The voltage that the THC is looking at is the voltage between the negative electrode and the positive work ground connection. If you are cutting at a constant speed and at a constant height (level plate, THC voltage control off)....then this voltage will remain relatively constant. I suggest that you verify that by doing a straight cut on level plate. You can also check accuracy by measuring the actual voltage at the Raw arc voltage connection with a digital voltmeter and compare that with your digital readout....they should be pretty close to the same.
When the torch is raised (while cutting at a constant speed) you will see the voltage rise....this is because the arc gets longer. So....if you height control is causing the torch to oscilate up and down....expect to see the voltage rising and lowering. I'm sure CandCNC can help you with settings that will eliminate the oscilation....often has to do with gain or z axis speed settings.
Other things that can affect arc voltage (I don't like to call it tip voltage....as 1. Hypertherm plasma systems do not have a part called a tip, and 2. On plasma systems that have a part called a tip....it is the nozzle....which is not where the voltage is measured. The measurement is from the electode to the plate.:
- If there are large amounts of water in the air....it changes the resistance of the plasma arc, which will change the height/voltage relationship. This is unlikely in your case.
- A loose or dirty work clamp connection. Generally if you have clamped directly on the plate you have eliminated this issue.
- Consumables that are at the end of their life will generally cause the voltage to increase....and the torch will dive into the plate , but will not oscillate.
I suggest the problem is with a setting in your software that controls the z axis while in arc voltage control mode.....not in the plasma system.
Jim Colt Hypertherm