New Source of Communication Issues

[Steve Wonser]

I discovered the source of a communication problem between my computer and my ShopBot Desktop that is related to electromagnetic interference (EMI). It's something that I never really thought about.

I have a vacuum pump that I built years ago for veneering and to use as a vacuum hold down on my lathe. I decided to use it for hold down on my ShopBot Desktop. What I discovered is that I was getting communication errors while using the vacuum. The computer would intermittently loose communication with the ShopBot, even when it wasn't cutting anything.

I have my ShopBot and control computer on a separate electrical circuit that has a surge suppressor and noise filter on it so I didn't think that could be the issue. After looking at the ShopBot diagnostic information and not seeing anything unusual I took a shot in the dark and moved the vacuum pump away from the computer. That fixed it. In retrospect I probably couldn't have chosen a worse place for the vacuum, which was directly under the computer. I've posted a picture of it.

The lesson learned is to be aware of not only the electrical connections to the computer and ShopBot but also electrical motors that may be running near them.

[scottp55]

Thanks Steve,
Almost ready to place my Vac pump into my MakerCrate and hadn't even considered that:(
Timely!
Think that may have been source of comm problems you were having?

[Steve Wonser]

No, in fact I'm still getting them occasionally when cutting something with a lot of small movements. Luckily I know how to recover now. I just need to plan for it and make sure that I don't carve away my Z-Zero point.

[Burkhardt]

I would not bet that it is the actual vicinity of the pump but rather the way it is wired in general and specially how all the system elements are grounded. I suppose it is the little rocker piston pump under the PC? These have normally an induction motor without sparking brushes and should not create much if any EMI while running (if you are cycling it on and off that is a different story). I have a similar one running maybe 20" away from my laptop without trouble. For that matter you don't have by chance the Shopbot controlling the vacuum pump?

That said, while I don't have a Shopbut, my USB controller gave me regular communication errors or wild bit excursions until at some point I found a missing ground wire of the controller board itself. With the laptop hanging on it, the whole system acted like a big antenna picking up all possible noise from DC, pumps, steppers and the spindle VFD. Wire fixed, problem fixed. I just mention it to say that it sometimes takes only a small change to create or fix such problems and any of them may be slightly different. Especially ground loops can be nasty (like grounded PC -> USB cable -> CNC machine on separate ground). The "good" quality double shielded USB cables with fat ferrite beads may help or sometime make it worse.