Efficient Plant April 2019 - 30

fluid-handling solutions

Highly accurate measurement of volumetric flow is just one of several important benefits that electro-magnetic flow meters provide in fluid-handling processes.

Brush Up on
Mag-Meter Basics
MAG METERS (electromagnetic flow meters) offer a number of benefits in
fluid-handling applications. Among other things, they're obstruction-less,
cost-effective for aggressive chemicals and slurries, and highly accurate in measuring volumetric flow.
Mag meters work by way of an inline sensor that measures induced voltage generated by fluid as it flows through a pipe. The transmitter takes voltage
generated by the sensor, converts it into a flow measurement, and transmits that
measurement to a control system.
Experts with Emerson Flow Solutions, St. Louis (emersonflowsolutions.com),
compiled the following list of some best practices for keeping your mag meters
functioning within their original parameters.
- Jane Alexander, Managing Editor

For more information on fluid-handling/flow-control topics,
visit emersonflowsolutions.com

30

| EFFICIENTPLANTMAG.COM

 Select magnetic flow-sensor materials that are chemically
compatible with all expected process fluids and cleaning/
flushing agents. Beware of steam-out conditions that require a
meter rated for higher temperatures and full vacuum.
 Orient the mag meter properly to keep it full and avoid twophase conditions. Direct flow upward through the meter, if
possible.
 Use recommended upstream and downstream pipe lengths to
ensure proper fluid conditioning for best flow-measurement
results. Consult the manufacturer if space requirements won't
allow the minimum diameters.
 If insulation is used, don't cover the coil housing or electronics
as these components can overheat and fail.
 Size mag meters properly to achieve best flow-measurement
performance across the full process flow range. Most will
perform well when selected to match the process-pipe size.
But, for processes that operate at low flowing velocities, adding
a reducer to accommodate a smaller magnetic sensor will
improve measurement accuracy by increasing the fluid velocity
through the sensor.
 Isolate wiring from the transmitter to the magnetic sensors
in its own conduit. Do not run mag-meter wiring in a conduit
shared with any other equipment wiring. Any electrical interference can cause measurement offsets.
 Avoid stripping too much insulation from mag-meter wiring.
Any exposed wires that aren't covered by a braided shield can
allow extraneous electronic interference into the measurement
circuits.
 Ensure that mag-meter electronics are grounded to the process
fluid (in addition to earth ground) by using ground straps,
ground rings, lining protectors, or a dedicated grounding
electrode.
 Verify that calibration constants from the flow sensor are
reflected properly in the electronics. For sensors capable of
driving the magnetic coils at multiple frequencies, there should
be a unique calibration number for each coil drive frequency.
 Perform a zero calibration if using an AC-powered mag meter,
or when operating at high-coil-drive frequencies on pulsed-DC
meters.
 Determine a field baseline for the circuit-health-monitoringdiagnostic test values (meter verification) if required by the
manufacturer. EP

APRIL 2019


http://www.emersonflowsolutions.com http://www.EFFICIENTPLANTMAG.COM

Efficient Plant April 2019

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