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LCR vs ESR meter for in-circuit testing of electrolytic cap
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RiRaRi:
Thank you. That is good answer. I was thinking about getting DER DE5000 but as i can see it acctualy has a lot of problems and not consisted readings. Is there alternative?
I think it would be the best to have ESR70 for in-circuit and proper LCR for out of circuit. Is there some better alternative to der dee but not as expensive as BK880?
Veteran68:
You keep implying the DE-5000 is unreliable. It is not. For what it is, you will really find no better instrument in its price range. There are comparable products in the same formfactor (Hantek 1830/Uni-T 622/EastTester 430 series) that provide a better UX and a few more parameters like additional test voltages & frequencies, but functionally they are all comparable to the DE-5000.

As others keep pointing out, NOTHING will give you total accuracy for in-circuit measurements. You need to calibrate your expectations a bit. Exact accuracy should not be your goal, as measuring ESR is not an exact science, especially in-circuit. It's not like a voltmeter which if in spec will produce virtually the same result as any other in-spec voltmeter. Just look at the example measurements Kean posted above from a variety of instruments. You'll virtually never get the same result from different devices.

The DE-5000 is more capable in terms of features and usefulness than the ESR70. Both have a purpose and are great if you can afford both, but if you can only buy one, the DE-5000 will serve you better overall.
TimFox:
 "I was thinking about getting DER DE5000 but as i can see it acctualy has a lot of problems and not consisted readings."
Why do you keep saying it has a lot of problems and inconsistent readings? 
Have you used one?
I saw one whining complaint because it did not remember the previous setting when power was cycled--no big deal, since you need to "calibrate" the unit each time for accurate measurements (calibration here means compensate for the external test fixture or leads).
I have one and think it is an excellent value for its low cost.
Before retirement, I used an excellent bench LCR meter (QuadTech/IET 1730T) which is far more flexible, much larger and heavier, and much more expensive.  It was better than the DE5000, as expected.
mawyatt:
Any instrument is going to give a different reading in-circuit vs DUT stand alone, simply because the other in-circuit components will draw some amount of residual test current and thus corrupt the in-circuit readings. All the test current is not going thru the intended component in-circuit whereas all the test current travels thru the component stand alone (discounting fixtures, cables and such).

As Tim mentioned we also have the DE5000, and have compared it to our lab grade LCR meters, the Tonghui TH2830 and Hioki IM3536, and it's quite good, compares extremely well, and repeatable. Agree the UI is a little quirky, but for the performance/cost not going to complain!!

The performance/cost is because of the use of a chip-set that takes care of most of the work an LCR needs to perform to make measurements, here if one studies the methods used for the measurements, one can glean quite a bit of understanding and appreciate what's going on and this will directly lead one to better, more reliable measurements.

Best,
TimFox:
What is an in-circuit ESR meter?
Essentially, it applies an AC voltage across two nodes on your PCB, assumes the capacitive reactance at the AC frequency is lower than the ESR, and measures the resulting current.
What can go wrong?
Well, what else is connected across those two nodes in the practical circuit?
Do you know that the impedance of the rest of the circuit at that frequency is much larger than the capacitor's ESR, so the measured voltage is dominated by that ESR?
Could be, in which case the ESR meter gives you a useful indication.
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