[Elecraft] Multimeter Altitude Limits

[Ron D'Eau Claire]

What's the upper voltage limit the DMM will handle? 

Resistors have a voltage rating as well as resistance and wattage
(dissipation) ratings. We don't normally run into the voltage rating with
leaded parts, especially with low-voltage solid state gear, but it's a very
real concern as the voltage gets "up there". That's why high voltage probes
have big, long resistors or a number of resistors in series -
shorter/smaller ones would arc over.

In a DMM, the voltage divider that determines the voltage range is usually
made in one piece, using tiny resistive elements on a substrate. Compared to
"normal" resistors, each resistive element is tiny, and the voltage required
to produce an arc drops dramatically as you go up in altitude. 

Radio equipment intended for use in an unpressurized aircraft or an
unpressurized area in an aircraft is usually pressurized to avoid that
corona discharges and arcing (as any tech will tell you who forgets to
depressurize an aircraft radio before removing the cover bolts to service
it. Me? Naw..... The cover missed me by half an inch, at least...). 

If your DMM will measure a few hundred volts, I'd surmise arcing in the
voltage divider is the limiting factor for altitude.

Ron AC7AC