Cebora PLASMA PROF 80 Service Manual page 5

CEBORA S.p.A.
checking the signals originating from the pressure switch (35), thermostat in the transformer (50)
and reed sensor (14) on the protection of the central adapter (12).
The pressure switch (35) inserted on the plasma gas line stops the power source and lights the
led (L) when the pressure falls below the minimum permitted value.
The thermostat on one winding of the transformer (50) stops the power source and lights the
led (G) when the temperature of the transformer (50) is too high.
The setting board (19) makes up the actual system regulator.
It generates the drive signals for the rectifier bridge scr on the power board (20), based on a
comparison between the current reference signal originating from the control board (9) and the
current feed-back signal originating from the transducer (34).
The HF board (25), combined with the HF transformer (23), generates the high voltage and
high frequency pulses needed to start the pilot arc. Its operation is controlled by the setting board
(19) and is subject to the presence of alternating voltage on terminals J4 and J5 of power board
(20), provided by a specific secondary winding of the transformer (50).
Near the output terminals of the power source is the HF-filter board (22), which serves to
prevent the high voltage and high frequency pulses generated by the HF transformer (23) from
travelling along the wiring into the power source, where they would cause malfunctions or
errors. Therefore, during maintenance operations, make sure that this board is always firmly
connected to the original terminals before striking the arc.
The power outputs of the power source, to which the torch is connected, are gathered into the
central adapter (12) on the front panel. This is a multiple connector that incorporates a power
socket for the torch electrode, two contacts for the torch nozzle, two contacts for the start button,
four contacts for torch type recognition, and a pneumatic socket for the plasma gas. This central
adapter is fitted with a protective hood; the reed switch (14) mounted on the panel board detects
its presence, and prevents the power source from running if the hood is missing.
When the start button is pressed, the control board (9) strikes the pilot arc by activating the
solenoid valve EL1 (37) (the one with the flow reducer), the nozzle relay RL1 on relay board
(27), produces output voltage on the power board (20) and high frequency. With the contact of
nozzle relay RL1 on relay board (27) closed, the positive voltage on J2 of power board (20) is
applied to the torch nozzle through the 1.3 ohm resistor (38).
When the pilot arc is lit, you have approximately 2 seconds to begin cutting, after which timer
the pilot arc shuts off until the start button is pressed again.
When the torch with lit pilot arc is placed near the workpiece, the arc current begins
circulating on the earth conductor due to the potential difference caused by the resistors (38).
The solenoid with reed bulb (26) detects this arc current and provides information about it to
the control board (9), which begins operation in transfer arc. Thus it controls solenoid valve EL2
(37) (the one without flow reducer), opens the contact of nozzle relay RL1 on relay board (27)
(to allow the torch to function properly and control the actual cutting current), and switches the
current reference signal from the pilot arc level to transfer arc (cutting) level based on the setting
of knob (M).
When cutting ends, output voltage is no longer output, the solenoid valve EL2 (37) is
disengaged, while EL1 (37) remains powered for the post-gas time (approximately 90 seconds).
The signals processed by the electronic boards and present at their connectors are listed in the
tables in chapter five of this manual.
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25/06/04