26
Publication S130E
Issue 1.0
Pakscan IIS Technical Manual
c) Cable Capacitance
The capacitance between the cores, and to the screen, is critical to the system performance. Too high a
capacitance for the selected loop baud rate will result in poor communications, or even communication failure.
Disconnect the join between the 2 cores that connect to Port B, the cores and screen are now all separated.
With your digital meter set to Capacitance, measure the core to core capacitance, and note it down. Also
measure the core to screen capacitance, which will probably be slightly higher. If any problems are
encountered during these tests rectify them before proceeding.
Once these checks have been made the 2 wire cable should be connected to the master station. The power may
now be applied to the system taking care to ensure that the plant is in a safe state and all the actuators are in
local control.
1.
Resistance of core 1
=
2.
Resistance of core 2
=
3.
Resistance between core 1 and
core 2
=
(must be more than 100k
4.
Total resistance of both cores
[should be sum of (1) and (2)]
=
(must be less than 500)
5.
Cable to screen resistance
[should be a high value]
=
6.
Screen to earth resistance
[should be high]
=
7.
Capacitance core to core
=
8.
Capacitance core 1 to screen
=
9.
Capacitance core 2 to screen
[should be the same as( 8)]
=
Results of Cable Checks
