Liquid Temperature; Other Liquid Variables; Metering Characteristics - ABB MINI-MAG 10D1475 Series Instruction Manual

10D1475 MINI-MAG MAGNETIC FLOWMETER INSTRUCTION MANUAL

4.2.1.2 Liquid Temperature

Having established the minimum liquid conductivity requirements for a given application, any liquid
which exhibits equal or higher conductivity may be metered without concern for any system compen-
sating adjustments. However, due regard for the effect of the liquid conductivity versus temperature
should be considered.
Most liquids exhibit a positive temperature coefficient of conductivity. It is possible for certain
marginal liquids to become sufficiently non-conductive at lower temperatures so as to hamper
accurate metering. However, the same liquid at higher or normal environmental temperatures may be
metered with optimum results. The possibility of an adverse temperature conductivity characteristic
should be investigated before attempting to meter such a liquid. Process or ambient temperatures are
also limited by the meter materials specification.
Other normal effects of temperature, such as influence upon liquid viscosity and density, the size of
the metering area, and the flux density of the magnetic field, have negligible or no effect upon
metering accuracy.

4.2.1.3 Other Liquid Variables

Other liquid variables such as viscosity, density and liquid pressure have no direct influence on
metering accuracy. Liquid density has no effect on volumetric flow rate since only the area of the
meter pipe and liquid velocity are required to determine the rate of flow. Viscosity and metering
pressure are restricted to physical limitations alone, such as the leakage pressure of the meter pipe
flange connections.

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.
4-4
TABLE 4-1. ELECTRODE DIAMETERS
Meter Size
inch mm
1/10 3
5/32 4
1/4 6
3/8 10
1/2 15
1 - 4 25 - 100
Electrode Diameter
inch cm
0.048 0.122
0.079 0.202
0.142 0.361
0.236 0.600
0.250 0.635
0.312 0.792
FUNCTIONAL DESCRIPTION