On Tue, 19 May 1998, Thomas J Macauley wrote:

> Also, while CAN is a good networking system, there are some environments
> where field busses are NOT a good idea.  I'm still not sure if I like
> the idea of a network controlling the brakes in a car.

The network that controls the brakes is an add-on that serves the ABS and
other refinements. If it fails, then the systems remains a pure
hydraulical brake, as in our grandfather's time ;) Moreover, it is
GUARANTEED to work if electrics fail TOTALLY. Nothing to fear about, the
people who built the car had the same idea, and they were MORE afraid than
you, believe me. From the tiniest engineer and up to the top. And of
course we are talking about cars, and not TRUCKS (which have some
pneumatical paranoia attachements for the case, and pneumatic automation
in the braking section) ;)

> I'm also leery of using PC's as a controller.  Think how often your PC
> crashes, then decide if your factory can deal with that kind of down
> time.  Alos, think about the safety implications.  If a desktop PC
> crashes, it might take out the data on a hard drive at worst.  If an
> industrial control has a problem, it can take off an arm or smash
> someone's head.  (This is also something to consider when brewing your
> own control.)

The PC desktop crashes often because the QC of the OS sux. Moreover, the
firm that mekes it has stated that it does not see an interest in removing
bugs, as this is an investment that brings no returns.

On the other hand, did you get to run something other than the usual OS on
a PC ? Such as, a UNIX flavor (pick your choice: Linux, BSD, SCO...) ? You
should, because out of that point of view (and programming), they are
better than the hardware ;)

Peter