electro-Physics: 17.3409 volts

From: Eric Smith <eric_at_brouhaha.com>
Date: Mon Dec 13 17:30:01 2004

Tim wrote:
> For not-so-heavy transformers, higher frequencies are desirable, thus
> the 400 Hz AC power on military aircraft.

And civilian aircraft as well. When I flew from San Francisco to London
in 2002, I had to make arrangements to use my CPAP machine. They were
concerned because the machine is rated for 50 to 60 Hz. But it uses
a switching power supply which is actually perfectly happy to run on
400 Hz, so I was able to use it. It's irritating that the manufacturer
defines the rating based on what power they expect the user to have,
rather than practical operational limits.

Unfortuately, the mechanic assigned to wire the outlet for me (by a
long extension cord and an adapter from the aviation power plug to
a standard NEMA 5-15R receptacle) apparently plugged it into the
"ground service bus" which is intended for non-flight use for vacuum
cleaners and such, and is automatically turned off on takeoff. So
I had to stay awake for the whole flight. On the return I asked them
to make sure it was NOT wired to the ground service bus, and it worked
fine.

Speaking of annoying specifications, I was just reading the manual for
an HP logic analyzer circa the mid-1990s. They make a distinction
between "specifications" and "characteristics", defining the former
to be something they actually test the instrument against, and the
latter to be non-tested and non-guaranteed. They list the maximum
clock fequency and minimum clock pulse width as specifications. But
they list the number of channels and the memory depth as
"characteristics", which means that if the analyzer only had 67
channels instead of the "characteristic" 68, they could still claim
that it met the specifications. In practice I'm sure they wouldn't
try to screw customers on that point, and couldn't get away with it
anyhow because the channel count and memory depth are prominently
featured in the sales literature. But after they go to all the
trouble of explaining a distinction between specifications and
characteristics, it seems really bizarre that they would put the
channel count in the latter category since it is clear that they
do actually have to test them all.

Eric
Received on Mon Dec 13 2004 - 17:30:01 GMT