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

4.0 FUNCTIONAL DESCRIPTION

The meter body houses two signal electrodes and two flux producing magnet coils, as shown
schematically in Figure 4-1. All flowmeter intraconnection wiring is terminated at a printed circuit
assembly located in the base mounted on the meter housing.
The meter provides two output signals to the signal converter:
• an electrode signal that contains the flow rate information
• the reference signal which is proportional to the magnet excitation current
(theoretically, this reference signal is proportional to the flux density in the metering
section).
The reference voltage is derived across a precision constant meter capacity (CMC) 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.

4.1 Basic Operating Principle

4.1.1 Signal Voltage Generation

The operating principle of the Series 3000 meter 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 meter constitutes a modified form of a
generator.
FIGURE 4-1. BASIC OPERATING PRINCIPLE
10DS3111E INSTRUCTION MANUAL
Figure 4-1 graphically illustrates the basic op-
erating principle. A magnetic field, "B", being
generated in planes which are 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
induced within this liquid which is mutually
perpendicular to the direction of the liquid ve-
locity and the flux linkages of the magnetic
field; i.e., in the axial direction of the meter
electrodes. This electrode voltage is the sum-
mation of all incremental voltages developed
within each liquid particle that passes under
the influence of the magnetic field.
", will be
s
4-1