Siemens RUGGEDCOM RX1100, Руководство по установке

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RUGGEDCOM RX1100
Installation Guide
Chapter 3
Communication Ports
Connecting Multiple RS485 Devices 31
Section 3.11
Connecting Multiple RS485 Devices
Each RS485 port can communicate with multiple RS485 devices by wiring devices together in sequence over a
single twisted pair with transmit and receive signals on the same two wires (half duplex). For reliable, continuous
communication, adhere to the following guidelines:
• To minimize the effects of ambient electrical noise, use shielded cabling.
• The correct polarity must be observed throughout a single sequence or ring.
• The number of devices wired should not exceed 32, and total distance should be less than 1219 m (4000 ft) at
100 kbps.
• The Common terminals should be connected to the common wire inside the shield.
• The shield should be connected to earth ground at a single point to avoid loop currents.
• The twisted pair should be terminated at each end of the chain.
The following shows the recommended RS485 wiring.
<
12
19
m
(
40
00
in
)
120Ω 10nF
120Ω 10nF
1
2
3 5
5
6
4
Figure 33: Recommended RS485 Wiring
1. RX1100 Device 2. Common (Isolated Ground) 3. Negative 4. Positive 5. Shield to Earth (Connected At a Single Point)
6. RS485 Devices (32 Total)