Applent AT826 LCR meter and questions about LCR measurements - Page 1
Forum section: electronics / testgear

author: analogRF
author_rank: Super Contributor
timestamp: July 05, 2017, 02:29:27 pm
content: I am new to this fantastic blog and have only been reading, enjoying, and learning. I cannot thank you guys enough for this blog.I just got a new AT826 LCR meter. This is the first time I am putting my hands on a LCR meter. I have measured L and C in the lab using oscilloscopes and at low frequencies (or measured C using multimeters).The meter looks very nice and of decent quality. Easy to use and easy to go through various options and menus. and you always have all the information on the screen. It comes with two sets of 4 wire kelvin test probes one for SMD and one with alligator clips. They look and feel solid and good quality, too. I will post some pictures later on. It comes with a certificate of quality control (dated June 23, 2017 which was 6-7 days before the item was actually shipped!) and a list of measurements done for quality control (only done just 7 days prior to the item being shipped by the seller on aliexpress!). Anyways, they have measured capacitance and resistance on all frequencies but the table for inductance measurements is only for 1KHz. I dont know why...I do not have many components at hand at this moment and certainly no high accuracy components. However, I measured some ceramic and electrolytic caps (cheap ones) and hand made inductors and now I don't know what I am supposed to trust? Which value am I supposed to pick?I know this has been discussed in the past on this forum and looked them up and i also read the Agilent (Keysight) document on measuring LC. But still I have a couple of questions:If I understand it correctly LCR meters measure the complex impedance and then according to some circuit model for the component they extract the C or L values (and D, Rs, etc...) Obviously this value must be very different with what I get on my multimeter which measures charging time constant for C. However, when I measure such widely different values for a 100nF ceramic cap (albeit a cheap and lossy perhaps) which are very off the mark, too (around 75nF to 87nF on various frequencies) and my multimeter shows 97nF, what am I supposed to do with all these different values? Which one to pick? The situation is a bit better for a hand made air core inductor (around 150uH I hope) because the value changes slightly at various frequencies but still not giving me confidence as to what value to choose! You might say use the frequency that is close to operating frequency, but if my operating frequency is several MHz I have to just throw this LCR meter (and many others) in the garbage bin.Is it reasonable to read such vastly different values for a 100nF or a 10uF (electrolytic) cap for ~0Hz(multimeter), 100Hz, 1KHz,10KHz,100KHz? Their D and Q and ESR values also vary considerably over frequency.As I said this is my first LCR meter and I wanna know if it is actually working correctly. If not, how can I prove it so that I can apply for refund or return (only a limited time left :-( Is this a normal experience for LCR meter owners?Under what conditions am I supposed to read consistent values for C or L at difference frequencies?Your expert help is much appreciated.EDIT: one more closely related questions is this: How can I build (calculate) that equivalent circuit model by doing measurements at let's say 2 or 3 frequencies? What exactly is the circuit model that is used by these LCR meters? Is it just a parallel RC (RL) or a series RC (RL) and that's it? It seems to me that the "resistor" in these models is also a function of frequency, right?

author: analogRF
author_rank: Super Contributor
timestamp: July 20, 2017, 07:35:12 pm
content: 164 reads and not a single reply

author: edavid
author_rank: Super Contributor
timestamp: July 20, 2017, 07:54:43 pm
content: Quote from: analogRF on July 05, 2017, 02:29:27 pmDon't use that type of capacitor where a well defined capacitance is needed.QuoteFor RF inductors, you really need a Q meter or RF impedance meter, not an LCR meter.QuoteYes.QuoteBuy some standards, or use some high quality parts to compare to a friend's lab quality LCR meter.QuoteAir, teflon, polystyrene, polycarbonate caps...

author: analogRF
author_rank: Super Contributor
timestamp: July 20, 2017, 08:03:49 pm
content: Thank you so much for your reply. At least now I know the meter is not giving me crap. since my first post I found somewhat better quality caps (not very good though) and the readings are more consistent, so I know the meter is doing its job properly.One thing about this meter is that when the leads are just lying around on the table, it shows ridiculously high values of L or C randomly (several 1000s of Farads or Henrys! as I move my hands over the probes without touching them I can make those random numbers disappear and meter shows 0 as it should!Is this normal with all LCR meters?one last question: do I need to recalibrate (open/short) every time I change the frequency (not the probes)? or calibrating at one frequency is enough as long as I keep the same leads on? the manual is not clear about that.EDIT: Oh, and I also measured (albeit crudely) the dielectric constant of some cheap FR4 double sided PCBs and I consistently got 4.7-4.8 which I think is OK. That also gave me confidence about the meter.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: July 20, 2017, 09:33:09 pm
content: The manual ought to specify which model (series or parallel) is in use. Parallel is most common, for my meter that is the power-on default but it can be changed.Normally, as well, the calibration is specific to the frequency.Most meters have a way of reading without the four-wire fixture. Use this if you can as it is more accurate.My meter (both portable and bench) do not give wildly different readings on inductance, but I would not care, too much, if nothing is connected. I would, however, try to calibrate the meter using a known inductance. For capacitance, in particular, the stray capacitance with nothing connected varies wildly as you yourself are a capacitor to the meter.Cheap calibration components can be had, if you are sufficiently interested, on ebay. The AT826 supposedly has a basic accuracy of 0.2% which is quite good. If you care about accuracy, though, you will want independent verification.It is true that pretty much all LCR meters only work at certain frequencies. There are usually some known ways to extrapolate out to the MHz range. e.g. for capacitors check the datasheets. The meter gives you the basic data to do this I believe, but this is where I do not have much experience, someone else will need to answer this part of your question.

author: WhichEnt2
author_rank: Regular Contributor
timestamp: July 21, 2017, 12:20:40 pm
content: QuoteElectrolytics is about to lose their capacitance on the 10 kHz and above. Check some datasheets for the electrolytic capacitors, usually dissipation factor measured on 100 or 120 Hz and ESR at about 100 kHz.To check the accuracy you need precision caps and resistors.For exact same purpose I bought some 0.5% polystyrene caps and resistors in 0.1-0.01% tolerance.QuoteIs it covered in the manual?

author: analogRF
author_rank: Super Contributor
timestamp: July 21, 2017, 05:26:29 pm
content: Quote from: RandallMcRee on July 20, 2017, 09:33:09 pmThe series or parallel model can be chosen manually by the user or I can leave it as automatic in which case the meter uses series model when the measured reactance (abs value) is less than 100ohm and uses parallel when the reactance is greater than 100ohmso, you are saying that it must be calibrated each time I change the frequency, right? That's what I thought but the manual is not clear about that.I actually tried to construct that equivalent circuit model by measuring at 4 frequencies (100,1k,10k,100k) once with series and once with parallel modeland I can extrapolate to other frequencies but I have no way of measuring (with reasonable accuracy) at other frequencies. Any advice on that?Of course this simple 2 element model can only work (be valid) way before the first self resonance of the component occurs.

author: analogRF
author_rank: Super Contributor
timestamp: July 21, 2017, 05:32:54 pm
content: Quote from: WhichEnt2 on July 21, 2017, 12:20:40 pmyeah, I am looking at some precision cap/res as standards. Although this meter comes with a calibration certificate (which was dated only a couple of days before my order!) and it comes with a table of measured values at different frequencies showing they are all well within specs...yes, open/shot calibration is done very easily and it stores the parasitics so that the measurements can be compensated. However, it only says repeat the calibration when u change the test leads and does not say whether changing the frequency also requires re-calibration.

author: TurboTom
author_rank: Super Contributor
timestamp: July 21, 2017, 05:51:46 pm
content: The AT826 (at least mine -- bought around two years ago, F/W B2.3) calibrates all measurement frequency ranges at the same time. No need to repeat the open/short calibration everytime the frequency is changed.I found the AT826 to be a pretty capable instrument but you've got to get used to it. Since pure AC measurements may sometimes produce unexpected results, at least compared to what a "classic" DMM will show, there are more things to consider when taking readings. Usually the AT826 is spot-on (except in the 120Hz range, here the tolerance can be a tiny bit higher) but stray effects or core losses in inductors or dielectric losses or other effects usually manifest themselves as ohmic resistance that cannot be measured with a DC signal. Yet, the device under test actually behaves as if there is the read resistance present at that AC frequency.Since measurement current/voltage is rather low, usually non-linear effects cannot be evaluated.Enjoy your new instrument -- I'm sure you will, and all the best,Thomas

author: analogRF
author_rank: Super Contributor
timestamp: July 21, 2017, 06:41:43 pm
content: Thanks, Thomas. It's relief to hear that you are happy with AT826 and it's accurateI paid big $ for this (~$290 shipped via DHL) and it's my first ever LCR meter but I am quite happy with it.This thing can really pick up very small capacitance/inductance. I tried to measure some simple distributed capacitance/inductance made ofFR4 PCB (simple patches and traces) and this thing can measure them (a few pFs and a few nHs !) and measure them quite well!we know how to calculate the values for these stuff and I could verify the measured values, within the tolerance of calculations of course.I know this is not the best way for checking 0.2% accuracy of a meter but gives me confidence about the device.It's interesting that it stores the calibration data for all frequencies at once!I keep calibrating it every time I change the frequency. I think it's a habit I picked up by working with VNA's in microwave/mmwavefrequencies. Over there I have to repeat calibration if I change the frequency span to something that the equipment was not calibrated for.and repeating that calibration is sometimes a pain in the a** but here it's just push of a button, so I kept pushing it

author: tigr
author_rank: Regular Contributor
timestamp: July 21, 2017, 07:14:04 pm
content: This is a good device.You made a good choice.

author: analogRF
author_rank: Super Contributor
timestamp: July 22, 2017, 11:23:35 am
content: Quote from: tigr on July 21, 2017, 07:14:04 pmdo you also get unusually large random values when the test leads are just lying around?thanks!

author: TurboTom
author_rank: Super Contributor
timestamp: July 22, 2017, 01:56:07 pm
content: These huge fluctuations of the readings with the terminals open in inductance and resistance ranges (auto select as well at times) have been criticized for quite a wile but apparently Applent didn't address the issue in later firmware models. Once I contacted Applent support and asked if they would provide firmware updates for the instrument but only got a somewhat surprised reply for what reason I'ld need an update and if I had any "real" malfunction or other problem with the instrument - which I didn't of course....So I just consider the fluctuation of the readings a minor annoyance. Things may be more serious if I would need to use the USB interface to do automated measurements which is easily and comfortably possible with the instrument (btw a big advantage against most of the competitors). Then it may be somewhat troublesome to distinguish between "garbage readings" due to open terminals or a component that's far off tolerance.Whatsoever, I like the AT826 very much, I would appreciate if Applent would take care of these small mentioned shortcomings and publish a firmware update, but other than that I'm really glad I spent a little more initially and didn't get one of the Cyrustek LCR chipset based instruments (even though they probably also do the job okay...).Cheers,Thomas

author: tigr
author_rank: Regular Contributor
timestamp: July 22, 2017, 08:46:02 pm
content: Quote from: analogRF on July 22, 2017, 11:23:35 amIt was not much, but it does not affect the work.

author: sstepane
author_rank: Regular Contributor
timestamp: September 28, 2017, 01:29:44 pm
content: Hi,Just wanted to add my 5 cents - recently got an at826 from Applent. Was trying to use DER DE-5000, but got failing unit - it was measuring way off.I'd say that at826 way better than DE-5000 in terms of useability - very nice clear display, starts quite fast, got very handy and sturdy smd probe and, what is most important to me, allows to select the update speed, so you can actually see if the reading got stable and if it does really measures - on some boards with flux/etc all around small smd part it's hard to say if you got probes into proper contact with the part - with that kind of update you actually are able to say if you're measuring or not.I've got another device from Applent - programmable dc load (at8612) and also very satisfied with that unit - work like a charm. Overall I'd trust Applent in the future - their' devices seem to be well built, precise and of decent quality (I'm not paid by any company).And a little hack - I didn't like the way smd probes were made to stick out from the device to the right side, so I disassembled connector, cut some little plastic and rotated its connecting blade the other way around, so the meter is now to the right of me and short cord of the probe is properly lying straight to it - no loops or whatever it gets curled to (though it's too short, but it's obvious why).

author: cj0
author_rank: Newbie
timestamp: May 12, 2018, 03:33:00 pm
content: Quote from: sstepane on September 28, 2017, 01:29:44 pmAfter readinghttp://www.anbai.cn/products/detail.aspx?familyid=lcr&model=AT826I thought that the Applent AT826 only comes with "ATL501C four-terminal Kelvin test clip" and not with SMD tweezers.How likely is it, when ordering an Applent AT826 that it will come with SMD tweezer probes too?

author: TurboTom
author_rank: Super Contributor
timestamp: May 12, 2018, 08:50:11 pm
content: As far as I know, all the owners got their AT826 with the SMD tweezers included. I've got first-hand experience with three units purchased over the last three years.Cheers,Thomas

author: carl0s
author_rank: Unknown
timestamp: June 27, 2018, 02:54:30 pm
content: Quote from: TurboTom on May 12, 2018, 08:50:11 pmI just bought AT825 from AliExpress seller Shenzhen Measuring Instruments Store, and the SMD tweezers (ATL508B) were not included, even though they were in all the photos on the listing.I contacted the seller and am paying $60usd for them incl shipping, which is less then they usually sell them for.I saw previous spec sheets which said the AT826 includes the SMD fixture and the 824/825 don't. Now it looks like possibly none of them do?