There seems to be many misconceptions/misunderstandings about Capacitor ESR, this is just a parameter that helps describe the capacitors loss in a simple 2 element capacitor series model, C + ESR, or 3 element series model C + ESR + ESL. ESR simply lumps all the capacitor losses into one simple parameter, similar to Capacitor "Q" which represents overall "Quality" which shows relative Reactance/Rloss, or 1/(omega*C*ESR).
Unfortunately ESR is a highly dependent variable with frequency, waveform type, capacitor type, value, applied voltage, temperature, age, history and so on, which often prevents one from precise results, and makes it difficult to pin-down a specific reading with any confidence. Some capacitor types have a more repeatable ESR measurement, such as some large value PP Film types.
ESR tends to be low values which place importance on cables/fixture, setup and calibration (Zero/Short specifically), which adds additional uncertainty in measurement.
However, ESR measurement is not all Black Magic, as one can achieve respectable results with good engineering practice. First off, one needs to KTI (Know Thy Instrument) and how the results displayed are created. Significant differences exist in operation between the low-cost All-In-One Testers and LCR Meters, even between LCR dedicated instruments themselves!!
One also needs to understand the DUT under investigation. For example, ESR is highly temperature dependent in most large value Electrolytic/Polymer Capacitors. During measurement Lab Grade LCR Meters can produce significant DUT current, often greater than 100ma RMS!! This current heats the capacitor internally by means of I^2 *ESR which changes not only the Capacitance but also the ESR readings. One can experience this effect by simply watching the Capacitance and ESR readings change as time moves on, and should wait for these to stabilize for a more repeatable result.
Since low Z values are present where ESR is usually of concern, setup and fixtures play an import part in achieving repeatable results. One should study the various resources (some on here) for these and become intimately familiar with if repeatable results are expected.
Calibration is extremely important for quality repeatable measurements of any kind, especially true for Short/Zero Calibration for Low Z, ESR is no different. Lab Bench LCR meters often have an extensive Calibration Routines which should be employed, and some fixtures require specialized means for Calibration. For example the popular Leaded Component Fixture such as the Tonghui TH26048A has a specialized Zero Metallic Blade TH26010 for quality Zero Calibrations.
Anyway, the general message here is that repeatable ESR measurements are indeed difficult, especially so between different instruments, but with patience and good engineering practice can be reeled in to respectable results.
Here's a quick example achieved with various capacitors and LCR Meters TH2830, IM3536 @ 1KHz and Multi-Function Tester T7. Results shown C in uF and (ESR in ohms).
As always YMMV
TH2830 IM3536 T7
43.7068 (
0.4911) 43.7060 (0.49879) 44.78 (0.52)
945.931 (0.03833) 946.561 (0.03788) 1028 (0.11)
424.159 (0.06465) 424.435 (0.07221) 440.2 (0.15)
95.6551 (0.04040) 95.5962 (0.04214) 96.84 (0.11) Polymer
9.85790 (0.06412) 9.85680 (0.06405) 9.377 (0.08) Polypropylene
4.90324* (0.00338) 4.90205 (0.00813) 4.651 (0.07) Polypropylene
*Edit, added. Even with careful Setup and Calibrations, Leaded Capacitors with very low ESR (<10 mill-ohms) present a difficult measurement. Here a special fixture which reduces lead and contact effects would be appropriate, similar to what was developed for very Low Z SMD Components.
CorrectedBest,
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