Rs485 Device Connectivity With The Tpu2000 And Tpu2000R - ABB TPU2000 Technical Manual

TPU2000/2000R Modbus/Modbus Plus/ Modbus TCP/IP Automation Guide

RS485 Device Connectivity with the TPU2000 and TPU2000R

RS485 is one of the more popular physical interfaces in use today. It was developed as an enhancement of the
RS422 physical interface. Its inherent strength is its ability to transmit a message over a twisted pair copper
medium of 3000 feet in length. An RS485 interface is able to transmit and receive a message over such a
distance because it is a balanced interface. That is, it does not reference the signal to the system's electrical
ground, as is the case in an RS232 interface. RS485 references the communication voltage levels to a pair of
wires isolated from system ground. Depending on the manufacturer's implementation, isolation may be optical or
electronic. RS485 has two variants, two wires and four-wire. In the two-wire format, communication occurs over
one single wire pair. In four-wire format, communication occurs over two wire pairs, transmit and receive. The
two-wire format is the most common in use. The TPU2000 and TPU2000R support half duplex two-wire format
only. The RS485 port is also optically isolated to provide for 3000 V of isolation.
The RS485 network supported and recommended by ABB requires the use of three conductor shielded
Suggested RS485 cable and the respective manufacturer's wire numbers are:
•
ALPHA 58902
•
Belden 9729
•
Belden 9829
•
Carol 58902
ABB does not support deviations from the specified cables. The selected cable types listed are of the type which
have the appropriate physical and electrical characteristics for installation in substation environments.
A multi-drop RS485 connection is illustrated in Figure 3-2. Three wires, Positive (Terminal 9), Negative (Terminal
8) and Ground (Terminal 10). RS485 requires a termination resistor at each end of the communication cable. The
resistance shall be from 90 to 120 ohms. Additionally, depending upon the RS485 physical interface converter
used, a pull-up and pull-down resistor may be added to bias the line to decrease the amount of induced noise
coupled onto the line when no communications are occurring. Internal to the TPU2000 and TPU2000R are
jumpers which when inserted in the proper position (as referenced in Figure 3-5), bias the line by inserting the
proper pull-up, pull-down, and termination resistors. To configure the Jumpers J6, J7, and J8, execute the
following procedure:
Refer to Figures 2-4 or 2-5 depending upon the model of Distribution Protection Unit which is
installed.
Refer to Figure 3-6 illustrating the placement of J6, J7 and J8 (or J16, J17, or J 18 on a type 8
card enabling RS 485 for COM 3). J6 (or J16 for COM 3) inserts a 120 ohm resistor between
transmit and receive lines. J7 or (J17 for COM 3) and J8 or (J18 for COM 3) inserts a pull-up and
pull-down resistor. The IN position inserts the associated resistor in to the circuit. The OUT
position removes the resistor from the circuit.
Insert the TPU2000 and TPU2000R unit into the chassis as per the instructions associated with
Figures 2-4 or 2-5.
Tighten the knurled screws at the front of the unit.
IT IS advisable to place a sticker on the front of TPU2000 AND TPU2000R indicating that it
is a terminated end of line unit. This makes maintenance of installed units easier.
The following example illustrates an interconnection of the TPU2000 and TPU2000R with a host device through a
UNICOM physical interface connection using a 3-wire connection method. It should be noted that the RS485
design on ABB relay products incorporates isolation. That is, the RS485 ground is electrically isolated from the
internal circuitry thereby assuring minimal interference from the extreme noise environments found in a
substation. Care should be used when installing an RS485 communication network. The recommended
configuration must be followed as shown in Figure 3-5, 3-6, 3-7, and 3-8. Jumpers J6, J7, and J8 should be
inserted to provide termination and pull-up at the TPU2000 and TPU2000R end. Although not shown, a 120 ohm
resistor should be inserted between the TX/RX + and TX/RX- pairs to provide for termination at the transmission
end.
cable.
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