Circuit Description; Primary Signals; Constant Meter Capacity (Cmc) Pc Assembly - ABB MINI-MAG 10D1475 Series Instruction Manual

10D1475 MINI-MAG MAGNETIC FLOWMETER INSTRUCTION MANUAL

4.3 Circuit Description

4.3.1 Primary Signals

The Model 10D1475J/S flowmeters use integral or remote 50XM1000 Converter electronics. As
described in paragraph 4.1, the magnetic flowmeter body houses two signal electrodes and two flux
producing magnet coils. Refer to the 50XM1000 Converter Instruction Manual for remote-configura-
tion interconnection wiring diagrams. All Flowmeter intraconnection wiring is terminated at the CMC
PC board located in the base of the meter housing.
The Flowmeter provides two output signals to the associated signal converter, an electrode signal
that contains the flow rate information and the reference signal which is proportional to the magnet
excitation current (theoretically, the 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.
The (gated) magnet driver operates at a frequency that permits magnetic flux in the Flowmeter to
reach a steady state level during the last 25% of each half period of magnet excitation. By using
sampling techniques, the flow (differential mode) signal is measured only during the intervals that
magnetic flux is constant:



Therefore, zero instability due to changing flux is eliminated by use of the MAG-X design concept
(sampling technique), providing a meter totally free of zero drift. A thorough discussion of signal
converter operation is provided in the Instruction Bulletin supplied with the particular signal converter.

4.3.2 Constant Meter Capacity (CMC) PC Assembly

The CMC PC Assembly provides several functions. These include:
1. Establishing interconnections between the Flowmeter internal wiring and
the signal converter.
2. Permitting factory adjustment of meter capacity values to a fixed value for
each nominal size Flowmeter.
3. Establishing proper wiring connections for remotely mounted signal con-
verters.
Meter coil current and, consequently, calibration factor are established by adjusting a precision
current-sense network which is in series with the meter coils. The current-sense network consists of
a low-resistance current-sensing resistor along with an adjustable resistive divider network placed
across the current-sense resistor. A potentiometer is also used to provide fine-tuning of the meter
capacity. Should this resistive network be damaged, repair and recalibration are only possible by
using precision electronic calibration instruments.
FUNCTIONAL DESCRIPTION

dΦ
= 0

dt 
4-5