Tweco 15XC Merlin - Manual (Page 90)

CUSTOMER/OPERATOR SERVICE 5-18 Manual 0-2251
5.10 TROUBLESHOOTING THEORY (continued)
Switching Control Board
(continued)
Logic Board Functions
LED/Current Control Board
Remote Control
passes the E-Stop function of the remote. The switching
control PC board also routes the shunt amp output to the
digital ammeter in the remote. CSR (current greater than
25A) and over-current shutdown (greater than 175A)
signals are sent to the logic PC board.
The logic PC board controls the timing and sequencing of
the system. It monitors the pressure, temperature, and
flow interlocks and controls the gas flow in run, set, and
purge modes by turning on the plasma and secondary
solenoids. The logic PC board also controls pre-flow and
post-flow durations, which are selectable by DIP switches
on the board (see Figure 4-G). The logic board drives the
sequence status LED indicators and contains the circuit for
measuring coolant conductivity.
The logic board receives either a latched start signal from
the remote control panel or a non-latching start signal from
the hand torch switch or remote pendant. Both latching
and non-latching signals are available from CNC devices.
The logic PC board then initiates gas pre-flow and ener-
gizes the main contactor W1 or W2 (as directed by the
voltage selection PC board). The logic board then enables
the PWM switching control circuit. The logic board imme-
diately activates the pilot contactor to initiate the pilot arc.
As soon as the pilot arc (constant DC current) is estab-
lished, the PSR relay shuts off the high frequency. The
logic board supplies ‘OK-to-move’ contacts, which close
when main arc transfer has occurred and pilot has shut off.
A second ‘OK-to-move’ contact is wired to control an
optional high-flow water shield.
The LED and current control PC board contains the
sequence status LED indicators and the front panel current
control pot.
The remote control unit contains the several system control
functions. Momentary start and stop switches control
system operation and the main current control pot controls
cutting current output. A digital ammeter displays a
preview of the main current setting (or corner slowdown
setting) before starting the cut and displays actual cutting
current after arc transfer. A behind-the-panel control sets
corner slowdown current reduction and an emergency
stop switch shuts off the power supply's main contactors,
gases, and coolant system. CNC interface connectors and
the power supply remote cable connection are located on
the rear panel of the remote.