74
Publication S130E
Issue 1.0
Pakscan IIS Technical Manual
Fig. 15 shows the relationship between cable cross
sectional area, baud rate and length of loop. e.g. using
1.0 mm² cable and a loop length of between 2.6 km and
5.0 km the loop speed will have to be set to 600 baud.
Fig. 16 shows the scanning time, in seconds, for various baud rates, set up on the master station, with various
quantities of FCUs, (doubling in action).
Fig 17 shows the time taken from when the master station sends a
command to when the field unit receives it.
Commands are interleaved between poll messages, so a command is
actioned almost immediately. The time for the feedback response to the
command, e.g. change in digital status resulting from a motor starting, is:
1/2 loop scan time (typical)
loop scan time (worst case)
12.4 External Connections
The single row of terminals towards the bottom of the enclosure are used for all the input and output
connections to the 2 wire loop and the host system comms.
Fig. 18 shows the connections, together with the jumpers and switches that affect the use of some of the
connections.
Terminals 1 to 8 - Comms Port A (1) and Terminals 9 to 16 - Comms Port B (2)
The comms ports are configurable for RS232 or RS485 (2 or 4 wire). In RS232 mode modem control signals
are available. In RS485 mode there are no modem control signals available and switches S1-S3 are used to
select 2 or 4 wire and if this part of the data highway is to have termination resistors connected. Correct line
termination of the RS485 highway is essential if the communications is to be sound.
In 2 wire RS485 mode the connections are made to Tx+ and Tx-.
Baud
Rate
0.5 mm²
1.0 mm²
1.5 mm²
110
6.3
13.5
20.3
300
6.3
8.3
9.5
600
3.8
5.0
5.0
1200
2.6
2.6
2.6
2400
1.3
1.3
1.3
Cable Size
Fig. 15: Loop Length data
Baud
Rate
32 FCU’s
110
4.5
300
1.6
600
0.8
1200
0.4
2400
0.2
Fig. 16: Scanning Time
Baud Rate
Time (ms)
110
432
300
216
600
108
1200
54
2400
27
Fig. 17: Time to issue a command
