Thermal Dynamics PAK Master 150XL, Руководство по обслуживанию

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Manual 0-2728 4-3 SERVICE TROUBLESHOOTING
4.03 System Theory
The Cutting System is designed for hand cutting and
simple mechanized operation using the torch control bulk-
head as the interface.
A. Logic PC Board Functions
NOTE
Refer to Appendix 4 for Logic PC Board layout.
The Logic PC Board controls the timing and sequenc-
ing of the system. It monitors the pressure, tempera-
ture, and flow interlocks and controls the gas flow in
run and set modes by turning on the plasma and sec-
ondary solenoids. The Logic PC Board also controls
the power on the voltage selection and prepurge func-
tions.
After the ON/OFF switch is closed on the front panel,
the AC Indicator blinks and the GAS Indicator is on
steady. The AC Indicator blinks for approximately 8
seconds then at that time it becomes steady and the
inrush relay closes. The GAS Indicator stays on for
approximately 20 seconds (prepurge function) then
goes off and the gas stops flowing.
When the torch switch is pressed, D26 "start" Indica-
tor comes on, gas will flow for approximately 2 sec-
onds before DC is established (indicated on the front
panel). During this time D25 CD Enable will come
on and sends a logic signal to the CD Board which
fires the spark gap and initiates the torch to pilot. D25
should go out immediately if the pilot starts imme-
diately.
When the torch is close to the workpiece, the cutting
arc "transfers" to the work. Also, if the tip touches
the workpiece, the current is automatically folded
back to approximately 35 amps to save the tip from
being blown out.
The resulting current is sensed by the Current Sense
PC Board, resulting in the demand level changing
from pilot current to whatever the main current con-
trol is set at. During the "transfer" the CSR Indicator
(D65) comes on and the transfer enable signal goes
low allowing the bottom gate drive and FET mod-
ules to come up and start running. Also at this time,
D5 (located on the Pilot Output PC Board) shuts off
and at this time the main cutting arc is initiated. If
the torch is removed from the workpiece, the pilot
arc will automatically restart if the torch switch is still
pressed.
Indicator Meaning
D26
Torch Switch Enable - When ON
(start) indicates torch switch is
pressed.
D25
CD Enable - Initiates spark gap on
CD PC Board. Indicator should
come ON then go OFF after a pilot
arc has been established.
D65
CSR - Indicates main cutting arc is
established.
D47
AC OK - When ON indicates that AC
Input voltage is okay.
D31
Drag - When ON indicates that the
torch tip is making contact with the
workpiece.
Logic P C B oard
B. CD (Capacitive Discharge) PC Board
Functions
NOTE
Refer to Appendix 7 for CD PC Board layout.
The CD Board functions are initiated by the CD En-
able signal from the Logic PC Board. The CD arc
starting circuit fires the spark gap producing the high
voltage spark which starts the DC pilot arc. When a
pilot arc is sensed by the Gate Drive Board, the PSR
signal shuts off the CD enable.
C. Gate Drive PC Board Functions
NOTE
Refer to Appendix 5 for Gate Drive PC Board lay-
out.
The Gate Drive Board controls the amount of time
the FETs are turned on. This is done with a pulse
width modulator (PWM) controlled by the demand
signal from the Logic PC Board. The longer the FETs
are on, the more output current. If a short develops,
the primary overcurrent will shut down the gate drive
and not allow the power supply to power up and
run.
The PSR signal senses any current in the secondary
and determines what the PWM should do for a pulse
width. If there is current in the secondary, the PSR
signal will go back to the Logic PC Board and shut
off the CD Enable signal.