ESR meter - DIY - what do you think of this one?

[lee321987]

Hello. I want to build this simple ESR meter.
I was wondering what you guys think of it.

https://electronics-diy.com/electronic_schematic.php?id=948


I especially wonder about it running at only 2.3kHz.
Aren't we supposed to test capacitor ESR at around 100kHz?
Would it be okay/necessary to alter the 555 circuit to run around 100kHz?

Also, there is a "47uF NP" capacitor near the lower-right -- does that mean "non-polarized"?

 

[Kripton2035]

you can get a lot of info here:
**broken link removed**
and a lot of other free schematics better than this one ...

 

[lee321987]

Thank you.
One of the projects on that page is just the schematic, and the source is apparently gone, but wonderfully the web archive has it saved!
https://web.archive.org/web/20101023201524/http://octopus.freeyellow.com/99.html

I ended up building it, and it works great.
He uses a 555 timer as a function generator, with an oscilloscope to measure. (also boasts of "quite usable" results with a simple multimeter)

I just have one question. Mr. Powell says on the original page:

[...] the ESR can be found by either comparing the test results with those from resistors of similar value, or by calculating using the formula for parallel resistors.

It works by testing the voltage drop across a known (10 ohm) resistor, then you connect the DUT in parallel with the resistor, and note the difference in the voltage drop.
Here is where some equation comes in, but what is it?

He has a chart at the end that you can conveniently use, but i would like to know the equation. Please, if anyone can help.

Schematic attached: