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F-3500 Insertion Electromagnetic Flow Meter Manual 02/18 - 0665-11 Page 23
CAUTION
Failure to provide a proper earth connection to the meter may result in excessive electrical
noise that will interfere with the operation of the meter.
3.5.2 Earth Connection
F-3500 Electromagnetic Flow Meters are designed to detect microvolt signal levels at the
electrodes located on the sensor head. These signals are generated as conductive uids
ow through the magnetic eld generated by the meter. If enough random electrical noise
is present at the electrodes, it can interfere with the ow measurement. Care must be
taken during installation to minimize the effects of electrical noise on the ow meter.
The most effective way to minimize the effects of electrical noise is to make sure that
the pipe, the uid and the ow meter body are all connected to earth ground. This
accomplishes two important goals. First, it ensures that the pipe, uid and ow 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 ow 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.
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.
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.
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