Re: [CAD_CAM_EDM_DRO] Re: Re: Ground loop boogieman ... can someone explain this

Alan,
It is indeed the AC component that is the big cause for concern in 'ground
loops'. Remember what a transformer is - 'loops' of wire. The problem is
magnetic fluctuations in the proximity of a ground loop will induce currents
(and therefore voltages) withing the loop. In your example:

>
>If you were to add another wire like so
>
> |----------r5--|
> 0v ---r1--A---r2--B
> * *
>+5v ---r3--C---r4--D
>

the loop can act as a transformer and all sorts of nasty voltages can occur
in the presence of magntic flux (coming from transformers, wires carrying
switching currents etc). It would actually be possible for B-D to
instantaneously see *more* voltage than A-C.

The concern with us is often times these induced voltages can cause inputs
to exceed the somewhat low 0.7v TTL input logic 1, or worse yet go below
ground.

Yes, multiple return paths can improve the DC characteristics of a circuit,
but if they're interconnected they will act as an antenna.


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