From: gherold@teachspin.com   
      
   On Monday, January 29, 2018 at 1:15:10 PM UTC-5, et...@whidbey.com wrote:   
   > Reecently I helped a neighbor connect a Chinese made CNC plasma table   
   > to an American made plasma cutter. After I figured out that the   
   > "partial pressure" the Chinese manual mentioned was in reference to a   
   > built in jumper selectable voltage divider  I was able to get the two   
   > machines talking to each other and everything works now. But the   
   > Chinese manual shows a filter on  a sense wire and I don't know   
   > exactly what to do about it. The sense wire is connected to the copper   
   > shield on the plasma torch and to a terminal in the CNC control. The   
   > machine uses the shield to sense the work. The machine moves the   
   > plasma torch down until the shield contacts the work and then moves   
   > away a set amount and energizes the plasma torch. I think, but am not   
   > sure, that the control can now sense the distance between the work and   
   > the torch tip, so that if the work is warped and rises or falls the   
   > torch will follow the contour of the work. In any case, the connection   
   > diagram for this sense shows it being wrapped a few times through a   
   > ring. And somehow the manual alludes to this ring as being some sort   
   > of filter. Since the neighbor didn't have any type of ferrite rings I   
   > just wrapped a few turns of the sense wire through a few insulated   
   > washers just to see if I could get the machine to work. And it did.   
   > Well, I dug  a ferrite ring out of a bad switching power supply and   
   > removed the coiled wire from it. I'm hoping I can just duplicate the   
   > washers trick with the ferrite ring but I'm thinking that I need   
   > advice on how many turns of wire through the ring I should use. I   
   > know, there are many different types of ferrite and I have no idea   
   > what kind mine is. And there must be a bunch of other variables as   
   > well. But if I can at least not ruin anything it would be great.   
   > Thanks,   
   > Eric   
      
   Cute trick using some steel washers.  If the signal line is coax, or   
   twisted pair, or something else with a shield, then you are making a   
   common mode choke.   If a single wire then it's just a choke.  Regardless of   
   which it's kinda hard to say how many turns you'll need.   The impedance   
   of the choke is working against some other impedance in the circuit.  I   
   typically do what you did.. wrap a few turns and see if it works.  If   
   you've got a 'scope, you might be able to look at the signal line and see   
   the noise and reduction... but all sorts of caveat's here about floating   
   AC loads and HV.  You don't want to blow out your 'scope.   
      
   George H.   
      
   --- SoupGate-Win32 v1.05   
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