High frequency absorbers

[sihaam]

Hi All
I build a XY Tables for High frequency plasma cutters. However the HF start causes EMF surges which tend to interfere with the PC, stepper drivers etc. I saw a post somewhere that standard copper wire wound on suitable formers with the ends shorted with a suitable cap will act as an excellent HF/EMF absorbentant. You only need to fix theses formers on or around the machine/apparatus generating the emf. What I would like to know is what is the wire size, how many turns, former material and diameter and cap values. Any help would be appreciated

 

[alec_t]

I don't see how that would be very effective. If the EM interference field is fairly omnidirectional a few absorbers would only be 'hit' by a small part of it and your PC etc would still be subjected to interference.
Can you enclose the HF source in a screening cage?

 

[tcmtech]

I have worked with plasma cutter for years so I know what you are talking about.

The simplest and most effective solution is to use small capacitors on all of the plasma cutters control and lead lines to take the RF to a solid ground at the machine plus do the same to the CNC table motors and leads plus any other control wiring.

After that its just a matter of using a good heavy earth ground lead from each systems primary RF grounding point and frames to a actual earth ground rod or set of them if your local soil is dry.

Also a very effective RF shielding material is a type of aluminum foil tape you can buy at most any home building supply store. It's used for insulation and the like but it makes for a very good metal foil shielding material for exposed electronics and control leads.

 

[Mike odom]

Magic Beads...
just like on the CRT cable coming out of your pc, all control signals entering/leaving an RF field need to have a shield bead in line with them (note that there is a ferrite on BOTH ends of the Display Cable). This is a small coil of wire wound around a ferrite core material. These need to be as close to where the wire enters/leaves the shielding for the PC and/or stepper controller board. I use them on my micro's power supply lines, and hook to the 1/2hp motor power source and can run the micro right next to the motor brushes with out additional shielding.