ONICON FB-3500 Series - Manual (Page 22)

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FB-3500 Bi-Directional Insertion Electromagnetic Flow Meter Manual 05/14 - 0718-3
Page 22
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.
IMPORTANT NOTE
Under certain circumstances, connecting the meter to earth through the green/yellow earth wire
may increase the amount of electrical noise present at the meter. Contact ONICON for technical
assistance if you experience increased noise levels with the earth wire connected to earth.
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3.5.2 Earth Connection
FB-3500 Bi-Directional Electromagnetic Flow Meters are designed to detect microvolt
signal levels at the electrodes located on the sensor head. These signals are generated
as conductive fluids flow through the magnetic field generated by the meter. If enough
random electrical noise is present at the electrodes, it can interfere with the flow
measurement. Care must be taken during installation to minimize the effects of electrical
noise on the flow meter.
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, and 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
Earth wire connected directly to the building electrical service panel.
Worst Earth wire connection inside an electrical outlet near the meter.