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10D1476 K-MAG MAGNETIC FLOWMETER INSTRUCTION MANUAL
The electrode diameter is 0.15 cm (0.060") for all meter sizes except 1/25" ((0.020") and 1/12"
(0.040").
For example, assuming the measured ac electrode resistance (full pipe and zero flow) is 190,000
ohms and electrode diameter is 0.15 cm, then
σ =
1
= 55.55 µS/cm
(0.192 - 0.072) x 0.15
This is above the threshold for specified measurement accuracy for the particular liquid, meter size
and Signal Converter combination. Liquid conductivities at the operating temperature may also be
determined from standard reference works for many pure liquids. Field Engineers are equipped to
determine the conductivities of special liquids at the user's site as an engineering service.
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. Liquid 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 as given in Specifications Section 1.3.
4.2.2 Metering Characteristics
The metering pipe must be completely filled at all times for accurate results. See Installation Section
2.0 for piping information. 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 - or - 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 measure-
ments 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 determined 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
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