Functional Description - ABB CK-MAG 10D1477 Instruction Manual

10D1477 MAGNETIC FLOWMETER INSTRUCTION MANUAL

4.0 FUNCTIONAL DESCRIPTION

The magnetic flowmeter body houses two signal electrodes, each with associated buffer amplifier,
and the flux producing magnet coils, as shown schematically in Figure 4-1. All primary intraconnec-
tion wiring is terminated at a printed circuit assembly located in the base of the meter housing (see
Figure 3-2).
The primary provides two output signals to the associated signal converter:
• a buffered 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 factor" (CMF) 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.
FIGURE 4-1. BASIC OPERATING PRINCIPLE
4-1