Pakscan Overview
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Publication S177E V2.0 Issue 03/05
4
OVERVIEW OF PAKSCAN
The Pakscan system is a control and monitoring
package comprising a master station, 2-wire serial
data cable wired in a ring or loop and a number of
connected actuators with Pakscan field units fitted.
The fieldbus loop can have up to 60, 120, 180 or
240 field units connected depending on the
capability of the master station, and the cable can
be up to 20 km long. The length of the 2-wire cable
(loop length) can be considered as the
circumference of a circle starting and finishing at
the master station.
The master station is a single module in a 19-inch
rack. It may have a supporting, identical, standby
unit. Details of setting a Hot Standby pair are
covered in Section 10. In essence, the Hot Standby
simply comprises two identical master stations each
of which is set identically to its partner. In some
cases two master stations are fitted into one 19-
inch rack (there is space for two). These can be
considered as two independent units.
The current loop is single fault tolerant and can
withstand either an open circuit, short circuit or
ground connection fault and still maintain
communication with all the field units. Subsequent
faults do not stop the complete system from
working and the parts that remain connected to the
master station will continue to be in communication
with it.
In addition to controlling the loop, the master station
also provides the external interface to the system.
It supports 2 serial ports for communications to host
computers, as well as providing a local user
interface. Alternatively, one of the serial ports may
be used to drive a printer to log alarms. In the
Pakscan Ethernet version one or both the serial ports are replaced with a standard 10Base-T Ethernet
ports. When a single Ethernet port is available the remaining serial port may be either RS232 or
RS485 depending on the option chosen.
4.1 Field Control Units
A range of field control units ('FCU’s') is available to cater for specific application areas. These may be
summarised as follows:
Fig 3: Pakscan IIE System Diagram
