Poor connection to the workpiece causes the voltage to not operate within the range on the chart. (takes more voltage to get the proper current density). ALWAYS clamp the workclamp to the material. If you don't hold the 1/16th recommended arc gap then your cut flair will increase and cut quality suffers. When the voltage climbs outside the percentage you have set on the Tip Saver (anti-dive) then it locks any DOWN movement. Once the voltage spirals out of the proper range it's hard to get it to adjust itself back. The DTHC will hold better than 1 V (it has a settable "Span" value from as low as 1/4 volts to several volts). of arc volts while cutting. The two most important indicators (besides torch volts) are UP and DOWN. Since the DTHC signals MACH to raise or lower the Z (similar to an external jog command) the signals displayed on the screen are important to analyze what is happening. If the UP is on the Z SHOULD be moving UP. Conversely if DOWN is on it should move down. If you are not getting a DOWN indicator if the voltage climbs above the Preset then either the TIP SAVER has cut in or the communications between MACH and the DTHC are not working. The DTHC has a self test that will let you quickly confirm you have all the proper signals.

If you setup and cut a line with the tip at .063 above the material and at the recommended optimum feedrate with the THC Button OFF in MACH you can observe what the DTHC is doing. The voltage should be close to the chart voltage for that material and nozzle. If it is not then you have physical problems with the plasma. The voltage is your "altitude" reading. If it's off then so will be your cut. As it cuts manually observe the Torch Volts reading; it will change but if the material is flat and the cut is a straight line it should not change more than a few volts.

The other common mistake I see a lot is the THC Corrections (settings tab) gets "adjusted". The numbers are the absolute Z values it will allow (Max and Min) as it cuts. They are defaulted to +1 and -1. If you are running in INCHES units then that basically turns it off. If you happen to be using MM it prevents any movement at all. Set both to 0 and you get no adjustment at all. Set the MIN to high and it will just ratchet up the torch evn though the poor DTHC is screaming "MOVE DOWN, MOVE DOWN"

The last thing is about Grounding. The table needs to have a solid earth ground (ground rod). The workclamp out of a plasma is not ground and does not ground the table. If the table is floating then it can be a hundred volts above a true earth ground. Grounding the table is not only for safety but to keep the nasty noise off the table structure and from being transmitted back down wires to the control electronics.

We got to great lengths to keep the low voltage control signals totally isolated from the noisy plasma. If the noise is enough to be inductively coupled across or radiated through the air it defeats the isolation we designed in.

TOM caudle
www.CandCNC.com