Handheld LCR Meter - confirming required RMS current to drive test voltage - Page 1
Forum section: electronics / testgear

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 05, 2020, 03:52:13 pm
content: Morning/evening EE & ProfessionalsIn the context of capacitors testing; it is my understanding that lab/benchtop LCR testers comes equipped with ALC (Automatic Level Control) which is meant to supply sufficient current to the DUT. I am wondering: 1) if the common/modern handheld LCR testers have a similar built-in feature and 2) how can we test that they do indeed supply the required Arms current for e.g. capacitors greater than 470uF~1000uF. I've seen quite a few teardowns (thanks @all, btw), and other reviews, however never really seen anyone concluding where those handheld LCR testers limitations are (if any).On the question #2), Is it just a matter of having a Amp meter set-up in series with the DUT during a test and measuring the current?Thanks

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 05, 2020, 04:56:15 pm
content: Well looks like I've answered my own question. Good news is I'm not going to waste time and money on one of those handheld LCR tester and get one with ALC and psu. So be it. Bad news though is... that's going to cost and require quite a bit of additional research :/ So if anyone of you is geared up with the proper lcr test kit already please share model/advantages over another. (my budget <2k). Thanks

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 05, 2020, 07:05:17 pm
content: That claim that the capacitance reading will be low is bullshit , as for all big caps the test voltage will drop to very low levels .For my handheld LCR bridge I measured across 2200uF ~4mV rms at 100Hz. Of course no load level is 600mV .The reason is the shunt in series used for measuring the cap current , so this is absolutly normal .

author: The Electrician
author_rank: Frequent Contributor
timestamp: July 05, 2020, 10:07:04 pm
content: Typically only certain ceramic dielectrics cause a problem. See this video:

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 05, 2020, 10:22:22 pm
content: Even if this is true for other bridges , is showing just about 1uF less ... not a reason to tell a cap is bad . A bridge measures losses too . And I bet that at 100Hz the value would be much closer , 1KHz was chosen just to invent a issue

author: bdunham7
author_rank: Super Contributor
timestamp: July 05, 2020, 10:34:16 pm
content: While the video is technically sound, the point that I think is being overlooked is that this issue only arises in the case of a capacitor that changes value according to voltage. We know about capacitance being specified at a given frequency, thus most halfway decent LCR meters allow you to select the frequency. However, these MLCC caps have their capacitance specified at a certain voltage and frequency--so you need a meter with ALC or you will be reading low. This is not because the MLCC cap has magically superior ultra-low impedance that "drains the meter"--many caps will have ESRs that are much lower than the source impedance of the meter and they measure fine. The issue is that the MLCC cap has a lower capacitance at the lower voltage. Other caps don't do this.It isn't 'large' caps nor an impedance issue--a standard LCR meter will accurately measure capacitors in the many thousands of uF, it is the simple fact that those LCR meters weren't designed to consider the special case of a capacitor that changes capacitance dramatically with voltage.

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 05, 2020, 10:38:11 pm
content: Quote from: CDaniel on July 05, 2020, 07:05:17 pmWhere on earth did you find that sort of high cap MLCC? Max I have here is a 100uF (that does not work, btw lol) and believe we can get some 220uF(max) too. If you are testing a 2200uF electrolytic cap then maybe, but apparently there is just no way to achieve that with higher 1,10,22,33,100uF ect MLCCs using any of those handheld LCR meter :/For obvious reason I can't test that myself, that's why I'm asking you guys. Looking for a lcr test tool that will remain useful in the shop for at least one decade, two preferably.Quote from: The Electrician on July 05, 2020, 10:07:04 pmThanks for that confirmation. That's what my findings initially concluded also. So... on the lookup for a meter ($) that can push up that Vrms to 1V @1Khz. Unless of course those cheap handheld lcr meter can do that? (I'd be surprised, mind you) but worth asking...

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 05, 2020, 11:00:36 pm
content: Good god guys those ALC capable meters are ranging like $6,000~10,000. Branded ones anyway... and 2nd hand ones aren't exactly cheap too. Bet this doesn't not include the kelvin clip/tweesers and other fixtures at that price.Any recommendations?! Happy to dosh out $1,500~2000 (huge max) lol

author: bdunham7
author_rank: Super Contributor
timestamp: July 05, 2020, 11:04:30 pm
content: What are you testing? And why are you testing it (them)?

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 05, 2020, 11:22:37 pm
content: Quote from: bdunham7 on July 05, 2020, 11:04:30 pmMLCCs 3pF~100uF (0402~1206/10). Need precise Z metering tooQuote from: bdunham7 on July 05, 2020, 11:04:30 pmR&D. QC/binning/reliability & prototyping. May perhaps become useful for troubleshooting in the event that...

author: tautech
author_rank: Super Contributor
timestamp: July 05, 2020, 11:26:15 pm
content: Quote from: Mecanix on July 05, 2020, 11:22:37 pmAre the SMD smart tweezer tools not accurate enough ?

author: bdunham7
author_rank: Super Contributor
timestamp: July 05, 2020, 11:34:15 pm
content: Quote from: Mecanix on July 05, 2020, 11:22:37 pmOK. The BK Precision 894 should do what you want for $3800.00 (USD). I don't know of a better option if those are your needs.https://www.bkprecision.com/products/component-testers/894-500khz-lcr-meter.html

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 05, 2020, 11:43:14 pm
content: Quote from: tautech on July 05, 2020, 11:26:15 pmYour guess is as good as mine, never really owned a lcr. Got lots of tweesers thoughLook, I've just found out that those handheld lcr meters won't compensate MLCC's at 1Khz and I wouldn't be surprised to find out they aren't useful or precise at 100/120Hz too. Just don't want to waste time or extra money (that I don't have) getting what will end up being a pita to work with and potentially leaving me guessing whether C/D/Z are withing that 1~2%. Neither I want to get ruined or sucked in that 'marketing testers' business, so that's why I'm asking you guys if there is any "middle option" for technicians like myself (I'm no top gear engineer, far from).Question put simply; what sort of ALC capable lcr meter can < $2000 buy today.Quote from: bdunham7 on July 05, 2020, 11:34:15 pmJust saw your reply as I was typing above. Ok, fair enough... I'll have a look at this and contact them to see if they have a *-25% Off Special" soon! Jeez, that is some serious money just to check on some 1mm parts isn't it lol Thanks

author: bdunham7
author_rank: Super Contributor
timestamp: July 05, 2020, 11:49:33 pm
content: I guess I don't fully understand why you want to know this information to that precision about an inherently imprecise device like the MLCC. Other than someone like a capacitor manufacturer, researcher or an entity with too much money, I don't think most people worry about it simply because AFAIK, you wouldn't use an MLCC if the tolerances were that important. Perhaps I'm wrong about that. The handheld units are perfectly capable of measuring the MLCC accurately, they just don't do it at the level that the parts parameters are specified at.

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 06, 2020, 12:06:53 am
content: Because because because I'm new to this EE world and I have no bloody clue what I "exactly" need for the shop to be self-efficient and backed with the right testers. Last thing I want right now is wasting $10k on a tester that, like you've pointed out, might not be needed for the projects (product-line?) we are aiming at developing between in 2021-2026.I know we need a lcr. Just don't know which one I need. Jugging from the recurrent parts I see in our projects so far (i.e. miniature passives), a lcr that that performs for MLCCs was my first instinct. Just quite shattered to find out they can't handle MLCCs effectively (+ref to Kemet's vid above) but again I'm rather early in my research so who knows...Do you recommend I get one of those cheapo keysight handheld meter (aka U1733C) and start with that and see how it goes?

author: tautech
author_rank: Super Contributor
timestamp: July 06, 2020, 12:17:25 am
content: Quote from: Mecanix on July 05, 2020, 11:43:14 pmI really think you should spend some time looking at what you can buy right on your backdoor.https://www.lcrresearch.com/https://www.smarttweezers.com/These are not toys !

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 06, 2020, 12:23:14 am
content: Quote from: tautech on July 06, 2020, 12:17:25 amMy god, those tweezers!!! The things I could poke with thoseImpressive find, wow is that a welcome to modern year 2020? Soon farewell the fat and expensive testers?

author: tautech
author_rank: Super Contributor
timestamp: July 06, 2020, 12:30:43 am
content: Quote from: Mecanix on July 06, 2020, 12:23:14 amSome of us have been using these for 10+ years and the only way to get them off us is to prize them from our cold dead hands.The now old ST3 tweezers I have get used mainly for TH and faulty component finding and particularly measuring suspect E caps.I wouldn't/couldn't be without a set !Some members here reckon the lcrresearch.com models are better, IDK as no experience with them.

author: bdunham7
author_rank: Super Contributor
timestamp: July 06, 2020, 12:34:53 am
content: I have a BK 885 handheld with kelvin clips and tweezers. I wouldn't even have that if it weren't for the fact that I occasionally want to test in-circuit. This (or the 886) would be the upper limit of what I would recommend anyone buy until they clearly understood the need for something more. A 0.05% bench LCR with features like ALC and DC bias is not typically something you buy just in case you might need it later!

author: Mecanix
author_rank: Frequent Contributor
timestamp: July 06, 2020, 12:45:38 am
content: Quote from: tautech on July 06, 2020, 12:30:43 amNice find. Although I bet they aren't as accurate as my Fluke DMM capacitance setting or my standalone ESR meterNice find none the less, like that product!Right. So I'll hold and reach to those manufacturers and see what's their opinion on that. That vid a few posts above from the folks at Kemet confirms my concerns (worries me in fact) and the main reason I've stopped here today to ask you guys (The Pros). Unless I see some meters demonstrating that they indeed can perform MLCC/DUT equations accurately without an apocalyptic Vrms drop (whether on YT, here on EEV, elsewhere) then I might give that 'handheld' option a try. Might be a reason why nobody is actually advertising that they can MLCC all day long, probably because they can't, who knows.Thanks all. I'll update if I find evidences that this can be performed on a budget (for others to benefit) or let you guys know what I ended up doing to sort out this L/C/R/D/Q/&/whatnot/issue/arggh

author: tautech
author_rank: Super Contributor
timestamp: July 06, 2020, 12:57:20 am
content: Quote from: Mecanix on July 06, 2020, 12:45:38 amYou could be very surprised.I don't even bother grabbing my Fluke DMM when checking caps and just now I measured two 10uF electrolytics ......both close to label value but ESR of 13 and 20 Ohms.The convenience and speed of SMD tweezers is such until you've used a set you'd never know.Do the research and compare datasheets and accuracy specs.

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 06, 2020, 06:39:51 am
content: I wouldn't buy/use those non-linear capacitors , if I forget and put them somewhere in a sensitive part of the circuit not just on power rails ... who knowsMLCC are used for a long time , it's just that type presented in the video .

author: 2N3055
author_rank: Super Contributor
timestamp: July 06, 2020, 11:01:02 am
content: Quote from: Mecanix on July 06, 2020, 12:45:38 amCapacitance measurements on DMMs are utter crap, good only for checking if motor starting capacitors are okayish. Just read the spec. Also, Fluke is not holly cow either, it's not better than cheap Uni T in that regard.Good handheld LCR meters will be 0.2-0.3 % class, and some of the tweezers are even 0.1% class, resolving down to milliohms of ESR.I have old GenRad 1657 RLC Digibridge, UNI-T UT-612, and LCR research Smart Tweezers PRO. Those tweezers also test diodes and LEDS.Digibridge and UNI-T work great for components out of circuits, on PCBs I use tweezers almost exclusively..Digibridge also allows for applying DC bias to a capacitor while measuring..

author: TimFox
author_rank: Super Contributor
timestamp: July 06, 2020, 03:19:27 pm
content: Quote from: CDaniel on July 06, 2020, 06:39:51 amMLCC construction is used on a wide range of dielectric materials: from near-perfect C0G (physically large) to really crappy Z5U. Before MLCC became popular, "ceramic" was demonized by some would did not pay attention to the materials used in "disc" construction. There are legitimate uses for any of these materials, but one must read the data sheet.