| Electronics > Beginners |
| LCR meter ESR measurement seems off - What am I doing wrong? |
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| jackbob:
When measuring capacitors to determine if they meet spec, particularly with electrolytics, the test frequency is very important and can yield very different measurements. Most electrolytics are tested and rated for 120Hz and that meter is surely capable of testing at that frequency. The reason for this test frequency is because most electrolytics will see the output of a full wave bridge which has a frequency of 120Hz as a result of the full wave rectification of 60Hz AC. This will yield much different results than a capacitor tested at 100KHz. The 100KHz is not typically used for electrolytics except to measure ESR and high frequency characteristics for capacitors rated for high frequency switching power supply applications. This video is a very good resource for information related to this topic. I hope there isn't any issues posting a video like this. Someone please let me know if this is a no no. |
| jdurango:
Thanks! Yeah the one downside of the U1733c is that it doesn't have an option for 4 wire leads, so I couldn't really get the full benefit of Kelvin clips. Although if I could get longer leads somehow, and still get it to calibrate with decent measurements, that would be nice! |
| ogden:
--- Quote from: jdurango on March 29, 2019, 08:02:35 am ---So it sounds like the LCR is more likely to be accurate with elytics and I should judge whether or not the cap is within spec using that reading, and not so much the DMM? --- End quote --- Indeed - trust your LCR instrument. Capacitor function of multimeters usually is not primary mode but "nice to have" one. Your LCR is 0.2% while DMM is 1% (for 0.2 - 20uF ranges). LCR measures *real* capacitance, ESR and dissipation factor and more, while DMM measures (using charge/discharge) just capacitance and you can only guess - measurement is degraded by poor ESR and dissipation factor or not. Yes - DMM may be way off promised 1% for capacitor with poor ESR&DF. When there's parasitic inductance involved, results of DMM cap measurement may be even unpredictable. --- Quote from: jdurango on March 29, 2019, 08:53:44 am ---Yeah the one downside of the U1733c is that it doesn't have an option for 4 wire leads, so I couldn't really get the full benefit of Kelvin clips. --- End quote --- Don't bother. You would benefit from Kelvin clips only for last few "small ranges" of R, L, C (2 Ohm, 20 uH, 20 pF). |
| jdurango:
Thanks! Very helpful! Can I at least get slightly longer test leads? Are there any you can recommend? I know it might make readings a bit more jumpy, but as long as it will still self-calibrate and yield decent ESR readings I'd love to at least have the option if needed. There are instances where it would very much come in handy. Thanks! |
| ogden:
--- Quote from: jdurango on March 29, 2019, 09:16:13 am ---Thanks! Very helpful! Can I at least get slightly longer test leads? --- End quote --- No. Strictly not recommended. When you know everything about LCR impedance measurement and would understand what is influence of long test leads for particular measurement at particular frequency - use any test leads you want. LCR measurements are not that simple as it may look: https://literature.cdn.keysight.com/litweb/pdf/5950-3000.pdf [edit] Longer test lead "upgrade" would be valid for kelvin 4-wire compatible LCR meter. [edit2] There is kind of longer leads, in form of SMD tweezers: https://www.keysight.com/en/pd-2143789-pn-U1782B/smd-tweezer?cc=US&lc=eng. |
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