On Jan 24, 5:55*pm, David Nebenzahl wrote:
On 1/24/2011 5:20 PM Jeffrey Angus spake thus:





On 1/24/2011 6:40 PM, William Sommerwerck wrote:

Set the audio gen to about 100kHz and connect the output across
the electro under test -- then connect the scope probes directly
to the same cap (not the generator). You should see a small
voltage at 100kHz on the scope.

If one takes that literally, the scope probes /will/ be connected
directly to the generator.

Did you leave something out?

Nope, it IS connected directly to the generator.
And the capacitor across both.

You see a reduced value of signal due to the ESR of the capacitor
vs the source impedance of the signal generator.

Pretty simple.

Not direct reading, but accurate comparison.

Skimming through a bunch of ESR meter schematics, this seems to be the
game plan for most of them:

* *Oscillator -- attenuator -- cap under test --
* *op amp/comparator -- rectifier -- meter

(osc. is usually around 50-100 kHz)

Gots to build me one someday ...

(the attenuator delivers only millivolts to the cap being tested,
avoiding electrolytic polarity issues and any semiconductor junction
resistances)

--
Comment on quaint Usenet customs, from Usenet:

* *To me, the *plonk...* reminds me of the old man at the public hearing
* *who stands to make his point, then removes his hearing aid as a sign
* *that he is not going to hear any rebuttals.

Not likely to do much better than the MUL3333 ESR meter from Mat
Electronics for $50. The main 'quirk' on the unit is the battery case
holds 6 AA cells but it's wired as 3 parallel groups of 2 cells
meaning just use 2 AA cells and skip the other 4. Very good value for
the money. With any ESR meter there are 'gotchas' to beware of. Any
ceramic caps in parallel with a 'lytic will mask the true condition of
the 'lytic. If it reads bad, it IS but if it reads good it might not
be. May times I've run into boards with many caps of the same value.
If one of those is bad I change all of that value figuring if one is
bad the others aren't far behind. Also, the output caps in SMPS need
to be nearly perfect. 'Good enough' rarely is. When in doubt toss em
out.

http://www.matelectronics.com/

G²