On Tue, 31 May 2011 11:16:04 +1000, "Phil Allison"
wrote:
The problem with the Extech 380193 Handheld LCR meter is that it will
measure ESR at 120Hz and 1KHz. ESR is usually measured at about
100KHz. Dave Jones mentions this at about 12-13 minutes into his
video. This is because electrolytic cazapitors exhibit a minimum ESR
around 100Khz.
http://www.amccaps.com/leaded-capacitors/switch-mode-ceramic-capacitors/esr-vs-frequency.html
That link shows ESR curves with frequency of a couple of * CERAMIC *
capacitors of unusually high values.
Oops, y'er right. Sorry(tm).
Oddly, while the ESR of the ceramic caps are much lower than
electrolytics, the curve shapes seem to be similar.
Googling, I find:
http://www.low-esr.com/esrfreqperfcurves.asp
Note the dip in ESR and loss tangent at around 100KHz on various
graphs.
ESR meters intended for in circuit testing of electros by service techs
simply measure the cap's IMPEDANCE at around 100kHz. At this frequency -
all but the lowest value electros have their minimum impedances and the
values obtained are very close to ESR values at the same frequency. This
allows one to compare electros for (high frequency) ESR and pick out faulty
examples very easily.
OTOH, the Extech meter is designed to measure L and C values for a wide
range of inductors and capacitors and uses to standard test frequency of
1kHz as used in countless other instruments. This means it is NOT intended
to perform in-circuit testing of L and C value as other circuitry that may
be in parallel may spoil the readings.
However, in the case of electros with values from say 4.7 uF and upwards and
fitted to a TV set I would expect readings to be OK and the ESR values
obtained to be useable. It would be a good idea to re-test any electros
that are removed cos the ESR reading seemed high.
IMO - the 120 Hz frequency should only be used for out of circuit testing.
Yep. Agreed on all points.
..... Phil
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558