Twisted wires are good & free
Posted by
Geoff Bullough
on 2000-08-07 05:53:29 UTC
Hi,
There was a question about shielding wires. I think you can avoid a lot of mysterious problems if you can stop interference from high power circuits getting into signal circuitry coming from your PC. For those of us without a lot of theory and fancy equipment here's some basic help:
Using an earthed screen is not the same as twisted pairs. A twisted pair is not just one wire wrapped round the other, but both of them twisted together. The more twists per foot the better it should work. If you can arrange for outgoing high-power to be twisted with its return (normally you may think of this as earth/ground) then the current flowing round the twisted wires will be in opposite directions and this should cut down the amount of energy radiated. For signal wires the interference should be in opposite directions and balance out.
Of course, in the real world nothing's ever that good, but it's free and it could help a lot. It's still a good idea to have an earthed screen (grounded shield); that keeps other interference out.
If anyone wants to think about it more deeply ,some transformers have a ground shield between primary and secondary, but that doesn't stop the current being induced in the secondary, which in that case is what you want.
Regards,
Geoff
[Non-text portions of this message have been removed]
There was a question about shielding wires. I think you can avoid a lot of mysterious problems if you can stop interference from high power circuits getting into signal circuitry coming from your PC. For those of us without a lot of theory and fancy equipment here's some basic help:
Using an earthed screen is not the same as twisted pairs. A twisted pair is not just one wire wrapped round the other, but both of them twisted together. The more twists per foot the better it should work. If you can arrange for outgoing high-power to be twisted with its return (normally you may think of this as earth/ground) then the current flowing round the twisted wires will be in opposite directions and this should cut down the amount of energy radiated. For signal wires the interference should be in opposite directions and balance out.
Of course, in the real world nothing's ever that good, but it's free and it could help a lot. It's still a good idea to have an earthed screen (grounded shield); that keeps other interference out.
If anyone wants to think about it more deeply ,some transformers have a ground shield between primary and secondary, but that doesn't stop the current being induced in the secondary, which in that case is what you want.
Regards,
Geoff
[Non-text portions of this message have been removed]