in Figure 4-1. Normally, the meters have their primary interconnection wiring
terminated at a printed circuit assembly located in the base of the meter housing. A cable connects
the Primary meter housing to the remote Signal Converter. This interconnection wiring is shown in
Figures 2-9 & 2-10 for Models 10DX3111A & 10DX3111G respectively.
The primary provides two output signals to the associated Signal Converter:
• an electrode signal that contains the flow rate information
• the reference signal which is proportional to the magnet excitation current (This
reference signal is proportional to the flux density in the metering section.)
The reference voltage is derived across a precision "constant meter factor" resistance network that is
connected in series with the magnet coils. Changes in magnet drive voltage, which cause a variation
of flow signal, will simultaneously cause a proportional variation of the reference voltage. The
circuitry will provide an exact ratio and thereby provide immunity to power supply variation. The
magnet coil drive circuitry is contained in the Signal Converter. A detailed discussion of primary
meter operation is provided in Chapter 5.0, Circuit Description.

4.1 Basic Operating Principle

4.1.1 Signal Voltage Generation

The operating principle of the ABB Automation Series 3000 Magnetic Flowmeter is based upon
Faraday's Law of Induction which states that the voltage induced across any conductor as it moves
at right angles through a magnetic field will be proportional to the velocity of that conductor. This
principle finds common application in direct and alternating current generators. Essentially, the ABB
Automation Magnetic Flowmeter constitutes a modified form of an ac generator.
FIGURE 4-1. BASIC OPERATING PRINCIPLE
Figure 4-1 graphically illustrates the basic op-
erating principle. A magnetic field, "B", being
generated in a plane which is perpendicular
to the axis of the meter pipe. A disk of the
metered liquid can be considered as a con-
ductor. The transverse length "D" is equal to
the meter pipe diameter. Since the velocity
"V" of the liquid disk is directed along the axis
of the meter pipe, a voltage, signal "E
be induced within this liquid which is mutually
perpendicular to the direction of the liquid
velocity and the flux linkages of the magnetic
field; i.e., in the axial direction of the meter
electrodes.
", will
s
4-1