Anyone who has done this work more than a few years knows the liturgy;
it starts with cost, moves to expense and ends with failure.
I might be one of the EMC engineers you describe, because truly,
following very simple design principles costs little, done at the
outset, and averts much. But that is often overlooked.
Why did a board layout route ALL the data and address lines all the way
around a processor? The factory wanted all pin 1's in the same direction
to better control wave soldering, or so they said.
Why was a hard-drive cable run RIGHT across a chassis opening for its
not-installed mate? Because it would disrupt production to rearrange
wires on spools at each assembler's workspace.
Why did I have to argue two hours with a mechanical engineering VP to
get parts of a chassis to touch? Because an interference fit is
mechanical blasphemy, tooling for the progressive die would have to be
modified, and someone was sold on a "labyrinth" stopping EMI from
getting out.
Why did another company spend near half a million dollars testing and
retesting equipment at an outside house when it already had enough
equipment for pre-tests? Because there was no budget for the engineers
who should have done it.
I could go on, but I don't need to. Not here. We all know some sorry
story of cost cutters who ruin budgets by overruling engineers. And you
can't fool physics.
Aunt Enna: "Johnny! You put that electron back before it screams for its
mother!"
That'll do, for a start.
Cortland Richmond
On 3/29/2012 2323, Richard Nute wrote:
I once worked with an EMC engineer who measured
the performance of himself and his time by the
cost of the components that were used in the
equipment solely for the purpose of EMC control.
His objective was to reduce the cost of compliance
by advising designers of careful layout so as to
minimize the need for EMC components.
Safety is a bit different because many safety
components are also functional components.
Nevertheless, a ground wire can be eliminated if
double-insulation is employed. In this example,
a cost trade-off between the power cord and the
extra insulation. But, these days, most primary
circuit designs are indeed double-insulated as
transformers simply don't use internal shields.
Enclosures... only needed for primary circuits
and secondary circuits exceeding 30 V. (Yes,
you still want an enclosure, but not for safety!)
Etc. So, compliance should not cost too much.
I look forward to your comments on compliance
costing too much.
Rich
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