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Twisted pair, effect on non balanced/differential systems?
MFX:
I know the principle behind using twisted pair cable for differential (RS485, Ethernet, USB etc. etc.) and balanced (Microphones etc.) systems but occasionally I see people suggest that using twisted pair can reduce noise pickup problems on non-balanced systems, E.G. a microswitch connected to a microcontroller with just a 5v and Gnd wire between them. Does using twisted pair have any noise pickup reduction benefit in this case and if so how much (roughly) benefit compared to a proper differential system?
Cheers.
Martin.
pwlps:
I found this picture in my archives unfortunately I can't find the book reference. As far as I understand floating loads mean differential (balanced) input, but A,B,C represent single-ended inputs. For these there is apparently no much difference between a coax and a twisted pair. I find it a bit strange because I thought a twisted pair should reduce the magnetic flux much better than a coaxial cable. I'm curious to understand it too.
David Hess:
With a common mode connection only on one end, twisted pair or coax reject magnetic interference very well. As shown above however if both ends are connected, rejection is very low. In that case other steps are necessary like common mode filtering, transformer isolation, or an instrumentation amplifier.
The pair of wires could also just be bundled together; magnetic flux caught between them is what causes problems. The idea is to minimize the "loop area".
Marco:
--- Quote from: MFX on June 11, 2020, 03:58:54 pm ---non-balanced systems, E.G. a microswitch connected to a microcontroller with just a 5v and Gnd wire between them.
--- End quote ---
How is that non balanced? The currents are exactly balanced.
MFX:
--- Quote from: Marco on June 12, 2020, 03:22:01 pm ---
--- Quote from: MFX on June 11, 2020, 03:58:54 pm ---non-balanced systems, E.G. a microswitch connected to a microcontroller with just a 5v and Gnd wire between them.
--- End quote ---
How is that non balanced? The currents are exactly balanced.
--- End quote ---
"Balanced" is the term used in audio world for what is basically a differential system. Rather than signal and ground you have signal and inverted signal.
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