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| THEORY OF OPERATION |
OUTPUT RECTIFICATION AND FEEDBACK CONTROL
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| POLARITY |
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| BOARD | ||
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| SWITCH |
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| WORK | ||
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| TRANSFORMER |
LINE |
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| ELECTRODE |
MAIN |
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SWITCH |
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TRANSFORMER |
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R | X2 |
| AC | DC+ |
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E |
| SHUNT |
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| SCR |
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C |
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| BRIDGE |
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O |
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N |
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N |
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E | X1 |
| AC | DC- |
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C |
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| CHOKE |
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T |
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| SIGNALSGATE |
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POWER |
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| FEEDBACK | |
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FACTOR |
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CAPACITORS |
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| ARC START |
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| LCD DISPLAY | |
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| 115VAC | PROTECTION | 115 VAC | CONTROL | KEYPAD | |||
FAN |
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| SNUBBER |
| GATE SIGNALS | BOARD |
| LED | ||
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| KEYPAD | |
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| 115 VAC |
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| 115 |
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| VAC |
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| 24 VAC |
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| CONTROL | 18 VAC |
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| 115 VAC |
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| TRANSFORMER |
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| 16 VAC |
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RECEPTACLE |
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| 115 VAC |
| HIGH VOLTAGE | HIGH FREQUENCY SPARK | |||
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| REMOTE |
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| CIRCUIT |
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| RECEPTACLE |
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The AC output from the main transformer secondary is rectified and controlled through the SCR bridge. Output current is sensed at the shunt, as a low volt- age signal, and fed back to the control board. The control board compares the commands of the keypad (or remote control) with the shunt feedback signal. The appropriate gate firing pulses are generated by
the control board and applied to the SCR bridge through the protection / snubber board. The control board controls the firing of the SCRs, thus controlling the output of the machine. See SCR Operation. The control board also powers and commands the keypad LED board and the display board.