ESAB LHF 405 PIPEWELD, Руководство по обслуживанию

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Edition 071024
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LH20/1:3 Functional control circuit ANTISTICK, HOTSTART, ARCFORCE
The ANTISTICK function is carried out by the circuit made of the A3 IC and the
transistor V31. If the output voltage falls down below the ANTISTICK threshold,
transistor V31 switches on, consequently switches off the output transistor of the
A3b comparator and the output transistor of the A3a comparator switches on. It
pulls down the current setting signal on the A5b non--inverting input to the minimum
value, and consequently, it limits the output current of the power supply. In MMA
mode operation of ANTISTICK is delayed by C17, R36, R37, R38 and R39. In TIG
mode ANTISTICK operates without any delay while in AAG mode ANTISTICK is
turned off.
The HOT START function is carried out by the circuit made of the A4 and D1 ICs.
When the welding starts and the arc is stroke, the +15V signal shows up on the
non--inverting input of the A4a. The capacitor C16 is charged via resistor R21 and
the potentiometer of the HOT START time setting. Time required for charging the
C16 up to +10,7V is the time of the HOT START. Untill the voltage on the C60 is
lower than 10,7V, there is a high level on the A4b output, and the output transistor
of the D1b connects resistor R27 to the ground. It causes the approximately 35%
voltage rise on the A5a output compared to inverting input thus increasing the
welding current value. In TIG mode the HOT START is disabled by A6c.
The ARC FORCE function is carried out by the circuit made of the A5a operational
amplifier. As the machine output voltage crosses the ARC FORCE threshold and
keeps decreasing, otput voltage of A5a also decreases. Consequently, the voltage
on the slider of the R03 potentiometer decreases, voltage on the A5a output
increases, thus increasing the welding current. The max current increment caused
by the arc shortening, may be adjusted by means of the R03. In TIG mode the
ARC FORCE is disabled by D2a.