Rs485 Communications Port - GE GEK-106273L Instruction Manual

Digital feeder protection

Table of Contents

In addition to the RS232 port on the faceplate, the relay provides the user with an additional RS485 communication

port. RS485 data transmission and reception are accomplished over a single twisted pair with transmit and receive

data alternating over the same two wires. Through the use of these port, continuous monitoring and control from a

remote computer, SCADA system or PLC is possible.

To minimise errors from noise, the use of shielded twisted pair wire is recommended. For a correct operation, polarity

must be respected, although if it is not so, there is no danger to damage the unit. For instance, the relays must be

connected with all RS485 SDA terminals connected together, and all SDB terminals connected together. This may

result confusing sometimes, as the RS485 standard refers only to terminals named "A" and "B", although many

devices use terminals named "+" and "-". As a general rule, terminals "A" should be connected to terminals "-", and

terminals "B" to "+". There are exceptions to this rule, such as ALPS and DDS family relays. The GND terminal should

be connected to the common wire inside the shield, when provided. Otherwise, it should be connected to the shield.

To avoid loop currents, the shield should be grounded at one point only. Each relay should also be daisy chained to

the next one in the link. A maximum of 32 relays can be connected in this manner without exceeding driver capability.

For larger systems, additional serial channels must be added. It is also possible to use commercially available

repeaters to increase the number of relays on a single channel to more than 32. Do not use other connection

configuration different than the recommended.

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. To ensure maximum

reliability, all equipment should have similar transient protection devices installed.

M SERIES RELAY

(*) Line terminations (120 ohm / 0.5 W + 1 nF / 100 V)

3-38

PRODUCT DESCRIPTION

SDA

B12

SDB

A12

B11

GND

SDA /-

SDB /+

GND

Zt (*)

should be used when length of line exceeds 1 km.

Figure 3-10 RS485 SERIAL CONNECTION (B6366H5)

MIF Digital Feeder Protection

3.2.8.