Echelon LONWORKS PLT-22, Руководство пользователя

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PL Transmitter
PL Receiver
Line
Earth
Figure 4.4 Line-to-Earth Coupling Method
To understand the advantage of line-to-earth coupling, recall that a major component
of signal attenuation is due to the loads presented by devices that are connected to
the power mains between the line and neutral wires. These loads do not affect signal
attenuation when line-to-earth coupling is used. Field measurements have shown
consistent improvements in received signal-to-noise ratios of more than 15dB for
transceivers using line-to-earth coupling, relative to transceivers using non-earth-
return coupling. For this reason, when a safety ground connection is known to be
available throughout the wiring system, a line-to-earth coupling scheme is preferred.
In applications where a safety ground connection may not exist, or line-to-earth
coupling is precluded by local regulations, the coupling circuit must be connected
between the line and neutral wires. This style of coupling is known as line-to-neutral
coupling and is shown in figure 4.5.
4-6 Coupling Circuits