View Full Version : Harmonics effect on electronic controllers

08-05-2003, 02:21 AM
Does anyone have some experience about the effect of harmonics ( caused by VFD or current rectifiers) in electronic controls like Danfoss EKC 201 , EKC 101 or Eliwell?:confused:

08-05-2003, 03:20 AM
I am worse than rusty on this, but I share your curiosity, aru. What I recall is the effect of inductant loads on the behavior of electronics. Controllers themselves are the victims not the culprits. When you get into variable speed drives, this can be a culprit. In the old days, the culprit was called "noise."

It is why shielded cable is recommended for electronic controller inputs, and why the shield requires a ground... a dump field of sorts in the early language.

There is something about electicity that echoes, whether you call it back EMF or noise or EMI. I use the word "echo" but I meant harmonics.

I understand harmonics on a guitar string and I know the math is predictable, but I fall short of understanding it clearly. I know that frequent on-off switching of loads can also play hell with electronics.

But the largest creator of noise is frequency changing.

I further have a primitive sense that capacitors can filter this noise out when properly employed.

Consider this not so much an answer as it is my support of your question.

750 Valve
08-05-2003, 09:09 AM
Seen the affects many times... wish i had a c.r.o. Have seen CPC einstein screens fuzz completely when v.s.d. ramps up, screen not connected to ground, have used ekc's but not with a Lon card in them so sorry no help. Did notice wiring plays BIG part, all braided wiring on load side of v.s.d. with all wires separated from normal Hz mains supplies, NO data anywhere near, from memory if wires to cross within certain distance then must cross each other perpendicular to reduce "noise" induced into normal supplies and data wiring, some sites analogue signal ground at control end some at vsd end (some if earthed at vsd suffer worse "noise").
Have had some BIG dramas with static build up in CPC networks, had CPC USA gurus out, measured 1900VDC charge???? (dont know where, how or with what???) and proceeded to fit "black boxes" to case control probes, I think its just capacitors to discharge excess static to ground.
An Oz control manufacturer of supermarket controls incorporates a "snubber" circuit on all relays of output cards, this too uses capacitors to limit noise in switching loads.
May be able to dig up some info on wiring specs and recommendations for danfoss VSD's