Pakscan IIE System Manual
110 of 132
Publication S177E V2.0 Issue 03/05
13.3 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'.
13.3.1 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 can be set by either of two methods.
Method 1
Turn both potentiometers fully anti-clockwise. This sets the voltage to the maximum.
To set Port A's voltage.
Disconnect the two wires from Port B and re-configure the loop. With the
loop running, turn Port A's potentiometer RV101 clockwise until the A LED on the door just goes out.
Then turn the potentiometer back slightly until the A LED is fully lit once more.
To set Port B's voltage.
Reconnect the two wires at Port B, and disconnect the two wires at Port A.
Re-configure the loop. With the loop running, turn Port B's potentiometer RV102 clockwise until the B
LED on the door just goes out. Then turn the potentiometer back slightly until the B LED is fully lit once
more.
Reconnect the two wires at Port A. Re-configure the loop and leave it running for a few minutes.
Check that communication with all field units is satisfactory.
Method 2
With the field units powered up the master station should be able to communicate to all of them once
the loop has been configured. If communications are not fully established see Section 13.4 for fault
finding hints.
The line drive voltage can now be set with the aid of an oscilloscope. Allow the master station to
configure the loop and ensure all field units are in communication without any loopbacks.
Monitor across Port A loop wires and trim
V
max down to
V
ideal by adjusting Port A's potentiometer.
(See Figure 40)
Remove Port A wires, allow reconfiguration to finish, again checking all field units are in
communication with only one unit in loopback (which should be the one that was connected directly to
port A). Monitor across Port B loop wires and trim
V
max down to
V
ideal by adjusting Port B's
potentiometer. Remove the oscilloscope and replace the field loop wires and reset the loop.
