Torch height control is the single most important aspect of any cnc plasma cutting system...if you are concerned with cut quality and consumable parts life. A properly designed plasma height control system must work in conjunction with the cnc control as well as the part program in order to achieve the correct pierce height, pierce delay time, cut height, and must have the means to ignore voltage anomalies caused by kerf crosssing as well as machine slowdowns due to cornering and fine feature cutting.
All industrial quality (read more robust, more expensive) cnc plasma machines have full featured , well designed height control systems.....you cannot buy one of thes machines without height control. Unfortunately...many of the low cost, entry level cnc plasma machines that are designed for hobbyist or small shop applications offer height control as an option....which allows these machine builders to offer their products at lower prices. It is not a good idea to buy a cnc plasma cutter without height control....it will not cut as well and it will eat up consumables....resulting in higher cutting costs as well as poor cut quality.
A basic height control will automatically locate the surface of the material to be cut, will retract to a user set pierce height (always higher than the best cut height), will then fire the torch at the pierce height and remain in place for a pierce delay time (to allow full plate penetration before the cut starts), then will index down to the torch manufacturers recommended cut height. Once the x and y axis get to the programmed best cut speed....an arc voltage feedback control takes over the real time control of torch to work distance by monitoring arc voltage (as measured from the torch electrode to the plate), and adjusting very accurately in order to maintain the correct torch to work distance. The cnc has to be able to "freeze" the arc voltage control during normal corner slowdown and kerf crossings, as well as at the end of the cut when the arc extinguishes...this height freeze is to prevent torch diving. More sophisticated height controls also have the ability to auto - calibrate torch to work distance to compensate for normal consumable parts wear....thus ensuring that cut quality will remain constant throughout the life of a set of torch consumables.
A typical plasma height control system consists of a z axis motorized slide with mounting configuration for the plasma torch, a voltage divider /isolator circuit (to reduce the DC arc voltage signal and filter it to a usable level), an electronic control box that monitors the input, output (from CNC and plasma, and voltage divider), as well as associated cables and user interface panel. Some height control systems are "standalone" (will work with any plasma/cnc machine configuration) and some are integrated (designed to operate as an additional axis of the cnc machine.....and is operable through the motion control system software.
They are typically a fairly high price addition to an entry level cnc machine.....but make the system cut like a cnc machine should.....in a hands off automated manner.
The unit listed on the initial post appears to be just the arc voltage control circuitry.....you would still have to design an initial surface sensing process, the ability to retract to pierce height, a pierce delay timer...a motorized z axiss assembly to raise/lower the torch, etc. Sounds like some engineering and design and testing would certainly be involved to make this system work.
Jim Colt Hypertherm