Oz, in DFW
lists at ozindfw.net
Sat Aug 14 19:14:14 UTC 2010
On 8/14/2010 10:08 AM, J. Forster wrote:
> FWIW, IMO any engineer who uses undocumented or uncontrolled parameters or
> instructions in a production design is a fool.
> If you are that silly, you must fully specify the selection criteria.
This is, easily said, a wonderful goal, and absolute fantasy. It's
optimistic at best to expect someone to anticipate all contingencies.
It's certainly good practice to specific critical parameters, but it's
rarely makes economic sense to specify every possible detail.
As to relying upon unspecified parameters, most datasheets are woefully
incomplete. If you are going to use any significant number parts, it's
unlikely that you'll be able to get everything specified, much less get
compliance commitments for each parameter. Few vendors are willing to
do the testing required to guarantee a substantial number of parameters,
and the simple reason is no one is willing to pay for it.
I've spent quite a bit of time dealing with maintenance of military
systems that would be long obsolete in any other business. After
obsolescence, the number one problem was parts that meet all published
specs, but had changed performance so much (for better or worse) that
they no longer functioned in the application. A common problem is Ft or
gain, but leakages are often orders of magnitude different. As often as
not, they were much worse.
mailto:oz at ozindfw.net
Southlake, TX 76092 (Near DFW Airport)
More information about the time-nuts