If your Powermax900 even has the arc transfer output (it was an optional board), it is a contact closure that remains closed while the arc is transferred to the metal. It actually operates by sensing current (amperage) on the work cable. When the arc goes out, there is no current.....and the contact opens.
Funny on the warranty! The nice thing is that you have a 12 year old plasma that still cuts well.....and is still supported by the manufacturer! If you look around at other brands (other than Hypertherm) you will not se that very often!