On Fri, 16 May 2003 20:33:06 +1000, "Bushy" <please@no-spam>
wrote:
>G'day Dee,
>the cross is cool, it could be answered by one of the groups and I only look
>at a.e.
>
>I've used printed circuit board to provide a shield for some sensitive
>industrial gear, where the price wasn't so important, and being able to fit
>it together in the space was. If you are on a budget, it could be made out
>of almost any piece of scrap metal sheet with a wire to earth and a second
>layer of some insulator like a cut up old tyre tube or icecream container.
>
While the icecream container is a great idea for cheap insulation
material - I would be careful in some applications using this or other
such "consumer single use" plastics. I have done so before and have
found that some of the modern ones they split / fall apart over time.
( This probably would accelerate in hot conditions too ?). I think the
problem is that the modern plastics are meant to degrade for
environmental reasons after disposal.
>
One great alternative for such things is the use of scrap perspex
pieces. usually can get offcuts from sign places etc. I also collect
aluminium offcuts too - they are often available free or cheap from
sheet metalworkers.
>
>You may need to cover the offending circuit with an earthed box structure or
>maybe simply an earthed plate between two boards that interfere with each
>other. Simpler is often all that is required, but make sure you have it
>mounted sucure enough to hold it in place when the computer is moved. You
>don't want it falling over and shorting out things.
>
>Side on view could look like:
>
>Circuit board one
>Insulating layer
>Shield connected to ground
>Insulating layer
>Circuit board two
>
>The insulating layer might be air and the mounting screws or brackets
>providing enough support to prevent shorts. If you have a friend look over
>your design before you power it up you might find the second pair of eyes
>spot a problem before it creates lots of smoke and sparks.
>
>Have a look in a number of TV's and see the little boxes they use to cover
>some bits they use to shield things. Used to be more common in older designs
>and the old valve jobs often had shields over each tube and a number of
>other bits.
>
>On some equipment you have to provide new fans to keep things cool as the
>shield might prevent normal airflow while on others the extra metal provides
>more heat transfer and nothing is needed.
>
>Hope this helps,
>Peter
>