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ludwik kowalski wrote:Ms?
Digital Multi Meters (DMM) sample waveforms and display updated
avarages.
1) Does anybody know what the sampling frequencies are in cheap DM=
the
Long ago Rat Shack sold one that used a dual-slope integrator with
a one-second cycle time. Ewwwww.
2) What are these frequencies in more expensive DMM's?
I have a handheld Fluke (10+ years old) that is good to 100kHz,
true RMS.
I have (relatively) cheap National Instruments boards lying around =
lab that are good to 20MHz.eird
4) Any potential traps in using DMMs?
More than I know how to count.
Perhaps the biggest one is Dragon Breath: The instrument injects w=
noise out of its input into the device under test.y,
There are many types of Dragon Breath. One kind arises if the
nominally-floating (i.e. gauge invariant) probes aren't quite,
i.e. there is some nontrivial impedance (usually capacitive) to
the rack and/or the "ground" of the power line.
Then there's aliasing at high frequencies.
Then there's eyeball-aliasing, if you only look at it intermittentl=
as opposed to logging *all* of the data._______________________________________________
Sensitivity.
Linearity.
Multiplicative calibration errors.
Additive DC offsets.
Non-infinite input impedance.
Thermocouple effects, if the thing you're measuring isn't at room
temperature.
etc. etc. etc.