Re: [CAD_CAM_EDM_DRO] EMI Rehab

Hello Abby,

> .Grounding.. foot bones goes the uh.. leg bone, leg bones goes to the..
> uh uh oh! Okay, so the chassis will be grounded, the EMI filter ground
> is common to the chassis ground (well, it's connected actually) but what
> about the parallel port cable? Do I ground the outer shell of that to
> the chassis, or leave it off? Wouldn't grounding this cause the cable to
> be grounded at both ends (PC and controller chasis) and therefore cancel
> out the effect?

Cable shields should be tied to chassis ground at one end only. That
chassis should be tied to ground via the third wire on your power
connector, as it would be with the EMI filtered power entry module that
you are using.

Chassis ground should NOT be the same as signal ground or return,
although it often is. For example, cars and boats usually use the
chassis as signal return.

Various cables sometimes use the shield as signal return or ground.
Avoid cables that do this. An ohmmeter will tell you if the shield is
connected to any pins. If so, those pins should not be used for signals.
The pins might just be connected to the shield for diagnostics.

Tom Hubin
thubin@...