15
I
OFFSET
2
U, I
0
Arc
U-command
Command ramp value
after start signal
(e.g. 100 V/s)
Threshold
I
t
OFF
I
OFFSET
1
t
Adjusting parameters for arc watchdog
The power source output current is measured constantly. The present output voltages
are compared with the defined minimum current values (I
OFFSET
1) and the total of the
average output voltage over time and I
OFFSET
2.
If an arc appears in the plasma process, the plasma voltage collapses. As a result, the
output voltage rises rapidly and exceeds the set threshold value. The arc watchdog
switches off the power module for the duration specified in t
OFF
. After that, the output
voltage increases again at 100 V/s or at the maximum ramp value up to the specified
command value.
The maximum ramp value is about 6500 V/s and depends upon the palsma current
cable length.
I
OFFSET
1 and I
OFFSET
2
Adjustable para-
meters
-
I
OFFSET
1 - STAT
-
I
OFFSET
2 - DYN
-
Sensitivity
The parameters are set using the „Threshold“, „IO1 STAT“ and „IO2 DYN“ DIP switches
on the PLI 10 PC board.
Explanatory Note
Maximum system
threshold
The maximum threshold value of a system is calculated as follows:
Threshold value
max
= n x 60 A + 10 A
n ............ Number of power sources in a system
60 A ....... maximum operating current of a power source
10 A ....... Spare
e.g.:
If there are 3 power sources in a system, the maximum threshold value is 3 x 60 + 10 A,
i.e. 190 A.