3 ms·
IIRC, the arc voltage was proportional to height only at constant velocity. I guess it was also a function of how much material is below the arc at the instant.
by fest 10y ago
IIRC, the arc voltage was proportional to height only at constant velocity. I guess it was also a function of how much material is below the arc at the instant.
I was working on a controller which was supposed to get it's setpoint by measuring voltage during first few seconds of a cut, but the project turned out to be outside of my EE skills at the time (isolating analog signals, high voltage resistive dividers that didn't blow up because I had no low-voltage feedback signal from plasma source etc.)
About the need for rapid accelerations- that too was one of the things we learned by building this machine. IMO it should be stressed more in discussions about plasma cutters.
In this case the blue linear slide actuator was off-the-shelf part and modifying it would require to cover the belt and linear guides inside with something else and was thought to be too much of an effort.
- jacquesm 10y agoYou can usually tap a point in the plasma cutter power unit that will tell you exactly what the arc voltage is, almost any slightly larger plasma cutter power supply will have a point that's convenient. You'll still need to use an opto-coupler, the way I built mine was the setpoint and comparator lived on one side of the divide, then two input bits, one for 0.1 V below the setpoint or lower, -0.1 to 0.1 was both inputs off and one for 0.1 V or higher, the setpoint was scaled so that it would have a nice range mapped to the inputs of two op-amps doing the comparison. The outputs of those op-amps drove the opto couplers and the software would track the 'Z' stepper up, down or hold depending on those two inputs. Super simple really.