Other than investing in an expensive tweezer type meter for SMD components, what would be a good method for the layman to find the capacitance of an 0805 ceramic capacitor whose value is below 1nF? My Fluke meter can only measure to 1nF...
5
-
\$\begingroup\$ If you insist on accuracy, buy a Agilent U1733C LCR meter. It is not cheap, but it will take the guess work out of de-bugging problems. It cost about $450 USD to $500 USD, depending on vendor and any 'bargains' they may have. Example: My Fluke 87-5 goes for $420 USD, but I found it on sale with a temperature probe for $386 USD. Only the best LCR meters can read down to tens of pf, or have 10pf resolution. \$\endgroup\$– user105652Commented Oct 24, 2018 at 0:55
-
\$\begingroup\$ If all you have is a Fluke (no oscilloscope, etc.) then the only other semi-practical DIY technique would be to solder (unfortunately) the capacitor into an op-amp based astable multivibrator. That would create an oscillation frequency inversely proportional to the the capacitor value (I would test the circuit out with some known value test capacitors to make sure it works, and that the formula calculations are correct as well as correct for stray capacitance at the 100pF and below range. Otherwise you're stuck with buying tweezers. With a scope you could do a direct RC time constant check. \$\endgroup\$– user201365Commented Oct 24, 2018 at 3:15
-
\$\begingroup\$ You should use an op-amp buffer to the scope probe to reduce loading effects that would affect accuracy. Practically speaking you have a 1:1000 range in values, and once it gets down into the picofarad range you really want to calibrate the circuit by substituting known values. This assumes your Fluke has a decent frequency counter range. You can cross-check by putting in a known value and comparing the frequencies. \$\endgroup\$– user201365Commented Oct 24, 2018 at 3:16
-
\$\begingroup\$ Put in a square wave, perhaps the scope's probe-calibration signal. Create a low-pass-filter with 10uS timeconstant, likely a lot slower than the cal-waveform. For 100pF, use 100Kohm. Remember the scope-probe has 13-15pF. \$\endgroup\$– analogsystemsrfCommented Oct 24, 2018 at 4:09
-
\$\begingroup\$ @analogsystemsrf Siemens isn’t a unit of time, mate, nor is Kelvin a prefix. \$\endgroup\$– winnyCommented Oct 29, 2018 at 6:57
Add a comment
|
2 Answers
\$\begingroup\$
\$\endgroup\$
You could buy one of those cheap Chinese LCR meters. About $6-10 including shipping and they'll measure down to 30pF or so.
Here's a 47pF 50V 0805 capacitor measured with hand-held jumper leads:
I would check it with my LCR bridge if it was important but you can't beat the price/performance of these things. The design has evolved from a US published front end and hobbyist copy using an AVR and the published equations.
--sp
answered Oct 28, 2018 at 22:45
\$\begingroup\$
\$\endgroup\$
The quick and cheap and easy solution. This Bside ESR02 Pro seems to have gotten me the correct capacitance and the replacement parts are accurate! This read 320pF off a 0805 capacitor! Success!