Table of Contents
Advertisement
Page 2 of 15
RS485 SERIAL PORT
RS485 data transmission and reception is accomplished over a single twisted pair with transmit and
receive data alternating over the same two wires. Using this port, continuous monitoring and control
to a PLC, protection relay or any serial Modbus IED is possible.
Connect the "+", "–" and common terminal of MultiNet to the "+", "–" and common terminals of all the
IEDs. Correct polarity must also be observed. For instance, the IEDs must be connected with all
RS485 "+" terminals connected together, and all RS485 "–" terminals connected together.
To minimize errors from noise, the use of shielded twisted pair wire is recommended. The COM
terminal should be connected to the common wire inside the shield, when provided. To avoid loop
currents, the shield should be grounded at one point only. Each relay should also be daisy-chained to
the next relay in the link. A maximum of 32 relays can be connected in this manner without exceeding
driver capability.
Lightning strikes and ground surge currents can cause large momentary voltage differences between
remote ends of the communication link. For this reason, surge protection devices are internally
provided at the communication port. An isolated power supply with an opto-coupled data interface
also acts to reduce noise coupling. To ensure maximum reliability, all equipment should have similar
transient protection devices installed.
Both ends of the RS485 circuit can be terminated with impedance as shown in Figure 2: Typical
Configuration. Termination networks should only be applied if long cable runs are used
between RS485 connections. A typical load value for a terminating network is a 120-ohm resistor in
series with a 100-pF capacitor.
The termination capacitors are used for AC termination to reduce the power
consumption of the idle link, as well as to reduce the ringing voltage. The negative
NOTE
http://www.GEmultilin.com
Courtesy of NationalSwitchgear.com
Figure 1: Connections
MultiNet
GE Digital Energy
Hide quick links:
Advertisement
Table of Contents
