Tweco 300 XT Auto-Cut 400V - Manual (Page 129)

AUTO-CUT 300 XT
Manual 0-5290 APPENDIX A-47
• Cut current set too low for torch parts being used. Pilot current is set based on cut current. If cut current
is too low pilot current will be lower and may not transfer at the height used for higher current consum-
ables.
• Preflow pressure/flow too low.
• Remote Analog Current Control switches set wrong can also result in lower than normal pilot current
setting. See section on these switch settings under section for code 104.
• Defective work lead current sensor circuit. If transfer is not sensed cut current remains at the lower start-
ing level and pilot timer (85 ms. or 3 sec) will time out.
107 Not Used. This is one of the reserved codes from the earlier product.
108 Tip to Electrode Voltage Fault
The Pilot voltage, measured between tip and electrode varies with different current and gas type, flow rate and
consumable design.
Once the arc is transferred the pilot switch opens leaving the tip basically floating. The voltage then is deter-
mined by how much of a cold gas barrier surrounds the arc. Too much current or too little gas and the arc
starts to contact the tip reducing the voltage difference between tip and electrode and leading to a double arc
that destroys the consumables.
The CCM measures both electrode and tip voltage and calculates the difference. If the difference between tip
and electrode is found to be less than a minimum voltage we stop cutting and set a fault for the 108 code. The
normal tip to electrode voltage is different for different processes so the min value for each process is embedded
in the cut charts when using the DFC 3000 or in the CCM code if using the GCM 2010 or for Auto-Cut XT gas
controls (GCM 1000XT or the built in one in the AC 200 XT).
New for the Auto-Cut XT units is a switch on the rear of the power supply that needs to be set according to the
plasma gas. If using an oxidizing gas (O2 or Air) set it as indicated for those gasses (left if AC 200 XT or up for
AC300XT) or if using a non-oxidizing gas (N2, H35 or other inert gas) set it to the right or down as indicated for
those gas types.. This switch adjusts the range of voltage for the gas type to better protect the torch. A wrong
setting could result in false setting of the 108 code.
During piloting and ramping (the time from transfer until the current reaches full cut current), we lower the
allowed tip to electrode voltage to about 80% of that allowed during cutting because the current is lower and
the gas flow is lower during that time.
Causes for 108 code:
• Gas Flow/pressure too low for consumable parts being used.
o If gas source pressure is not well regulated it is possible pressure may be OK at times and drop too
low at other times such as during a cut.
o A leak of the preflow/plasma gas after the pressure/flow control (GCM 2010, DPC, GCM 1000 XT)
can reduce the pressure/flow to the torch because some if it is bypassing the torch, while seeming to
have enough pressure/flow at the gas control.
• Cut current set too high for consumable parts being used.
• With DFC 3000 a faulty component would be expected to set a fault code in either the DPC or DMC.
However, if a wrong process is selected which doesn’t match the consumable type or if using a custom
process where pressure has been set too low or current too high that could cause 108 without setting any
faults in the DFC 3000.
• A broken pilot wire in the torch lead making intermittent contact can allow piloting or sometimes the
torch can transfer using only HF (high frequency). This intermittent connection will upset the tip voltage
measurement and can result in the 108 code. Symptom is - it may cut for a short time then fault. Check
for an open/broken torch lead pilot wire.
• Physically shorted torch body between anode (tip) and cathode (electrode).
The fault resulting in a 108 code is measured while cutting. It is more likely a shorted torch body, depending
on the resistance of the short, it will set code 208 (Unwanted Current) as that is measured prior to starting cut
However, it must be considered as a last resort.