2
Information.
•
The advanced process recorder is extended by the
addition of a serial data communication option
designed for use with SCADA systems.
•
RS422/485 Communication Standard.
•
Modbus RTU protocol – for master (host computer) to
slave (process recorder) system.
•
Isolated (500V) from rest of instrument.
•
5-wire communication supported.
•
Baud rate – from 1200 to 9600.
•
Parity-checking – odd, even or none.
2
ELECTRICAL INSTALLATION
1
INTRODUCTION
2.1
Selection of Serial Communication Adaptors
for Personal Computers
Information.
•
A RS422/485 communication board is required in the
host PC.
•
Observe the limitations outlined in
Section 7 of the User
Guide. The maximum serial data transmission line
length for both RS422 and RS485 systems is 1200m.
An RS422/485 communications adaptor is required for serial
links. It is strongly recommended that the card used has
galvanic isolation to protect the computer from lightning
damage and increase immunity from noise pick-up.
2.2
Recommended OPTO22 Boards
The following OPTO22 boards are recommended for use with
the advanced process recorder:
Part No.
Computer Type
AC24 AT
AT Bus IBM PC compatible
AC34
Microchannel IBM PC.
2.3
Pull-up and Pull-down Resistors – Fig. 2.1
To prevent false triggering of the slave (process recorder) by
the presence of noise when the master (host computer) is
inactive, 1.8k
Ω
pull-up and pull-down resistors must be fitted
to the RS422/485 adaptor card – see Fig. 2.1.
Fig. 2.1 Pull-up and Pull-down Resistors
1.8k
Ω
Pull-up
Resistor
1.8k
Ω
Pull-down
Resistor
Rx+
Rx–
Tx+
Tx–
+5V
+5V
0V
Computer Terminal or Host Computer
1
2
3
4
5
F
TB1
TB2
TB3
TB4
6
7
8
9
10
0V
1.8k
Ω
Pull-up
Resistor
1.8k
Ω
Pull-down
Resistor
GND
Process Recorder