Sorry for the long readā¦
Ground loops make these machinesā electronics very susceptible to both radiated & conducted noise usually from the anode HV side of the LPS. That is why typically these problems are a combination of the LPS arching or emitting corona and/or poor grounding design.
The cathode side is usually not a source as it should be at ground potential and the max current is in the MA range.
Long ground wires or long input wires to low voltage electronics especially in poorly grounded systems can result in dynamic ground shifts that are interpreted as resets and other false control signals. In a CO2 laser machine, the presence of 10ās of thousands of volts and 3.3vdc electronics make this a HARSH environment.
Donāt think of ground wires as simple DC returns of current. Rather think of them as active transmission lines with inductance and capacitance. That means that high-speed changes in current with enough energy can shift the ground for ns.
In the case of radiated problems think of wires as antennas where enough wire, placed close enough to the emitter, when combined with poor grounds, can shift the level of a signalā¦
These problems are hard to fix because of their dynamic nature and because they relate to problematic physical characteristics and layouts i.e. wire length, size, fastening, and placement.
Ugly ratās nest wiring often also means poor grounding designs which are susceptible to noise.
The above does not directly tell you how to fix this problem it is intended to give you some background to use while you hunt for the problem.
Try these simple things first:
- Disconnect the USB cable going to a PC and see if the problem is still present.
- You can turn out the lights and look for corona around the LPS its wiring and HV connectors.
- I would add a wire from the L- to a purposeful bolt in the frame. L- is the cathode return that comes from your laser current meter. That current should already be tied to the frame through the LPS frameā¦ but who knows. Use this same bolt as your common return for the DC supplies.
- Tie a short-as-possible beefy wire directly from each supplies ground to that same lug using ringtones that are soldered. Fasten ring tongues to the bolt with star washers on either side. Do not daisy chain these grounds.
- Reroute signal wires as far from the anode wiring as you can
Below are some guidelines for grounding that I have used building these machines extracted from Don's Laser Things: Battling Electrical Noise in CNC builds
You probably cannot do much about #1 other than ensure input wires are as short as possible. Focus on 2-5 first. If that does not resolve the problem then you may have to start moving things and experimenting with the layout until you find the source.
My experience has been that these problems first manifest themselves as mysterious radiated noise but end up being solved by better grounding.
Grounding Design:
- The ground system design must consider the path the current follows to get back to the source driver (thatās usually the device on the PCB). Signals that are a long way away that are not grounded back to the source can experience ground shifts when exposed to strong transients due to line inductance, capacitive coupling, voltage drop, etc. The distance that the current has to travel can have a profound effect on the signal voltage seen at the receiving end of the wire. As an example, if a switch out on the gantry uses one signal wire but the return is tied to the frame out on the gantry, the return current has to flow through the frame back to the controllerās ground connection then across the PCB and to the input receivers ground connection. Unless the frame of the gantry has a beefy wire running back to the controller the ground path may not exist at all or at best travel through moving ball bearings. In unknown paths like this who knows what voltage is dropped across what unexpected resistances/inductances.
- Power supply wiring should be designed just like signal wiring. Power supplies should be wired directly to their load. That means two beefy wires (power and ground) as short as possible directly to each load. The bigger the wire the better, size matters here. Do not run a PSās wiring to one load and then daisy chain the grounds to the others. Each supply has dedicated power and ground wires to the load.
- Ground each power supply back at the supplyās terminal with an additional wire run to a common gas-tight connection on a common frame location. Yes, I mean a single lug that all PS ground lugs connect to. All supplies should literally have a beefy wire from the ground lug on the supply to the common frame lug.
- Tie the safety ground from the AC plug to this same common lug. In weird conditions, I have found that isolating frame ground from PS ground to solve some noise problems. Try this only as a last resort.
- For the common ground, I use a bolt with soldered ring tongues stacked with star washers in between each lug.