Uni-t ut61e+ AC input not coupled! - Page 1
Forum section: electronics / testgear

author: nirvana
author_rank: Contributor
timestamp: January 25, 2025, 03:41:44 pm
content: Hi, I have Uni-t ut61e+ multimeter and I have a problem to measuring AC(noise) on DC lines, why AC input not ac coupled, I put cap series and measure correctly, mine is defected or there is no series cap in it, thanks.

author: HKJ
author_rank: Super Contributor
timestamp: January 25, 2025, 05:11:31 pm
content: Quote from: nirvana on January 25, 2025, 03:41:44 pmNot all multimeters has a capacitor in series with the AC input, it is mostly high-end meters that do that.Cheap meters and meters with AC and ACmV position most likely do not.If a meter has a secondary AC on the DC range (In addition to a regular AC position), it will have a capacitor. The AC on the DC switch is for measuring full RMS on any waveform, i.e. both DC and AC component together.

author: nirvana
author_rank: Contributor
timestamp: January 27, 2025, 10:34:54 am
content: thanks for your reply. adding series cap shouldn't be hard. Do you have any suggestions for modding ?

author: Zero999
author_rank: Super Contributor
timestamp: January 27, 2025, 10:54:59 am
content: Presumably you've got it set to AC? Every meter I've used is AC coupled on the AC setting. Even the cheap ones. It's certainly not reserved for the high end models.The manual states it has a low cut-off frequency of 40Hz, in AC mode. Check the settings.https://meters.uni-trend.com/download/ut61b-d-e-user-manual/?wpdmdl=7138&refresh=679647a9368071737901993

author: nirvana
author_rank: Contributor
timestamp: January 27, 2025, 11:08:23 am
content: Measuring AC line with AC, AC+DC or AC lpf mode no problem but I am trying to measure a noise on DC line (I know it's not the right way just looking to make some conclusions) . Yes I see frequency response but I touch any dc line with AC mode meter autorange not working but adding series cap to one probe will measure 0.002mV lpf also measure but with manual ranging. AC+DC mode also not measure correct DC and AC. I think, this meter auto ranging not looking good.

author: Zero999
author_rank: Super Contributor
timestamp: January 27, 2025, 11:23:16 am
content: Perhaps it's the autoranging which is the problem?Set it to AC only, no autorange and it should work.

author: nirvana
author_rank: Contributor
timestamp: January 27, 2025, 11:30:11 am
content: Maybe, I'll put a video later maybe someone found the real problem.

author: 2N3055
author_rank: Super Contributor
timestamp: January 27, 2025, 11:58:42 am
content: Quote from: Zero999 on January 27, 2025, 10:54:59 amNope,He probably used AC mV range that is NOT AC coupled. This meter can measure AC+DC as a single measurement and for that it is DC coupled. Manual states 10 MΩ input resistance, for both V and mV AC ranges.As for autoranging, DC coupled autoranging will autorange to highest voltage it sees. So if you are measuring a 100 mV ripple on top of 100 V, meter will autorange for 100 V.OP needs to connect external capacitor in series with input for this measurement on this meter. I do not recommend trying to redesign meter. Just connect external capacitor when needed.And make sure to discharge it after use.

author: nirvana
author_rank: Contributor
timestamp: January 27, 2025, 12:02:01 pm
content: I tried all mode AC, ACmv or AC+DC, I think sending a video for this problem more understandable.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 27, 2025, 01:33:41 pm
content: Correct. It measures AC+DC. The easy fix, buy the tools for the tasks You need to perform. Or, add an external capacitor. The nice thing about using an external capacitor, You get to choose the type/value. I would never suggest you or anyone else modify a hand held meter.Shown is a high voltage capacitor I use for a DC block. Note the total lack of protection....https://www.eevblog.com/forum/testgear/brymen-bm789/msg3691099/#msg3691099

author: nirvana
author_rank: Contributor
timestamp: January 28, 2025, 10:33:53 am
content: thanks for your reply joeqsmith to ensure my ut61e+ not defected.

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2025, 12:21:24 pm
content: It still seems a bit odd. I haven't used a meter which requires a DC blocking capacitor to measure AC only.I would put a Y2 rated capacitor in a small plastic enclosure with 4mm plug sockets on the front. 1nF will give a low cut-off frequency of 16Hz, if the meter has an input impedance of 10M. That should cover you for voltages up to 500VAC.

author: nirvana
author_rank: Contributor
timestamp: January 28, 2025, 12:26:27 pm
content: measuring AC with DC offset (ex. measuring 20mV AC top off 35Vdc not work without series cap) will confusing autoranging function to determine range.

author: HKJ
author_rank: Super Contributor
timestamp: January 28, 2025, 12:30:06 pm
content: Quote from: Zero999 on January 28, 2025, 12:21:24 pmCheap meters do usually not have capacitors on AC input and with mVAC range you also has a issue with protection: The input impedance drops dramatically above a few volts (The curve is for DC, but AC would be the same without a capacitor):It is usually not fatal to the meter because a PTC resistor will kick in and limit the current.Above curve is from here:https://lygte-info.dk/review/DMMAnengV8%20UK.html

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2025, 01:04:19 pm
content: Quote from: HKJ on January 28, 2025, 12:30:06 pmThen the meter is junk. The correct solution is to buy a decent one.

author: HKJ
author_rank: Super Contributor
timestamp: January 28, 2025, 01:29:27 pm
content: Quote from: Zero999 on January 28, 2025, 01:04:19 pmNot everybody has money or want to use money for one of these:or similar (https://lygte-info.dk/info/DMMHigh-end%20UK.html)And usually the cheap meters measures correctly and are fairly safe when you stay out of industrial or similar energy levels.The cheap meters do have some issues, but then even high end meters have issues (Not the same issues).I could argue the Fluke 289 (A top level meter) is junk, because the display is nearly unreadable, except in bright conditions or with backlight turned one, many cheap meters have MUCH MUCH better displays for reading a measurement.

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2025, 04:03:33 pm
content: A capacitor is cheap.It depends on what you mean by high end?I have an Amprobe 34XRA, which I consider to be mid-range, not high end. I've just tested it with a signal generator and can confirm it blocks DC on the 400mVAC range. I measured the input resistance with another meter. It's about 10M when set to DC and open circuit when set to AC. My only criticism is it could do with more filtering on the DC setting, as the reading wasn't stable when I set the signal generator to 1VDC offset and 2VRMS AC, but on the other hand, that's not bad, since if your DC supply has that much ripple, then there's a fault.https://www.amprobe.com/product/34xr-a/

author: HKJ
author_rank: Super Contributor
timestamp: January 28, 2025, 04:28:55 pm
content: Quote from: Zero999 on January 28, 2025, 04:03:33 pmHigh-end has capacitorMid-range may have capacitorLow-end do not have capacitor.I checked your link for you meter, it is rather badly written.What is a "400 mO" range? I know they mean "Ohm", but why use "mO" or "O" when they can use the micro symbol for current? I am generally to lazy to find the micro or ohm symbol and uses letters instead, but I have never used O or mO for ohm (But I have probably used mhO for conductivity, unit is siemens).

author: 2N3055
author_rank: Super Contributor
timestamp: January 28, 2025, 04:31:12 pm
content: Quote from: Zero999 on January 28, 2025, 04:03:33 pmAmprobe 34XRA is VERY expensive in comparison, 3X more than UNI-T was.. The price difference is 120-130€....

author: joeqsmith
author_rank: Super Contributor
timestamp: January 28, 2025, 05:47:16 pm
content: Quote from: HKJ on January 28, 2025, 01:29:27 pmFunny thing about that photo is the UT181A is not turned on like the others. Possibly a dead proprietary battery and it takes a good day to charge.Not everyone has the money or wants to use money to test these to failure.

author: HKJ
author_rank: Super Contributor
timestamp: January 28, 2025, 06:22:24 pm
content: Quote from: joeqsmith on January 28, 2025, 05:47:16 pmIt is turned on, but the display is a active display and the light cannot match the flashes I used to get the photo.It will probably also be bad to use in direct sunlight. It doesn't matter for me, because I mostly use my meters indoor.Quote from: joeqsmith on January 28, 2025, 05:47:16 pmReplacing a LiIon battery is not that difficult, if you know a bit about electronic. You might loose some capacity because you cannot find the correct size, but have to use a smaller battery, but that is about it.With that said, I do prefer AA/AAA batteries in multimeters, but with that display it will also have issues (Like my CA5293)

author: joeqsmith
author_rank: Super Contributor
timestamp: January 28, 2025, 10:23:15 pm
content: Quote from: HKJ on January 28, 2025, 06:22:24 pmVery easy indeed as was previously demonstrated:https://www.eevblog.com/forum/testgear/uni-t-ut181a-pictures/msg746347/#msg746347

author: 2N3055
author_rank: Super Contributor
timestamp: January 28, 2025, 11:09:17 pm
content: Quote from: joeqsmith on January 28, 2025, 10:23:15 pmAaa, the Texas Chainsaw Massacre meter ..