Re: EMC compliance question

On Wed, 9 Oct 2024 21:29:09 -0400, bitrex <user@example.net> wrote:

On 10/9/2024 7:18 PM, john larkin wrote:

On Wed, 9 Oct 2024 19:03:28 -0400, bitrex <user@example.net> wrote:
 

What's the deal with the "CPU board" exemption?

 
Where is there such an exemption?

>
It's under the section on sub-assemblies:
>
<https://www.ecfr.gov/current/title-47/part-15/subpart-B#p-15.101(e)>
>
A "CPU board" as defined previously is considered a type of sub-assembly.
>
As a hypothetical say someone sells a product that's a PCB with a PIC on
it and some relays that has e.g. RS-232 port and terminal blocks to
connect to other stuff. It's in some sense a functional product, but the
user must at least connect it to some load of their choosing for it to
actually do anything. And they can put it in a housing if they wish, or
not, whatever.
>
Is this still a "sub-assembly"?
>
>

"CPU board. A circuit board that contains a microprocessor, or frequency
determining circuitry for the microprocessor, the primary function of
which is to execute user-provided programming, but not including:
A circuit board that contains only a microprocessor intended to operate
under the primary control or instruction of a microprocessor external to
such a circuit board; or
A circuit board that is a dedicated controller for a storage or
input/output device."
>
So if one sells a board that has say a PIC on it and some support logic,
and the 9kHz+ signals are all internal to the uP (self-clock), but it's
otherwise a functionally complete design other than it's not in a
housing, is that an exempt product?

A sub-assembly is employed inside a listed device - the final device
requiring compliance.

A subassembly is not a stand-alone product and cannot/neednot
demonstrate compliance or even full functionality on its own,
as the housing,interconnection and operational environment is
not present.

If it functions stand-alone, it CAN be tested for compliance, is
self contained and has well-defined IO sources/targets.

Products may contain parts that are self-compliant and list them
as subassemblies, but the final product inherits and is stuck with
that subassembly's red tape.

RL