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Best CHEAP LCR meter for small capacitors and inductors?

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pqass:
I know you're probably not looking for a DIY LC meter now, but in case you've hit a wall, consider the LC-meter project below (or at least the oscillator part).

I'm currently implementing the LC+LM311 oscillator [on perf-board] just to validate the approach before committing further. See attachment.  I'm using a bread-boarded [reciprocal] frequency counter (which I happen to have handy) but any bench counter will do.  Also, I've removed the need for relays in my version; replaced with a DPDT and BJT.

See Part 1 of the video at
  10:28 for the theory of operation.  (https://youtu.be/KhJiE4gL5T4?t=628)
  16:26 for the six formulas involved  (just one frame at https://youtu.be/KhJiE4gL5T4?t=986)
  17:54 for the algorithm on how to determine C-DUT or L-DUT  (https://youtu.be/KhJiE4gL5T4?t=1074)
        To summarize:
        (a) first measure the freq. without any C-DUT attached,
        (b) then turn on calibration cap BJT (still no C-DUT),
        (c) then, attach a C-DUT (w/o cal cap) and measure freq.; use formula 5 to determine value.
            OR attach L-DUT (w/o cal cap) and measure freq.; use formula 6 to determine value.
        Calibration steps (a) and (b) only needed every once in a while.

I've successfully measured down to 16pf (all I had) just using manual recording of the frequencies with/without DUT and calibration cap into a spreadsheet.  Measuring inductors yields values close to whats printed, although, in the 10s of uH to 100mH; I don't have any nH inductors.  The chosen L+C values has problems with >1uF C-DUTs so I'll be exploring other combinations to determine ranges. 

FYI: I'm just a hobbyist (no EE) and as such, am not (yet) knowledgeable on the intricacies of those fancy HP LCR meters on eBay. But this appears to fit my C and L measurement needs and may be worthwhile for you. Also, in case you're wondering, the reciprocal frequency counter on the b-b [74HC4020+74HC74+ATTINY84] is based on www.instructables.com/High-Resolution-Frequency-Counter/ (good to 7 digits) but I've done a major rewrite of the software.


Original LC meter project links:
Hackaday IO: https://hackaday.io/project/178081-build-an-lc-meter
Github: https://github.com/coreWeaver/LC-Meter
Look for parts 1 thru 5: https://www.youtube.com/channel/UCSwxZFW1XBvgM92nI7XMwSA/videos 

Measuring Femto Farads:

ranchero:
I would love to participate in this project, but unfortunately I'm not in the position when I can spend time on it. 

mawyatt:
Generally small inductance is more difficult to measure than small capacitance. One fundamental reason is inductance is highly dependent on length, whereas capacitance is inversely so, and at a moderate frequency a small capacitance has a relative high impedance whereas a small inductor is low impedance.

As you move up in frequency the capacitive reactance drops and the inductance reactance increases, however for small L like 100nH is only ~ 0.063 ohms at 100KHz and a small capacitance of 100pF is ~ 15.9K ohms. So getting a good "zero" reference for the L is difficult, but relatively easy for C.

As mentioned by 2N3055 a VNA is maybe a better choice is some cases, and for small inductances this is the case!! The usual VNA is a low 50 ohm instrument that allows moving the "reference plane" up to the DUT fixture, thus removing the setup and fixture "length", LCR meters don't do this, although some of the lab types do have a "cable length" option which compensates for the test cable phase shift.

Measuring small capacitance ~100pF can be achieved with even a DMM capacitive measurement in a pinch, one must carefully null out the residual and keep the cables fixed in place (tapped to the workbench for example). Heck, Dave even showed how to measure Inductance with a DMM in his April 1 Video  ;D

Best,

thm_w:

--- Quote from: ranchero on November 23, 2022, 02:15:41 am ---
--- Quote from: thm_w on November 23, 2022, 01:47:06 am ---Just because its not entirely clear what OP is doing.
If its in circuit measurement then the tweezers are great to have. If its measuring a part, very precisely, prior to install, then maybe the mentioned SMD jig with a DE-5000 would be more repeatable.

--- End quote ---

I don't think it's even possible to measure such small values correctly in-circuit. So - I always remove them. The tweezers you've recommended only go up to 10kHz, so they will not measure small inductors.

--- End quote ---

It just depends on the circuit in question, there is no blanket answer. If you know a specific inductor has nothing in parallel with it, then it will measure OK.

Those tweezers can measure a 0R 0603 at ~5nH in circuit. BUT thats very much in the noise, and I would not consider it repeatable at all. Which is where a jig is better (consistent distance, pressure, etc.).

Vojtech:
As Mawyatt mentioned, measurement of nH at 100 kHz needs mOhm resolution, so 4 wires Kelvin is a must. A quick test of ET432 with shorted inputs at 100 kHz - resolution is down to pH, the result is stable to some hundreds of pH. Capacitance measurement at 100 kHz with open input – offset is some tenths of pF (can be nulled out), the resolution is 1 fF, the result is stable to 1 fF. Of course, the moving of cables changes measured capacitance with some tenths of pF. I have no etalon of low caps or inductors, so I am not able to verify absolute accuracy. Still, its meaning is questionable – with such low values parasitics in real PCBs play a significant role so absolute accuracy is questionable here. I think ET432 is better than DE-5000 with still an acceptable price.

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