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Figure 10: RS-485 Connections
Additional connections are provided as jumpers for connecting more RS-485 devices. The two A and B terminal pairs are internally
connected.
The A(-) and B(+) connections are differential providing excellent noise immunity and the third connection is the common input which
gives a reference for the other lines. A shield should also be used to shunt away the noise and because the RS-485 circuit is completely
isolated the shield can be used for the common connection as well. A typical installation is shown in Figure 11.
Figure 11: Typical installation where the shield and ground are used together
The wiring for the A(-) and B(+) should be twisted pair 50Ω impedance cable for better signal quality. A 120Ω termination resistor is
provided on the board and is enabled by placing the provided jumper across the resistor symbol. The termination resistor may not be
required if the RS-485 run is less than 10 meters and there are only two devices within the network. The termination resistor should
only be used on the last device in the series of devices. Typically, the termination should be applied at both ends of the cable. An
additional termination resistor may be required at the master. For most installations start with no termination. If communication
issues are observed then apply the termination to reducing ringing.
WIND SENSOR CONNECTIONS
Two different styles of the wind anemometer sensor are supported, the Mini Aervane (typical) and an optional ultrasonic anemometer.
See Wind Sensor Selection (Register 206) for selecting which type is used.
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