Metering Characteristics; Circuit Description; Primary Signals - ABB COPA-XM 3000 Series Instruction Manual

Series 10DX3000 Magnetic Flowmeter Instruction Manual

4.2.2 Metering Characteristics

The metering pipe must be completely filled at all times for accurate results. Where there is
possibility of operation with a partially filled horizontal pipeline, it is recommended that the magnetic
flowmeter be installed in a vertical section of that pipeline such that liquid flow moves upward. A
vertical installation also offers the advantage of an even distribution of liner wear in the event that
solid abrasives are being carried along in the liquid stream.
The magnetic flowmeter will measure the total amount of material passing in the liquid stream. The
meter will not, for instance, differentiate between the amount of liquid and the amount of entrained
gases. Also, in the case of a slurry, it will not differentiate the amount of liquid from solids. If the liquid
to mixant ratio is of importance to process control, then separate measurements of the concentration
of the desired medium must be made and appropriate correction factors must be applied to the
magnetic flowmeter output.
In applications involving variable quantities of uniformly dispersed, non-conductive mixing agents, it
must be ascertained that the higher concentrations of mixant will not drive the average conductivity
of the liquid mixture below the minimum conductivity level for the given installation.

4.3 Circuit Description

4.3.1 Primary Signals

The Model 10DX3111E 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 Manual supplied with the particular signal converter.
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