ESAB Cadd Tig 1500i TA34, Service Manual

Page: 29 / 50

S0740 800 186/E080826/P50
-- 29 --
ct34_20
20AP1:7 Arc voltage feedback
This circuit measures and scales the arc voltage to a suitable level for the
processor. 64 V arc voltage produces a voltage signal of 5.0 V at the cathode
of diode D13.
Open--circuit voltage control
Version 1 of 20AP1:
The open--circuit voltage control holds the voltage at about 70 V.
Version 2 of 20AP1:
The open--circuit voltage control holds the voltage at 46 -- 60 V.
When the VRD (Voltage Reduction Device) function is active, the open--circuit
voltage is < 35 V (19 -- 26 V). The VRD function can only be activated or
deactivated by the ESAT, see page 37.
Note! Spare part boards are delivered with the VRD function deactivated.
See the component positions diagram on page 32 for identification of circuit
board versions.
TIG
The open--circuit voltage is about 90 V. Arc voltages above 45 V are defined
as no welding.
Output voltage is produced only when TIG welding is in progress. If the
open--circuit voltage/arc voltage is above 45 V for more than 100 milliseconds
the open--circuit voltage control is activated and then the output voltage is shut
down.
MMA
S
The machine generates the actual open--circuit voltage, see: “Open--circuit
voltage control” above.
S
Touch the electrode on to the workpiece. When the open--circuit voltage
goes below 45 V (16 V when VRD is active), the open--circuit voltage
control is disabled.
S
When the current exceeds 8 A the hot start current is activated.
S
When the arc voltage exceeds 52 V, welding stops and the open--circuit
voltage control is activated.
20AP1:8 TIG functions
LiftArc TIG start
S
Touch the electrode on to the workpiece.
S
Press the torch trigger. The machine produces a current of about 6 A.
S
Lift the electrode from the workpiece. The arc strikes and the current
increases to 30 A.
S
When the arc voltage exceeds 8 V, the current increases / decreases to
the set current.