ONICON FB-3500 Series - Manual (Page 27)

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FB-3500 Bi-Directional Insertion Electromagnetic Flow Meter Manual 05/14 - 0718-3
Page 27
IMPORTANT NOTE
Non-metallic pipes are more susceptible to electrical noise. Grounding rings installed upstream
and downstream of the meter location to reduce the electrical noise present in the pipe may be
required for proper operation. Refer to section 1.5.1 of this manual for additional information
on the use of grounding rings.
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Minimizing Electrical Noise
The most effective way to minimize the effects of electrical noise is to make sure that
the pipe, the fluid and the flow meter body are all connected to earth ground. This
accomplishes two important goals. First, it ensures that the pipe, fluid and flow meter are
all at the same electrical potential. Second, it ensures that this electrical potential is
the same as earth ground.
In order to be certain that the meter is properly connected to earth, the flow meter earth
cable should be run directly to a known earth connection. The length of this earth cable
should be as short as practically possible, preferably ≤25 feet in length. The table below
lists earth connections from best to worst. If necessary, a separate earth cable should be
connected to the metal pipe near the meter.
Earth Connections (stranded wire 14 - 18 AWG)
Best Earth grounding rod driven into the ground to the depth of the water table.
Earth wire connected directly to the building electrical service panel.
Worst Earth wire connection inside an electrical outlet near the meter.
Diagnosing Electrical Noise Problems
When diagnosing electrical noise problems, it is important to understand that one of four
possible conditions are likely to exist. They are as listed in the table below. In order to
minimize the effects of noise, it is helpful to understand which of the following conditions
are present.
Earth Connection at
Flow Meter
Pipe / Fluid Earth
Connection
Expected
Noise
Level
Possible Remedies
Good earth connection
≤ 25 feet from flow meter Pipe & fluid are
connected to earth Low None required
Good earth connection
≤ 25 feet from flow
meter Pipe & fluid are not
connected to earth Moderate A separate earth connection can be
made directly to the metal pipe or to the
fluid. Non-metalic pipes may require
grounding rings installed upstream and
downstream of the meter location.
Poor earth connection Pipe & fluid are
connected to earth Moderate Removing the earth connection at the
flow meter may reduce the noise level.
If this is a long wire run, break the
connection where the wire connects to
the cable coming out of the flow meter. If
noise level is still too high, locate a better
earth connection for the flow meter.
Poor earth connection Pipe & fluid are not
connected to earth High Locate a better earth connection for
the flow meter. If noise level is still too
high, locate a better earth connection
for the pipe or fluid.