:: ESR frontend? ::

[3roomlab]

Hello EEV folks, just happen i was tickled by looking at a number of ESR projects going around (and googling a screen full of schematics), i threw a couple of pixels into the multisim to have some "LEGO" time, and i came to this particular juncture.

from this cropped diagram, is it safe to say i have a practical ESR frontend to "probe" stuff? the known current drive (1ma) gives a direct read off in "ohms" via the potential difference (XMM2), is that all to it or there is something i missed?

the "signal" is injected from the top right "leg" (grounding return is on the left), 1kHz pseudo sine 200mv p-p. there seems to be some simulated internal resistance somewhere and R20 was "adjusted" so that a shorted test probe (replaced with a switch S1) will yield 1mA (or 997uA p-p seen on probe4)

for C5 and C6, i found some low ESR 22u caps on element14, they rate at 0.015ohms. so in actual, i am assuming that the real C5/6 will not give a readout of 5.4ohms, am i right? (i did a re-run with C5/6 removed and it does seems to be so, see lower half of pic in black and white).

any comments? (i keep wondering if i missed some theory somewhere as it seemed just too easy to just read off ohms from the mV scale)

[jimmc]

You are using too low a frequency, the reactance of the capacitor is not negligible.
See here for an explanation http://midwestdevices.com/_pdfs/Tnote3.pdf.
Once the frequency is high enough, sine or square makes little difference although the harmonic content of the square wave can cause problems with the inductance of leads etc.

Jim