THEORY OF OPERATION
FIGURE E.5 – PLASMA OUTPUT SECTION AND TORCH
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INPUT 115/230/1/50/60 VAC
L1 SW1 A 300uH
B |
RL3 |
| RL2 |
R1 |
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10/10W |
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F1 |
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1A/250V | RL2 | |
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C26
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CP | CP | CP | |
CP | CP | ||
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AC | AC |
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R1 
CP
R2 
15K/3W 15K/3W
1500uF/250V
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C1a,b
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C2a,b
Q1a,b,c | D10 | Lout | BS1 |
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IRG4BC30W | WRK | |||
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T2 | SEC |
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PRI |
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C12 | D11 |
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WORK CLAMP
Return
V1 |
RL2
RL1
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Q2a,b,c | 6.8k/5W |
IRG4BC30W |
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FN1 | 230VAC | V2 |
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115VAC
L1
T1
230V
RL1
1500uF/250V
| SHUNT | EL (3) | |
C13 | SH- | SH+ |
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NO | COM | NC |
Purge Switch
115V
L1
Input
Voltage Board
12VDC
Air
Solenoid
1
CN1 | 15VAC |
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2 | 15VAC |
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3 | SAFETY |
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4 | +28VDC |
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5 | SEC GND |
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6 | OVLOAD |
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7 | 115/230 |
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8 | +12VDC |
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| 11 4 | 13 7 | 19 24 21 23 8 | 17 | 1 | 2 | 3 | |||||||
| PS2 | PS1 | SEC GND OVLOAD | SAFETY | V+ EV1 +15Vrms | +12VDC | +8V SW +12VDC SW | SEC GND | OVLOAD | TRANSFER SW | TRANSFER | SOL 1 DRIVER | V OUT OUTPUT TRIGGER SOL 2 DRIVER |
| POT WIPER | POT CW | POT CCW |
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CN1 | 8 | 6 | 17 9 | 3 | 1 | 2 | 18 14 7 | 15 4 | 11 5 | 16 10 12 13 |
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Display LED's
Output Control
Control Board
PT
12VDC Solenoid 2
OUTPUT SECTION AND TORCH
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The output section contains a relay which, upon receiving a pilot signal from the control board will enable the operation of a pilot arc or a cutting arc. The printed circuit board mounted current sensor regulates the pilot and cutting current. The output choke, which is in series with both the pilot circuit and the cutting circuit, provides current filtering to enhance arc stabil- ity.
The PCT 20 torch uses a patented touch start mecha- nism that provides superior starting performance over other touch start systems. The torch head consists of 3 major parts: torch body, insulator and piston. The insulator provides an electrical barrier between the piston and torch body. The piston provides a path for electrical current to the electrode. The piston also dri- ves the electrode to the nozzle for arc initiation. The torch body contains the main torch components: the trigger, pilot arc, cutting arc, and air flow systems are included. See Figure F.10 & G Section for more detail.
A copper nozzle with a patented internal swirl is used to focus the arc. A small, precise hole in the end of the nozzle constricts the arc and increases the current density. As the air enters the torch head, it is directed
between the electrode and nozzle for maximum elec- trode cooling. A portion of the cooling air exits in the chamber through vents in the side of the nozzle. A swirl texture located inside the bottom of the nozzle increases the plenum air swirl strength, and improves arc start reliability and
Plasma arc initiation occurs as follows: First, in the idle state, a spring inside the torch head pushes the piston and electrode forward to make continuity with the noz- zle. When the trigger is pulled, air flow begins and cre- ates enough back force on the electrode to overcome the force of the spring. However, the solenoid valve allows enough forward force on the piston to maintain continuity between the consumables. After this continuity has been verified, output current is estab- lished and regulated. Once the current stabilizes, the solenoid valve turns off, removing the forward force on the piston. The back pressure drives the piston and electrode away from the nozzle, creating the plasma arc. The air stream forces the arc out the orifice of the nozzle. This appears as a pilot arc, which can then be transferred for cutting.