Uni-T UT181A and calibration - Page 1
Forum section: electronics / testgear

author: Thklinge
author_rank: Newbie
timestamp: October 10, 2018, 03:11:55 am
content: I've got an UT181A and I noticed that VAC seems to be low. Compared to two other DMMs and it is massively off, showing around 206 compared to 228(!!).Since there's no pots inside the 181A to adjust it is there a service menu or is calibration done via software hooked up to a computer? Google didn't seem to have the answer, and no service manual either.

author: skander36
author_rank: Frequent Contributor
timestamp: March 28, 2020, 10:44:29 am
content: Hi Thklinge,Did you manage to find a method for calibration of this multimeter ?Thank you !

author: Thklinge
author_rank: Newbie
timestamp: March 28, 2020, 02:49:33 pm
content: Nope. Uni-T doesn't reply to emails and no one seems to know how to do it. Expensive paperweight...

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2020, 06:10:46 pm
content: I would assume it's a closed case alignment. Too bad UNI-T wouldn't release this information but I can see their point. Every now and then on this site, you will read someone trying to align their meter and basically wanting to return it after they mess it up.I ran into the same problem with Gossen when I tried to find out if their US distributors could align it or it if would have to be returned to the factory. I was hoping they would work with some of the larger calibration labs here in the US.Too bad yours is out. For what it is, I've been pretty impressed with the one I bought.

author: Thklinge
author_rank: Newbie
timestamp: March 29, 2020, 02:53:25 am
content: VAC is out at least. VDC is accurate, as is ohms. But yeah, shame about the VAC and that the factory sends out faulty or not calibrated meters.

author: 2N3055
author_rank: Super Contributor
timestamp: March 29, 2020, 10:39:53 am
content: Quote from: Thklinge on March 29, 2020, 02:53:25 amAre you sure it is out? How do you know? What is the error exactly? How did you verify?UT181A (and pretty much any other meter) has much worse specs for AC. So even if DC V is specced at +- 0,025%+5D, AC (50Hz - 1 kHz) is specced at +-1%+20D.That pretty much means that 1V AC at 50Hz can read from 0,9850 to 1,0150 and be perfectly in spec, meaning no adjustment necessary.There are more than few members here that ruined perfectly good instruments by tampering with it when it wasn't necessary...

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2020, 02:22:24 pm
content: These are the specs from the manual I have for the 181A. So +/- 2.1 assuming they are running at 50/60Hz ish. What they are seeing is more like 22 volts off in this range.QuoteGranted, I assume they are talking volts and they are looking at their AC mains. Hard to believe that the alignment is not automated for these and one would get out not calibrated. Even the worse, bottom end meters I have looked at, all seem to meet their spec when I receive them. Maybe something else is going on.One thing I find odd about the story is you spend say $300 - $400 USD on a brand new meter that doesn't work. Why would you even consider taking it apart? Why wouldn't you return it for a replacement? It's as odd as thinking you're going to align your own meter and not screw it up.

author: skander36
author_rank: Frequent Contributor
timestamp: March 29, 2020, 08:10:47 pm
content: But I don't see why I shouldn't try ...I has buying an CEM 9979 that finally I managed to return it . As a good thing has a calibration function that you can perform manually , and in case that you screw , you can reset to factory calibration .Instead I grab this UNI-T at a good price (232 E) but I want to adjust in some points .For example on 10 volts DC reference that SDM 3065X show as 10.00039 V and Brymen 867s 10.000V, I get 9.997V on UNI-T .5V - 4.99986V - Siglent , 5.000V Brymen and 4.9990 UNI-T2.5V - 2.49848V - Siglent, 2.4985V Brymen and 2.4980 UNI-TVAC - 1.000130 - Siglent, 1.0168 Brymen, 1.0178 UNI-TL.E. - VAC Mains - Siglent 234.5097VAC, 237.41VAC Brymen and 238.31 UNI-TIf for most of this examples the meter is in specs , for 10V DC it can be adjusted ...@Thklinge - On CEM 9979 the calibration function was in menu (Setup) and can be performed with the arrow buttons. Maybe on UNI-T there is a secret combination that show calibration menu.On board there are two ways to talk with the CPU (USB and JTAG) but I don't think that they can be used for calibration . External USB is through IR and I also don't see as a reliable way for calibration ...So why I am thinking at a secret menu ...

author: skander36
author_rank: Frequent Contributor
timestamp: March 29, 2020, 08:22:19 pm
content: And one more thing .I was playing for some time with Fluke 289 but I can't see why I should pay 500 E for it as long as on the market are meters like UNI-T 181A and CEM 9979 . Fluke 289 is not more precise and it has nothing that justify double the price .Personally I think that Brymen is the perfect choice but they have no long logging onboard.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2020, 10:47:05 pm
content: Quote from: skander36 on March 29, 2020, 08:22:19 pmI would imagine for those buying the 289, they need the safety certification, or maybe they need a meter that is more electrically robust. After looking at so many UNI-T products, that's the one thing about them is they have not been very robust. The comments about lack of support from UNI-T may be another reason. For the 181A specifically, I can think of other reasons. Lack of standard batteries. When charging, meter is useless, mechanical parts are not the best quality. The screen is very easy to scratch. I could go on.After seeing a their UT210E switch fail in the last couple of years, I wonder how the 181A's switch would hold up if I were using the meter.Even with it's shortcomings, I do like the meter.

author: Thklinge
author_rank: Newbie
timestamp: March 30, 2020, 06:08:41 am
content: Quote from: joeqsmith on March 29, 2020, 02:22:24 pmI too find it odd that it should be off that much, but compared to other DMMs (including a Fluke) it's way off.I paid 275 usd directly from China. The store put their head in the sand so it's hard returning it. I sent an email to just about every email address on the Uni-T webpages and only the distributor in the Netherlands bothered to answer. They were oblivious to any calibration or service/support. As they said: "we only sell them". Found a re-seller in my country and they wouldn't help since it wasn't bought from them. They suggested a calibration institute so I contacted them and they wanted 100 usd to look at it, 117 usd per hour they work on it and had no idea if they would be able to calibrate it. If they fail they would still be paid.So that leaves me one option: Fix it myself.Quote from: skander36 on March 29, 2020, 08:10:47 pmI also think it would be software-based and in some service menu. I'd be happy to try it except I have no idea how to enter that menu if it exists.

author: skander36
author_rank: Frequent Contributor
timestamp: March 30, 2020, 10:32:42 am
content: Quote from: joeqsmith on March 29, 2020, 10:47:05 pmYou are right ,For companies that base their reputation and certified solutions on tools they used, the price of a Fluke 289 is not a problem . Not talking about of electrical security and serviceability .But for hobbyists and home labs like me those meters offer best ratio value/performance .

author: joeqsmith
author_rank: Super Contributor
timestamp: March 30, 2020, 12:10:43 pm
content: Quote from: skander36 on March 30, 2020, 10:32:42 amIf the switch fails after a couple of years of moderate use like what I am now seeing with the UT210E, $300 for 2-3 years of service is not a very good ratio. I would rather spend $900 and have something that will last 20 years and won't go intermittent. Switch aside, the battery pack which is some non-standard part will eventually fail. I have not been using mine enough to know what it's life will be. Will the hobbyist come up with creative and solutions? My guess is yes. Will some of these make for unsafe conditions? Again, my guess is yes.While you may see it as a good long term investment, I don't.

author: skander36
author_rank: Frequent Contributor
timestamp: March 30, 2020, 01:05:12 pm
content: Quote from: joeqsmith on March 30, 2020, 12:10:43 pmYou make assumptions based on analogies with other models . I also have a UT 61E that has never fail. I use it every day from years. Based on your model of judgement I can assume that UT 181A will last enough to get my money back on it . Also on the reverse I will not credit Fluke 289 based on the many display fading from 87V series for ex. .It carry the Intertek sign so it can be an Intertek product with a higher quality than UT210E .Is about ETL certification fo US. I did not know about .Also battery pack is an Intertek model so it must be found somewhere. But you can use any 7.2V Li-Ion pack of similar size that can be found on the market.Switch seem to be very good built apart from other Uni-T models .For me 20 years is to much for a tool of such complexity (for an axle , a hammer , maybe is useful) . If it will last 5-7 years is OK. Even it will last more, his place will be in personal museum. I like new technologies , new solutions so a long life for such tools is just for brand reputation ...

author: coromonadalix
author_rank: Super Contributor
timestamp: March 30, 2020, 01:23:41 pm
content: The OP need a way to calibrate his meter, its getting off topic ??Maybe find other known meter calibration procedures " if any " with the same dmm chipset

author: skander36
author_rank: Frequent Contributor
timestamp: March 30, 2020, 03:19:21 pm
content: Yeap, slightly offtopic .DMM is using a rather old Cyrustek ES51997 that is used as frontend.The CPU (STMF103) is responsible with calibration process , as on the board cannot be found any trimpot .CEM 9979 use a Hycon DMM frontend with a TI cpu but use also a software calibration with no trimpot onboard .I don't find yet a multimeter with the same architecture .

author: skander36
author_rank: Frequent Contributor
timestamp: March 30, 2020, 04:43:00 pm
content: I found that BK 2712 use the same ES51977 front end but his procedure calibration doesn't seem to be useful . It said that holding MAX/MIN button on start will start calibration mode but this DMM also have a jumper that need to be set for this .

author: skander36
author_rank: Frequent Contributor
timestamp: March 30, 2020, 06:18:04 pm
content: I think I have found a door but we need the key ...Keeping pressed F2 and F3 pres On/Off button.And the screen with a 5 zeros appear . This can be modified with arrows to form a code . 00000 as to CEM is not working ...I will search for key used in other uni-t dmms .

author: joeqsmith
author_rank: Super Contributor
timestamp: March 30, 2020, 10:53:04 pm
content: Quote from: skander36 on March 30, 2020, 01:05:12 pmI am not assuming anything but stating if the meter were to follow suit, it would not be very cost effective. Worse is if it goes intermittent and I don't catch it and start to make bad choices as a result. It's hard to put a price on that.Have you found a battery that was a drop-in replacement? It may be good to know where to buy it from. Someone on this site showed some pictures of their UT181A after they "modified" it to use a different battery.I wonder if the alignment is accessed from the serial interface port. It would make sense that this was automated.

author: skander36
author_rank: Frequent Contributor
timestamp: March 31, 2020, 08:29:42 am
content: A original batery was available here :https://www.aliexpress.com/item/32962838907.htmlNow is no longer available but you can use a Li-Ion battery of your choice :https://www.alibaba.com/product-detail/7-4v-3000mah-polymer-li-ion_62323037244.html?spm=a2700.galleryofferlist.0.0.4949783c5P3568https://www.alibaba.com/product-detail/Wholesale-waterproof-7-4v-3000mah-li_60820035927.html?spm=a2700.galleryofferlist.0.0.4949783c5P3568https://www.alibaba.com/product-detail/Custom-Size-Rechargeable-2S1P-lithium-lipo_60659687786.html?spm=a2700.galleryofferlist.0.0.4949783c5P3568https://www.alibaba.com/product-detail/thin-flat-li-ion-polymer-battery_60771922913.html?spm=a2700.galleryofferlist.0.0.4949783c5P3568That meter was not modified , it was slaughtered . I cannot even watch it .

author: 2N3055
author_rank: Super Contributor
timestamp: March 31, 2020, 09:56:52 am
content: Quote from: skander36 on March 31, 2020, 08:29:42 amBiggest laugh was how guy got pissed when Joe "gently" pointed out what a hack job he did....

author: joeqsmith
author_rank: Super Contributor
timestamp: March 31, 2020, 11:27:25 pm
content: Quote from: 2N3055 on March 31, 2020, 09:56:52 amWas it really all that bad....https://www.eevblog.com/forum/testgear/uni-t-ut181a-pictures/msg746347/#msg746347It was!!!

author: 2N3055
author_rank: Super Contributor
timestamp: April 01, 2020, 12:16:36 am
content: Quote from: joeqsmith on March 31, 2020, 11:27:25 pmUni-Texas chainsaw massacre..

author: CDaniel
author_rank: Frequent Contributor
timestamp: April 01, 2020, 05:38:27 am
content: Sorry to say the obvious but it's a waste of money to buy an expensive Uni-T because it is cheaper than a FlukeFor AC voltage accuracy should be possible to modify some values at the true-rms converter circuit , of course in this case the AC current could be off more or less ...

author: Bobson
author_rank: Regular Contributor
timestamp: July 17, 2021, 08:24:39 pm
content: Quote from: skander36 on March 30, 2020, 03:19:21 pmDo you know how to calibrate 9979? Several years ago I managed to calibrate DC, but I've lost all the knowledge.My 9979 says "offset left right" "key up down", but nothing changes at any range while pressing cursor keys.

author: JulienS
author_rank: Newbie
timestamp: February 25, 2024, 09:49:14 am
content: Quote from: skander36 on March 30, 2020, 06:18:04 pmHi everyone, better late than never ! the key code is 02089.

author: Bobson
author_rank: Regular Contributor
timestamp: June 27, 2024, 05:50:02 am
content: UT-171B to enter CAL mode turn on while pressing RANGE+STORE. Password is the same, 02089.However, unlike UT-181A where you just type in proper values, UT-171B shows some CHANGING value at secondary readout, and it is unclear how to change primary value.

author: stj
author_rank: Super Contributor
timestamp: June 27, 2024, 12:52:32 pm
content: lets apply some logic.the meter is new.it was probably calibrated on an automated system before being packed.it has travelled a long way.i would open it and look for bad soldering or other physical issues.

author: Bobson
author_rank: Regular Contributor
timestamp: June 27, 2024, 06:33:35 pm
content: Quote from: stj on June 27, 2024, 12:52:32 pmHow does it correspond to the adjustment protocol?

author: stj
author_rank: Super Contributor
timestamp: June 29, 2024, 03:07:01 pm
content: it doesnt have anything to do with ajustment protocol.why would you mess up the calibration if it may just be a cracked solder joint?changing the factory calibration should be the very last option, not the first!

author: Bobson
author_rank: Regular Contributor
timestamp: July 23, 2024, 03:39:20 am
content: What made you believe it was the first option?

author: stj
author_rank: Super Contributor
timestamp: July 24, 2024, 12:33:56 am
content: it's the first thing people think of when they get something.

author: sstenks
author_rank: Newbie
timestamp: August 28, 2024, 02:11:34 pm
content: I have the same problem with UT181a with AC voltage it measures 205V on other multimeters 225V ..etcI tried to calibrate the AC voltage but it does not accept the calibration, everything else works DC, A, mA ... how to solve this?Thank you in advance

author: sstenks
author_rank: Newbie
timestamp: August 31, 2024, 12:42:59 pm
content: Hello,Just to let you know that I found a way to successfully calibrate the AC voltage on the UT-181A I will post the details soon and hope it helps whoever needs it. I still can't calibrate the 1000V range but I'm working on it. Thank you all once again for the constructive consideration of the problem, they really complicated it 🙂😊😁

author: janiorib
author_rank: Newbie
timestamp: September 01, 2024, 04:46:48 pm
content: Mine on the 1000 vac scale measured 208 vac on a 220 vac reference, thanks, this post solved my problem, thank you.

author: sstenks
author_rank: Newbie
timestamp: September 01, 2024, 08:08:32 pm
content: Result of today, successfully calibrated range (1000V AC) but not finished it completely. Otherwise, let me say that the ut181a is calibrated at several different frequencies and goes up to 100KHz.Just to add that you will need a function generator to calibrate the AC range, preferably with the highest possible output voltage, in my case it is 20V.It is possible that you will need a function generator amplifier for this job since the sine signal drop quickly above 4Khz and that is only if you decide to go on this adventure.What is important is that for everyday work it is possible to calibrate the AC voltage with the help of a small ordinary transformer using it as an amplifier of the AC signal.To be honest, I doubt anyone will measure 1000V at 100KHz.That's it for now, I'll look at making a little tutorial with pictures after the job is done to make it easier to set up.

author: Taimer81
author_rank: Regular Contributor
timestamp: May 10, 2025, 11:07:48 am
content: Quote from: sstenks on August 31, 2024, 12:42:59 pmHello ! Have you already published the UT181A calibration guide?