ESAB Arc 4000i Service Manual page 39

Methods of measuring the arc voltage
Various methods of measurement are available by transferring a link between
contacts Y1, Y2 and Y3. When delivered, the link is fitted between Y2 and Y3.
The link must be connected between Y2 and Y3 for MMA and TIG welding.
Welding with the filler wire positive: voltage sensing from the wire.
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This is the commonest arrangement for MIG welding.
Y2 -- Y3 must be linked. This method of measurement allows for the
voltage drop in the supply conductor (= to the welding gun). The input
signal is measured between inputs X1 and W2. Amplifier IC8:14 is active.
Welding with the filler wire negative: voltage sensing from the wire
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Y2 -- Y3 must be linked. This method of measurement allows for the
voltage drop in the supply conductor. The input signal is measured
between inputs X1 and W5. Amplifier IC8:8 is active.
Welding with the filler wire positive or negative, without external
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sensing from the wire or workpiece.
Y2 -- Y3 must be linked. The input signal is measured between inputs W5
and W2 (= the voltage at the power source terminals), as there is no
connection to X1. Amplifier IC8:14 is active.
Welding with the filler wire positive: voltage sensing from the wire
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and workpiece.
Y1 and Y2 must be linked. This method allows for the voltage drop in both
the supply and return conductors. The input signal is measured between
X1 and X3. Amplifier IC8:14 is active.
Note: If the voltage signal connection to X3 is lost, the power source loses
control of the arc voltage.
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S0740 800 191/E080229/P78