Q: Building a small machine room? Materials/costs/etc.
James.P.Lux at jpl.nasa.gov
Thu Sep 18 19:58:21 EDT 2003
At 12:25 PM 9/18/2003 -0400, Robert G. Brown wrote:
>On Thu, 18 Sep 2003, Jim Lux wrote:
> > So, what you probably want is a sort of staged setup.. moderate overtemp
> > shuts down computer power, bigger overtemp (i.e. a fire) shuts down the
> > blowers, pressing the big red button next to the door shuts down all
> the power.
>We have some of these (including the big red switch by the door) but not
>all. Maybe soon -- the first is really a matter of sensors and scripts.
Personally, I prefer not relying on a computer (that's doing anything else)
to shut down the computer for a serious overtemp. I'd rather see a sensor
and a hardwired connection to some sort of relay. OK, I might go for a
dedicated PLC (programmable logic controller), but I'd want it to be rock
solid and robust in a variety of environments, something that no PC is ever
going to be (PCs are just too complex with too many logic gates
internally). Sometimes simple is good.
The sensors and scripts would be good for the graceful shutdown as you get
close to the "yellow limit".
Anyone who is enamored of the total software control of things that can
cause physical damage should remember one word: "THERAC-25"...
Nancy Leveson at MIT has a site at http://sunnyday.mit.edu/ where there is
much about software safety.
James Lux, P.E.
Spacecraft Telecommunications Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
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