Cebora PLASMA PROF 123 ACC Service Manual page 6

CEBORA S.p.A.
The control board (47) receives the temperature signals originating from the thermostats
placed on the transformer (37) and on the igbt module dissipater on the power board (56).
According to these over-temperature signals, the Power Source is stopped and the corresponding
error code is displayed on the operator panel.
The sensor board (52) works as an interface to the Power Source output, it receives and
conditions disturbed signals originating from the system critical areas.
These signals are:
- HF board (27) command;
- Power Source output voltage;
- pilot arc voltage.
The Power Source output voltage signal, received through the HF-filter board (32), is filtered
and converted into PWM type signal, on the sensor board (52) and then sent to the control board
(47) where it is used to check the cutting condition.
The HF board (27), combined with the HF transformer (50), generates the high voltage and
high frequency pulses to the torch electrode and nozzle terminals, needed to start the pilot arc.
Its operation is conditioned by the Power Source output voltage value, detected between the
output positive pole of the Power Source (nozzle potential, downstream of resistor (33),when
contactor (55) is closed) and the common point between choke (35) and HF transformer (50)
(electrode potential). With a voltage higher than 200 Vdc the circuit generates high voltage and
high frequency pulses; with a lower voltage the circuit stops working.
This system is based on the system according to which under no load condition the Power
Source output voltage is maximum, approximately 280 Vdc, while with pilot arc or transfer arc
the voltage depends on the working conditions (current level, material to be cut, type of gas etc.),
therefore considerably lower than 200 Vdc (150 Vdc approximately with pilot arc on).
The pilot arc has a 2,5 s. maximum length; after this time if the cutting operation does not
start, e.g. the control board (47) has not received from the power board (56) the signals to cause
switching into transfer arc, the pilot arc halts until it receives the next start command.
The HF-filter board (32) is extremely important because it prevents the HF pulse from going
back to the Power Source thus damaging other components. Therefore, during maintenance
operations make sure that this board is always correctly connected to the original terminals,
before activating start-up with HF.
The signals processed by the electronic boards and present at its connectors are listed in the
table in chapter five .
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12/04/2012