[Test-Equipment] Fw: Probe Refresher

[David]

On Fri, 12 May 2017 13:05:59 -0400, you wrote:

>    Doug Hensley wrote in part:
>
>   /* snip */
>> Lastly, if a scope can tolerate 400V at its input (as in case of 2465B), hooking up a 10:1 divider probe does not mean that now you can push 4000V before causing damage. This is because most divider probes are also only rated for 400V or so.
>
>   For higher Voltages 100 and 1,000 to 1 probes are available, at the 
>higher Voltages the probes are pressurized with a special gas to keep 
>the probe from becoming a monstrosity.

There is another thing to beware of with attenuating probes and
especially most x100 probes; most x100 probes do not attenuate the DC
signal before the oscilloscope input!

Most cheap x100 probes have voltage ratings from 1.2 to 2 kilovolts
but are composed of just a 99M series resistor (plus compensation
components).  So if the oscilloscope is set to use AC coupling, the AC
coupling capacitor will charge to the DC value at the probe tip easily
violating the oscilloscope's maximum input voltage causing breakdown.
Do not use these probes at high voltages with AC coupling selected!

Better, or at least safer, x100 probes have a lower valued input
resistor and a shunt resistance so they divide the entire signal
before it reaches the oscilloscope input and are safe to use with AC
coupling.  These can be identified by their specified input resistance
which will be lower than 100 megohms.

x1000 probes always have the shunt resistance.