Pakscan IIS Technical Manual Issue 1.0
Publication S130E 63
As the master station progresses through the configuration of the loop it moves through a number of steps:
1. It waits for all field units to revert to loopback on. - Waiting for Loopbacks 1
2. It locates each field unit connected to port A - Finding FCU A
3. It locates each field unit connected to port B - Finding FCU B
4. It then waits again for all field units to revert to loopback on - Waiting for Loopbacks 2
5. It removes loopbacks from field units on A as far as the last one on the loop which it leaves in
loopback - Loopbacks Off A
6. It removes loopbacks from field units on B as far as the last one on the loop which it leaves in
loopback - Loopbacks Off B
7. It reports the loop status - Loopback On or Off
The master station should have established communication with the furthest field unit. Return to the Master
Station Status page (section 8.3), press 2 to select Field Units, and select the address for the powered on field
unit by using the 'Up' or 'Down' arrow key. The status screen (as illustrated in section 8.6.1) will show if
communication is established.
Now switch on the next nearest field unit, change the display to show its status and check that communication
is established with it and the last field unit. There is no need to reset the loop as this unit has been introduced
between the master station and the field unit in loopback and communication with it should be quickly
established. If there is a fault on the loop wiring this will prevent the master from communicating to this field
unit.
Successively progress backwards round the loop powering 'on' each field unit and establishing
communications. Faults should be corrected as you go. Switch the display between the field unit being
checked and the Master Station Status screen to make sure that communications are satisfactory. If the master
station fails to locate a field unit, or goes into the reconfiguration process use the diagnostic screens to
establish why. Finally you will end up with all the field units in communication with Port A.
Next connect the Port B wires and disconnect the Port A wires, reset the loop and check that there is only one
loopback at the field unit nearest Port A.
Finally re-connect the Port A wires, reset the loop and check that there are no loopbacks anywhere, and that all
the field units are in communication with the master station. Verify that status changes in the field are reported
to the appropriate field unit screen, and that commands can be issued to every field unit.
10.3 Checking System Performance
In section 9.3 it was recommended to set Baud Rate Doubling ‘OFF’. Once the loop is up and running this
may be changed to 'Doubling On'.
10.3.1 Setting the Loop Driver Voltages
In most systems it is not necessary to trim the loop driver card voltages to optimise the performance. However
for maximum performance the voltages can be set to match the loop cable parameters. The ideal voltage
depends on the loop resistance and the number of field units attached:
Ideal Voltage = Resistance + No.FCU's + 3 Volts
50 50
The two potentiometers, RV181 and RV182, can be set by either of two methods.
