Brymen multimeters -  fault? - Page 1
Forum section: electronics / testgear

author: evava
author_rank: Regular Contributor
timestamp: November 23, 2016, 09:31:08 am
content: I wonder if that "discovery" by user hgg in thread "A-look-at-the-uni-t-ut210e" regarding Brymen meters is truth, can someone confirm that (Lightages ?)I dont want cross-link, but I am talking about "Reply #304 on: October 28, 2016, 08:30:20 PM" and following posts (where he shows that mV AC range does not indicate an overload at specific AC signal with DC component).I was sort of before buying BM869s for my Christmas gift, but now I hesitate a little.Would it be possible to fix that eventually by firmware upgrade at home?Or is it not problem at all?

author: IanB
author_rank: Super Contributor
timestamp: November 23, 2016, 09:53:06 am
content: Here is a link to the post I think you are referring to:https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1058296/#msg1058296Every instrument will have some kind of bug or limitation somewhere. If you wait for the perfect meter you will wait forever.In this case the problem seems to be specifically with the AC mV range, on the AC+DC function, with a very particular kind of wave form.Is this a measurement you already make with other meters? If you are now aware of this limitation and so can work around it, would that help you to avoid any misleading measurement results?

author: evava
author_rank: Regular Contributor
timestamp: November 23, 2016, 10:03:10 am
content: https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1058296/#msg1058296

author: 2N3055
author_rank: Super Contributor
timestamp: November 23, 2016, 12:26:10 pm
content: Just buy brymen.. That post is faulty.. Poster seems to not understand correctly TRMS AC and AC+DC .. All is fine...

author: evava
author_rank: Regular Contributor
timestamp: November 23, 2016, 01:09:04 pm
content: Quote from: 2N3055 on November 23, 2016, 12:26:10 pmCan you elaborate on this?Poster maybe understand/ maybe do not understand, but he measures some AC+DC signal, and his two Brymens shows value that is not correct. It would be helpful if he showed screen of his scope with the waveform that he measures by the meters, yes.I have tried this with two mine multimeters that have got AC mA range, and they both showed when out of range. But I have not got any Brymen yet.Otherwise, obviously I see Brymen as fine brand, especially with regards to safety.

author: The Soulman
author_rank: Super Contributor
timestamp: November 23, 2016, 01:29:41 pm
content: Not going to comment on this is a complete fail on the brymens to be able to read the one fineand screwing up the other or a limitation in it's capabilities.In real life this shouldn't be a problem as there isn't much ac with dc-offset around, I can only thinkof audio signals that might have some dc-offset?

author: 2N3055
author_rank: Super Contributor
timestamp: November 23, 2016, 01:44:44 pm
content: I'm at work now will recreate experiment and explain later..

author: rstofer
author_rank: Super Contributor
timestamp: November 23, 2016, 03:04:58 pm
content: Quote from: The Soulman on November 23, 2016, 01:29:41 pmI would think AC+DC would be very common in single rail op amp circuits. It may be possible to measure voltages relative to the virtual ground and this will probably remove the DC component but it should also be possible to measure to the power supply ground.

author: Lightages
author_rank: Unknown
timestamp: November 23, 2016, 03:27:00 pm
content: I am sorry that I didn't follow up on the other thread. I think it best to not pollute the other thread with off subject posts anyway. It is unclear which meters are not reading correctly. I will try to recreate the test conditions again when I have a moment but I am sure that there is no error.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 24, 2016, 04:35:02 am
content: I have not tried to see if the meter detects the over range but assume what the OP wrote is correct in that it does not in the AC only mode. If the DC were enabled, you should see over range on the DC part, telling you to switch it out of the mV range. For me, this isn't a big deal but I could see where for some people this could be a problem.

author: IanB
author_rank: Super Contributor
timestamp: November 24, 2016, 04:56:32 am
content: I assume most of the time when using a meter you would know what kind of voltage to expect before measuring it since you would be checking measurement against expectation.If you didn't know, you would most likely put the meter on autorange and measure AC and DC separately to find out what you are dealing with. That would tell you whether to select the mV or V range for subsequent measurements.

author: evava
author_rank: Regular Contributor
timestamp: November 24, 2016, 09:11:13 am
content: Quote from: joeqsmith on November 24, 2016, 04:35:02 amYes, I realize that it is always wise to check displayed value with other ranges and even switch between AC and DC, and in case inexplicable inconsistencies/discrepancies appears, then is best to check with scope or at least use another device.It is interesting, that e.g. Fluke 87V does not have AC mV range at all (on dial), maybe there is some hitch in implementation that, and this is safe bet ?For example my other meter Minipa ET997TRhttp://www.goodluckbuy.com/minipa-et-997tr-et997tr-3-0-lcd-handheld-digital-multimeter-with-temperature-test.htmldoes not suffer with that(on its separate AC mV range), as well as UT-61e - there is something about meters for $50 range(and they again have theirs "properties"/quirks/odds)

author: 2N3055
author_rank: Super Contributor
timestamp: November 24, 2016, 10:01:04 am
content: RMS is not a real value.. It is a imaginary DC value that would give same thermal equivalent power like the complex waveform you are measuring, if you were to connect them to the same pure resistor (no parasitic inductivity or capacitance).So if you have same sinusoidal waveform with and without DC component, it will greatly differ... Real TRMS is AC+DC.. AC only is not really RMS, except for signals that have no DC component, in which case it is the same... Many TRMS voltmeters don't have AC+DC, only AC RMS, which is not really true RMS measurement.. It is ok if you only want to know AC component...If you are measuring with the scope, and use DC coupling you are measuring AC+DC RMS, with AC coupling, also only AC RMS... So it is easy to have mix of instruments that are not measuring the same thing..Also, you have to keep signal within instruments AD converter range.. so 200mV on top of 10V you measure on 20V range if you are doing AC+DC, or you can measure at 400mV on AC only...You have to understand what are you measuring... That is why we have oscilloscopes, voltmeters alone are not enough to characterize unknown signal..

author: evava
author_rank: Regular Contributor
timestamp: November 24, 2016, 12:40:06 pm
content: Quote from: 2N3055 on November 24, 2016, 10:01:04 amThank you.I'm trying to understand what you're saying.It remains only briefly say why some multimeters (ut61e) show OverLoad, and others not? What is wrong with them, what is so wrong with the signal? Why some cheap multimeters (ut61e) are not confused with the signal?That I do not understand.

author: 2N3055
author_rank: Super Contributor
timestamp: November 24, 2016, 01:52:45 pm
content: Back in the old days instruments were analog and manual. If you connected it wrong..... puuffff... So we where taught propper practice.. If you didn't know what are you measuring start with 1000 V range. And then you lower the range to get better precision if needed.. And also you would try both AC and DC.. Just in case.. The effect could be because meter was put to fixed range, or maybe because it wasn't .. Bottom line, know your instrument, read manual thoroughly,and you'll be fine. Pick a book or two about electrical measurement and start reading.. It's journey not a destination....

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 05:16:48 am
content: That wasn't very useful. Not sure what happened to my post so we will try again...Quote from: evava on November 24, 2016, 12:40:06 pmI don't think there is anything wrong with your signal. I also do not see why ANY meter could not detect if it's ADC is running near it's limit under any of the settings.With the 87V, it does not support the AC+DC mode that I get with the Brymen. You have to read the AC and DC then carry a calculator. I recently picked up a couple of old Fluke 97 scopemeters that can read both the AC and DC simultaneously but it does not have the ability to calculate the AC+DC. I am guessing the square and square root took too much processing. This was part of the reason I have the BM869s. If I ever buy a new Fluke it would be something like the their graphing meter but it would have to be better than they offer now. All beside your point about the over range.Other equipment (scope, SAs) can have similar problems being saturated with no indication. For me, this has never been much of a problem.I have not looked at the Brymen but assume that it can't detect the OR as you mention. I could repeat your test along with checking a few other meters I have but I really am not sure what we would learn. Replicating your results may be good, but I don't doubt what you are seeing. Maybe it would give you a more general idea on if there are other meters that don't always detect when they are out of range. It would be no problem for me to put a 500mV signal on top of what ever bias we want within the limits of the meters.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 05:54:48 am
content: Quote from: joeqsmith on November 25, 2016, 05:16:48 amI think the test to perform would be this:Set the meter on the mV range and select the DC (primary) + AC (secondary) display function.Apply a DC signal within the 500 mV range of the meter, then superimpose an AC signal of varying amplitude, either more or less than 500 mV.Does the meter always display the DC and AC components accurately, or does it give an incorrect reading in either primary or secondary display without indicating OL?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 06:33:40 am
content: As I understand it, the OP is looking for the meters to give them an indication if it is out of range, no matter the mode the meter is in. Idea that the meter should tell you if the reading are inaccurate no matter what you are doing. So AC, AC and DC, AC+DC all should give some indication no matter if it is mv or volts.Some of the meters I have are averaging if we want to run them along with the RMS meters and we want to keep the frequency out of it, just stay with the OP's simple clean sinewave at 60Hz. Not that it's real world... If we agree on some working ranges, multiple people may be able to run separate tests as well. More meters, more data.Should be no problem to set something up if this makes sense.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 06:43:54 am
content: I understand there are many possible variations and combinations, but someone (not the OP) in another thread did a specific test with the BM869s where they used the settings I described. In this test they measured something like a 450 mV AC signal offset by 225 mV (giving a positive waveform varying between 0 mV and 450 mV). In this test the Brymen did not correctly read 450 mV AC in the secondary display and also did not indicate an over range condition.There has been some dispute over whether the meter actually behaves this way or whether there was some kind of experimental error.If you are conveniently able to set up that particular test, it would be interesting to know the results.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 07:39:19 am
content: So 159 AC and 248 DC or 25,281 + 61504 = 86785. Sqrt = 295. Brymen seems to be calculating it right. Seems to agree close enough to sig gen and DSO. Not sure what this problem would have been. Maybe you misunderstood what they asked, or I am misunderstanding what you are asking.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 07:50:07 am
content: Looks good. As it happens I just dragged out some stuff onto my bench and did similar experiments. The Brymen did seem to read accurately, and it did indicate an over range situation in both primary and secondary displays.Let me emphasize I am not asking the question directly, I am just interpreting a question asked by others, and trying to help the OP in this thread. In the other thread linked from the beginning of this thread, one poster said they observed a problem and another poster said this was highly unlikely (neither of whom are the OP, and neither of whom are me).One puzzling observation was that after I had been dialing AC and DC voltages up and down and making the meter indicate OL and come back into range again, I did at one point see the meter reading about 100 mV too low on the DC value. I don't know why it was doing that and the problem cleared after I moved the rotary switch to a different range and back again. Maybe a firmware glitch of some kind? It is hard to say unless I can reproduce it.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 08:21:58 am
content: Sorry, I only ran the settings I thought you were asking for and have not read the other thread. Are you displaying the DC and AC or AC+DC and AC? I trust the Brymen does the calculation correctly as I use it but there could be a problem and I just haven't come across it.So let's push it to just under the limit. 1Vp-p with a 500mV offset. Meter has no problem.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 08:34:05 am
content: Now lets push it over the edge and see if what OP has makes sense...So 1.2Vp-p with a 600mV offset. Should do very nicely. DSO showing 431mV (did not reset stats so ignore) vs 424. Good enough.Now with the BM869s set in ACmv, we see the error. Selecting AC+DC, we see over range. No surprise there but OP is right that the really we know the answer in the ACmv setting will be wrong and the meter does not give any indication.Again, not too surprised by this as this is what I understood OP was seeing. Personally, I don't have a problem with the meter working as it is but I can see this being a trap for some.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 08:34:43 am
content: OK, I have identified a problem. In the first picture the meter is reading a DC voltage with no AC component. It apparently reads accurately.In the second picture there is the same DC voltage, but with an AC voltage added on top. Now the meter is misreading the DC voltage with quite a large error.Maybe you could try the same values and see if you see the same results?

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 08:42:48 am
content: If we drop the AC voltage down a bit, the DC voltage reads correctly again. There seems to be a problem in calculating the DC component when the AC component gets close to or over 500 mV.

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: November 25, 2016, 08:44:11 am
content: Just to add some more data points. I have a Greenlee DM860A, which is a Brymen BM869S, and feeding it a signal from Siglent SDG2042X. I also get accurate results in both windows and get OL for each when the voltage gets too high. On all waveforms frequency is 60Hz.Sorry for the large, craptacular picturesAmplitude 500 mVpp (which would be about 176.5 mVrms)Offset 500 mVDCAmplitude 1000 mVpp (which would be about 353.5 mVrms) - Even here theres no OL on the AC portion because the rms value is still no where near 500Offset 500 mVDCNow switching to having the Sig Gen output mVrms values for the amplitude instead of mVpp.Amplitude 550 mVrmsOffset 500 mVDCAs I bumped up the amplitude, once I hit 550 mVrms the top AC measurement showed OLAmplitude 500 mVrmsOffset 580 mVDCI brought the amplitude back down, then slowly increased the DC offset until the DC measurement showed OL at around 580 mVDC

author: evava
author_rank: Regular Contributor
timestamp: November 25, 2016, 08:58:29 am
content: Gentlemen, thank you all for your efforts!But, see please in original postwww.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1058296/#msg1058296on picture headed with:Quoteand you will see, that user hgg has had dial onmV~, not as you onmV=!On this rangemV~he demonstrates the issue!(false value is displayed on primary display)

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 09:00:52 am
content: I checked the AC voltage and it seems to be correct. Only the DC voltage seems to have the error, and only when the AC voltage is close to or over 500 mV. In the pictures below the AC voltage is below 500 mV and therefore not over range.

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: November 25, 2016, 09:17:06 am
content: I switched it to the other mv AC position and did 2 more measurements. First at 530mVrms, which was accurately measured. Then I bumped it up to 540mVrms and the meter showed OL for the AC measurement. The secondary window in both pictures contains the correct frequency.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 09:19:18 am
content: Quote from: IanB on November 25, 2016, 08:34:43 amYes, I can replicate this no problem and get the same results. Continue to push the offset will result in both AC and DC being wrong in both modes. Again, not a problem for me as I would be looking at the AC DC volt range on it before down switching to at least do a sanity check but there is no reason the meter could not display it was out of range for these cases.

author: evava
author_rank: Regular Contributor
timestamp: November 25, 2016, 09:26:51 am
content: Thank you for your honesty!But, why the user hgg has had displayed0,000Hzthen on secondary display? Another fault when overloaded?

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 09:27:22 am
content: Quote from: evava on November 25, 2016, 08:58:29 amI have tested the AC mV range and I cannot reproduce the problem noted there. Either the meter reads accurately or it reads OL.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 09:36:47 am
content: Quote from: joeqsmith on November 25, 2016, 09:19:18 amI think that in my post #28 above the meter is not technically over range. It is odd that the meter reads incorrectly in the mV range, but it does seem to read correctly in the V range. Is it a hardware problem or a firmware problem, I wonder?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 09:43:33 am
content: May need to go through the zero cross to get the frequency. Fairly common. Meters never seem to make good counters. Switch it to mV DC then enable the counter would have read correct even if it was over driven.Different attenuators for the modes. Makes sense the mV would be wrong and V would be right. Easier to ask Brymen than try and sort it out. I'm just to lazy.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 09:54:51 am
content: Quote from: joeqsmith on November 25, 2016, 09:43:33 amIf you start with a DC voltage of 450 mV and then slowly wind up the AC voltage towards 500 mV, the DC reading remains accurate all the way up to about 490 mV or so, then suddenly drops with a fairly sharp transition. It makes me think of a calculation bug in the firmware.You are right, we have to ask Brymen to give their analysis of this problem. However, until this evening I did not know there was something to ask about.

author: omgfire
author_rank: Regular Contributor
timestamp: November 25, 2016, 10:02:19 am
content: Quote from: CustomEngineerer on November 25, 2016, 09:17:06 amQuote from: hgg on November 15, 2016, 05:58:46 am

author: evava
author_rank: Regular Contributor
timestamp: November 25, 2016, 10:07:01 am
content: And what about Daves BM235?(if someone dares?)QuoteSame firmware bug?

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 10:35:17 am
content: Quote from: evava on November 25, 2016, 09:26:51 amI cannot reproduce the problem reported by hgg. Here is the meter displaying 504 mV AC (and the correct frequency) when superimposed on 380 mV DC. This keeps the entire cycle positive with no zero crossing.

author: Wytnucls
author_rank: Super Contributor
timestamp: November 25, 2016, 01:29:42 pm
content: Quote from: IanB on November 25, 2016, 10:35:17 amVpeak = VRMS × SQRT2 = 504mV x SQRT2 = 712mV-712mV+380mV= -332mVSo, there is zero crossing with your figures.

author: evava
author_rank: Regular Contributor
timestamp: November 25, 2016, 03:47:22 pm
content: We now know that we have to have displayed0,000Hzon secondary display. Then we are sure that there is not any zero crossing.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 03:48:33 pm
content: Put the meter into DCmV and run it up with a DC only source. You will find it reaches the limit at +/-530mVish. Switch it to ACmv and put in a sinewave with no bias and you will find it reaches the limit at 1.5Vp-p or again 530mV RMS. I'm sure there is some headroom in where they set the over range compared with the actual limit of the hardware. If you put the meter into DCmv and show both the AC and DC with 520mVACRMS and raise the bias the meter even to 400mV the DC will already have a small error. Continue to raise the bias to 500mV and both the AC and DC will be off. Continue to raise the bias even higher (about 583mV) and the meter will read roughly 529mVDC. Once you hit that magic 530, it flags the out of range (of course none of the readings the meter is putting out are right).I don't know what it would take to add additional protection to flag it. I guess contact Brymen and get their thoughts.Not sure their threshold for the counter and if they have hysteresis or not. Doubt it is a perfect zero volts. You can bias it to where the meter will not read it in both AC and DCmV settings. Switch to volts and it should pick it up.

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 06:48:00 pm
content: Quote from: Wytnucls on November 25, 2016, 01:29:42 pmOops. I was thinking of the half wave voltage

author: IanB
author_rank: Super Contributor
timestamp: November 25, 2016, 06:54:03 pm
content: Quote from: evava on November 25, 2016, 03:47:22 pmNot quite so, it can display a low AC voltage and 0.000 Hz even when there is a zero crossing, if the DC bias is large enough.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 07:29:49 pm
content: IanB is awake...I don't think it's a question of dare to run Dave's BM235. Just didn't know you were interested.With the BM235, again set to DCmV setting with a DC voltage looks like it over ranges at +/-660mV. When set to ACmV, it over ranges at 1.875Vp-p (again, this is a 60Hz sinewave with no bias). Of course, this is 660mV RMS. No surprise.Applying 659mV RMS with 450mV DC bias, both the DCmV and ACmV appear correct.Increasing the bias to 460mV, the DCmV appears correct and the ACmV is out of range.Now we push it to 656mV of bias and again the DCmV is correct, however the ACmV is no longer showing out of range and the value is incorrect.So, yes it appears to have similar problems. Again, I'm not too surprised as it sounded like someone else had already done the test.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 25, 2016, 08:06:48 pm
content: Pulling out everyone's favorite meter, the UT61E. Keep in mind that mine is now slightly modified.DCmV setting seems to over range around +/-225mV DCACmV will over range around 639mVp-p or again 225mV RMSWith 100mV DC bias and 638mVp-p 60Hz sinewave, both the AC and DCmv readings are correct.Increasing the bias to 200mV, both readings are still correct.Increasing the bias to 226mV causes the DCmV to over range but the AC is still correct.Now as I continue to push the bias higher, the ACmV appears correct.Next I apply 200mV DC if bias and increase the amplitude of the AC signal well outside the range. We start to see the effects on the DC reading. Again, they could have a catch that if the AC component was out of range that the DC would flag an error that it was not correct.Of course driving the meter with 200mVp-p and a 300mV bias, no frequency counter in any of the modes.Guessing other meters will have various problems if I took the time to look at them. For me, not a big deal.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 02:10:28 am
content: Pulled out my favorite meter of all time, the lime green TIP 194 II. Now keep in mind this meter is currently damaged and has high leakage on one of the controllers port pins that effects the resistance measurements.In DCmV the meter over ranges at +/-500mV.In ACmV the meter over ranges at 1.417Vp-p or again 500mV RMS (60Hz sinewave)With 490mVRMS biased with 400mV DC, both the AC and DC millivolts readings are correct.Raising the DC bias to 499.9mV with 490mV RMS applied, the meter provides the correct readings for both.Next I apply 600mV of bias to our 490mV RMS signal and of course the DCmV reading is now out of range. But the ACmV reading is now effected again with no indication that there is a problem. With 1VDC bias the ACmV is all the way down to 374mV.The TPI 194II does support the AC+DC and is a tri-display. But sadly this is not supported in mV ranges. It's too bad I could not get a controller to replace the one on the meter. I would have then attempted to improve it like I show with that low end UT61E.**********************************************************************************************Looking at the Extech EX540In DCmV the meter over ranges at +/-412mV.In ACmV the meter over ranges at 1.168Vp-p or again 412mV RMS (60Hz sinewave)With 409mVRMS biased with 400mV DC, both the AC and DC millivolts readings are correct.Raising the DC bias to 500mV, the meter over ranges on the DCmV but there is a slight effect on the ACmV.With 1VDC bias the ACmV is down to 399mV which is better than the TPI 194 II but it's an error and there again is no indication that there is a problem.This meter also supports AC+DC calculations and appears to show an over range for any combination that goes above 412mV.**********************************************************************************************And I'm sure everyone wants to know the UNI-Ts top of the line UT181A does. Again this meter was damaged like the TPI with one hit from the grill starter. I was able to repair it and made some pretty drastic mods to the PCB. This meter is not original but I do not believe I changed anything that would effect this test.In DCmV the meter over ranges at +/-612mV.In ACmV the meter over ranges at 1.731Vp-p or again 4612mV RMS (60Hz sinewave)With 610mVRMS biased with 600mV DC, both the AC and DC millivolts readings are correct.Raising the DC bias to 700mV, the meter over ranges on the DCmV but the ACmV is correct.With 1VDC bias the ACmV is down to 587mV and again there is no indication that there is a problem.This meter will calculate AC+DC and has a tri-display. In this mode with the same 1VDC bias, the AC+DC and mVDC are both over ranged but the mVAC shows the 587mVAC which is of course not correct. But if the OL were not enough to sway the user into thinking there may be a problem with their measurement, they go one step further and enable the yellow triangle with the lightning bolt. Still, really it's not full proof and the ACmV should show an error as well or you just know someone is going to trust that number...**********************************************************************************************Scott's going to ask about the Fluke 97. That's a special snowflake as it auto ranges both the AC and DC values. You exceed the mV range, it will switch.I don't disagree with the OP that there is a problem with some meters showing inaccurate results under certain conditions without any warning to the user. Hopefully running these few meters shows that this is not something unique to one brand.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2016, 02:29:26 am
content: Quote from: joeqsmith on November 26, 2016, 02:10:28 amSince you have broadened the field to several other meters, this begs the question: what would a bench meter do? Does a typical bench meter have a fundamentally different internal architecture that avoids such limitations, or would it fall prey to similar issues?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 03:24:35 am
content: Quote from: IanB on November 26, 2016, 02:29:26 amMy bench meters are both old from the HP era. These are auto ranging and there is not a separate mV mode. So like my Fluke 97, they will switch.But we can have a little more fun with Fluke. Hate to let them off the hook. The 97 is a little special but let's try 5KY's Fluke 107. This meter has been abused beyond the levels of any meter I have played with. Eventually I damaged it and was able to clean up the mess and replace the failed components but the circuit board is no longer perfect. The meter works fine but I doubt it would handle another 15,000 volt hit.This meter has a mV AC mode. Selecting it and applying our 60Hz sinewave with no bias, it over ranges at about 1.707Vp-p or 600mV RMS.With about 1.557Vp-p or 550mV RMS applied, the meter read 550mV as we would expect. Adding 1VDC of bias, the meter now read 462mV. Again, wrong and there is no indication that it's wrong. Fluke you failed me once again!Really you want a small meter that's robust this thing is going to be hard to beat!*********************************************************************To be fair to Fluke, that 107 is for the Asian market. But I do have a Fluke 115. Good all around meter, nothing special. This meter was never damaged and is unmodified. It has both DC and AC mV ranges.In the ACmV range it can handle around 1.866mVp-p 60Hz sinewave or about 660mV RMS.In the DCmV range it can handle again about 660mV DC.With a 650mV AC RMS signal applied with no bias it of course reads 650mV. Now I add 100mV of DC bias. In DVmV the meter reads 100mV as it should. It's no where near out of range. Selecting the ACmV it reads 657mV. Oops I guess this is wrong! Now if I take the DC bias up higher the ACmV will over range at some point but there is this area where it is giving wrong reading without any indication.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 04:09:35 am
content: Too bad the AM510 and AM530 do not have a separate mV function. Seems Danaher's other divisions should be in on this. Maybe AMPROBE did this for a reason?!But I do have a Fluke 17B+ which also has both AC and DC mV ranges. Again, this meter was damaged and I was able to repair it. There was no damage to the PCB and doubt this test will be effected by anything I have done with it. Overall a decent meter. If it only had TRMS but we are playing with nice clean waveforms now so no big deal. So the first average meter is up to bat...In DCmV the meter over ranges at +/-440mV.In ACmV the meter over ranges at 1.242Vp-p or again 440mV RMS (60Hz sinewave)With 430mVRMS biased with 400mV DC, both the AC and DC millivolts readings are correct.Raising the DC bias to 500mV, the meter over ranges on the DCmV but there is no effect on the ACmV.With 600mV of bias the meter not display over range in the ACmV. The upper left lightning bolt in the LCD is active along with the red backlit triangle with the lightning bolt.Now lets raise the bias even higher. At 900mVDC (again, still our 430mVRMS 60Hz sinewave applied) the both lightning bolts turn back off and all is fine, except the meter is now reading 421mVAC. With the bias increased even further to 1.5VDC, the meter displays 185mVAC!! Shame on you Fluke not telling me something is wrong!!

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 05:01:05 am
content: Got to thinking about it and of course we can force the manual range on the AMPROBE. So I dusted off 5KY's AMPROBE AM530. Again, damaged during my testing but repaired. It's in good shape and don't see a problem with it running this test.So, VAC and manual range to the xxx.x mV scale. Looks like it over ranges at 404mV AC RMS.I apply 380mV AC RMS at 60Hz and add about 1.9VDC of bias. The meter now reads 231mVAC. Seems like an error. I deselect the manual range and it shifts up a range and displays the correct value. I select DC and it displays the correct value. So if the autoscale mode was smart enough to know to shift up a range, why isn't it smart enough to tell me I am over range in manual mode? Another BIG FAIL!

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 05:19:09 am
content: What about Fungus's favorite meter, the Fluke 101? Fungus recommended that meter to me for the very first $50 shoot em up test I ran and it cam out a clear winner. The one I have has never been apart. Not even for a peak! It has survived every thing I have thrown at it to date and works great. It's an averaging meter but again not a big deal for what we are doing. Surely this is our perfect meter!It has a mVAC range and appears to over range at 660.0mV AC RMS 60Hz sinewave. Injecting 1.7VACp-p meter reads roughly 600mV as expected. Adding 300mV DC of bias, the meter reads 13mV high. With 600mV bias, the meter reads 10mV low. At 1VDC bias, its now reading 480mV. At 1.9VDC bias, its all the way down to 85mV and no indication there is anything wrong! Big fail for the Fluke 101!

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 05:38:32 am
content: I do own one meter that does not have a problem with this bias stuff, well at the levels we are playing around with. It's the YX-360TR. This was may be the least amount of money I have spent on a meter next to the free HF ones. The meter was damaged, repaired and then several mods were made to it to attempt to make it more robust. This one is almost bullet proof.Did I mention it is analog?So what makes this meter work. They have a separate physical banana connector just to handle the DC bias case and this input is connected to the main input connector using a film blocking capacitor.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2016, 06:35:10 am
content: Well, I just tried with my HP3456A. It behaves well in all my tests and I cannot find fault with it.If I put it in the 100 mV DC range and feed it 100 mV DC it indicates correctly. If I now add a 1 V RMS AC signal on top the meter shows OL. However, if I switch to the 1 V DC range I again see 0.1 V.Conversely, if I switch to the 1 V AC range and feed it 1 V AC it shows as such. It shows OL if the voltage is increased above 1.2 V.Now if I keep the AC voltage at 1 V and add a DC bias, nothing happens to the AC reading. Even if I add 20 V of DC bias, the AC reading remains unchanged to the full display resolution.So as far as I can tell, the 3456A either shows OL, or it autoranges if enabled, or it shows the correct reading. Nothing I tried could induce it to show an incorrect value on the display.

author: evava
author_rank: Regular Contributor
timestamp: November 26, 2016, 10:34:53 am
content: Oh, it is like detective story, isn't it?Joeqsmith, please please for the last time, Fluke 87V and 289, manual range!

author: Wytnucls
author_rank: Super Contributor
timestamp: November 26, 2016, 11:00:11 am
content: Fluke 185 50,000 count500mV manual rangetest waveform: Sine 480mVAC 9VDC offset 60HzSelection:AC: 487mV 60HzDC: OLAC DC: OL - mVACAC+DC: OL - Hz (60Hz with < 1VDC offset)Auto range mode has no discrepancies:AC: 0.489mV 60HzDC: 09.07VAC DC: 09.04V 00.49VAC+DC: 09.06V 00.00Hz ( 60Hz <4VDC offset)

author: 2N3055
author_rank: Super Contributor
timestamp: November 26, 2016, 11:36:57 am
content: As I said before it is a matter of overloading dynamic range of analog and/or digital path in these instruments..I looked at schematic of Voltcraft 940, similar to UT 71 series... Input goes trough input attenuator and into multimeter chip all DC... there is AD636 TRMS converter that is run as a loopback from the chip itself.. Before AD636 there are two opamps serving as buffers.. On those buffers, there is a switch and DC decoupling capacitor.. This is the place where they decouple, not on the input.So basically, composite signal (AC+DC) goes directly into multimeter chip and is always AC+DC, all the way through the second opamp buffer. Complete signal path before that sees full voltage, AC+full DC offset.(That is exactly the opposite what a good analog meter does.. )So if you apply 200mv 50Hz sine wave with 1V offset, and try to measure it on 400 mV range, you are overloading analog path.. Where exactly it will happen, depends on dynamic reserve of said path..But 9V batteries used and single supply op amps give maybe +-4V, if that.. On 400mV range you're running at 10x amplification, so 400mV overload on input becomes 4V of dynamic range...I didn't look any further and I can't be sure, but I'm guessing majority of multimeters mentioned here has architecture similar to this.. And it's a source of "error" we see here..I agree that it is not best way to do AC/DC switch.. I'm also guessing it was done this way to have guaranteed frequency response (controlled impedances and such).But I know about this, and measure with this in mind.. I think you can confuse any instrument if you try hard enough..

author: Dr. Frank
author_rank: Super Contributor
timestamp: November 26, 2016, 03:27:08 pm
content: The fault of the BM869 in all ACV / DCV modes can be confirmed and also quantified:As the peak voltage (AC + DC) exceeds about 1.095V, an internal amplifier clips the signalwithoutoverload indication, and the TRMS circuit / software creates increasingly high measurement errors, for both the Udc and Uac components of the signal.I made a measurement sequence, using an HP3325B signal generator for ACV plus DC offset at 60Hz, and the BM869 only.I configured the DMM to 5V Udc, DCV and ACV dual display, and the 500mV Udc range likewise.On the 5V range, the DMM would always display correct and precise values, checked by the HP3458A in DCV, ACV and DCV+ACV mode.I compared the 5V range readings with the related 500mV range readings, and calculated the % error between them, and the resulting Vpeak.Errors of about < 0.2 .. 0.4% between both ranges indicate correct readings; this limit is due to the 10 times smaller resolution of the 5V range.Every error above that limit indicates the described clipping effect, which sets in sharply at about 1.10V.In the extreme case of overloading with 0.56Vdc, the DMM still displays no OL, and a really big error of -15% occurs.As you see, the battery was already a bit low at 7V, and 6.2V with lit display.This did not affect the accuracy greatly, though I turned off the light at the crucial limit values.This 1.095Vpeak limit is valid as well for a fresh battery @9.3V.This effect will also appear on higher ranges, I assume. So that's a really bad characteristic of the BM869, to create such gross errors w/o any warning or OL indication.Anyhow, an unknown DC/AC signal can always be analyzed correctly by simply switching to the next higher range.Frank

author: 2N3055
author_rank: Super Contributor
timestamp: November 26, 2016, 05:29:54 pm
content: I did a post earlier but deleted, as it was unclear and convoluted.. I also did some checking with UNi-T 71C, but it doesn't have 500mV AC range.. On 4V no problems, both my siggens couldn't apply enough DC offset to make it go into error..

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 07:35:18 pm
content: Quote from: evava on November 26, 2016, 10:34:53 amNone of this should be a surprise based on the original posts. Well, maybe that Brymen was being isolated for what ever reason. I do not own the meters you mention. Someone else would have to check them.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2016, 07:42:43 pm
content: Quote from: evava on November 23, 2016, 09:31:08 amI think now you have your answer?The problem exists with many meters, not only with Brymen.With knowledge of where and how the problem can occur, you can make sure to avoid it (for example, by always measuring on a higher range first and then down ranging when you know the voltage magnitudes).This would not be a good reason to hesitate about buying a BM869s.

author: Lightages
author_rank: Unknown
timestamp: November 26, 2016, 08:27:08 pm
content: I have emailed my contact at Brymen and I am sure he will respond early next week.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 08:29:45 pm
content: Quote from: IanB on November 26, 2016, 06:35:10 amGood to know. Of course, now I need to run my old bench meter like you asked me to in the first place.This meter is the same one I show in:https://www.eevblog.com/forum/testgear/bm235-variability/Again, bought it brand new from HP and has never been aligned. The DC is effected by the AC level. But the AC is not effected by the DC level.This meter replaced my HP3468A which I also bought brand new from HP with that old HPIL bus. I had it cal'ed in 2002 but it has never been aligned. This meter for what ever reason does not appear to have this problem. In manual range it just over ranges.So the cheapest meter I think I have bought and the most expensive one don't have a problem.I wonder about that HIOKI....

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 08:46:21 pm
content: Looking at my HIOKI DT4252, the AC does not appear to be effected by the DC level but the DCmV measurements can show inaccurate readings. Note that the DCV does not appear to have a problem at least at the levels I have been running at.So my Made in USA old HP meter comes out on top of my heap for this test anyway. Not a bad meter except I was ignorant about HPIB at the time and was not able to predict it's future..Now who is going to call every other manufacture?

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2016, 09:45:39 pm
content: Quote from: joeqsmith on November 26, 2016, 08:29:45 pmOn the 34401A the DC readings are influenced by the amount of AC present?QuoteSo the 3468A behaves better than the 34401A?Which is the most expensive meter, the 3468A or the 34401A? I would have guessed the 34401A to have cost more than the 3468A based on features and year of manufacture.

author: IanB
author_rank: Super Contributor
timestamp: November 26, 2016, 09:48:43 pm
content: Quote from: joeqsmith on November 26, 2016, 08:46:21 pmSeems HP knew what they were doing and made good stuff.The 3456A seems like a very nice instrument, if only it wasn't so damn big! It is hard to call it a bench meter, since it doesn't fit neatly on the average bench (or shelf, for that matter). It is more of a rack meter.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 26, 2016, 10:35:20 pm
content: Quote from: IanB on November 26, 2016, 09:45:39 pmFor the one I own, that appears to be the case. I bought it when they first came out and newer versions may behave differently.QuoteFor this example, would say yes.As for the cost, I would say its a wash. In 92, the 3468A was $820 or $1412 in today's dollars. In 97 the 34401A was $995 or $1498 in today's dollars.Let's contrast that with your 3456A which in 1992 without any options listed at $5696 or $9812 in today's dollars. Would have been just a little overkill for my hobby work back then.

author: evava
author_rank: Regular Contributor
timestamp: November 28, 2016, 09:19:20 am
content: Quote from: IanB on November 26, 2016, 07:42:43 pm+ for complete certainty try even use decoupling capacitor in series with the meter.Thank you all again.That threadhttps://www.eevblog.com/forum/testgear/the-uni-t-ut139c-and-my-power-supply-ripple/concerns probably similar/same issue.It seems, that higher rank Flukes (87V, 185, 189, 289) do not suffer from this issue.In this respect Brymen does not stand out from the crowd of common meters, unfortunately.Price difference tell that.I probably will purchase BM869s, but am a little bit disappointed.

author: IanB
author_rank: Super Contributor
timestamp: November 28, 2016, 10:29:47 am
content: Quote from: evava on November 28, 2016, 09:19:20 amI don't think you should be that disappointed. Every tool has its strengths and weaknesses. It is important to understand that in the real world you cannot achieve something that is ideal in every possible way. There are always practical considerations about what actual hardware can achieve.Let me close by showing you two pictures. I can assure you I am in no way disappointed with how this meter performs.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 28, 2016, 11:30:39 am
content: Quote from: evava on November 28, 2016, 09:19:20 amThey only talk about the 87V and are not specifically looking to see if they can cause the meter to show an invalid result.Do you have data that shows the other meters you mention of "seems" is your feelings about it?

author: evava
author_rank: Regular Contributor
timestamp: November 28, 2016, 04:08:05 pm
content: I do not have any detailed data, my guess is based exclusively on that thread (https://www.eevblog.com/forum/testgear/the-uni-t-ut139c-and-my-power-supply-ripple/and on that post by Wytnucls #56https://www.eevblog.com/forum/testgear/brymen-multimeters-fault/msg1078871/#msg1078871.Yes, I agree with you that it would be more proper for all Flukes to undergo proper investigation like shown by you and others in this thread.I already have asked you, I thought that (after your videos) Flukes 87V and 289 you have at least available from your friends.Thank you in advance!(I learned many things from this thread)

author: joeqsmith
author_rank: Super Contributor
timestamp: November 28, 2016, 05:51:07 pm
content: Quote from: evava on November 28, 2016, 04:08:05 pmOk, it was a guess not a fact. Just wanted to make sure you were not hiding some data on us.

author: Wytnucls
author_rank: Super Contributor
timestamp: November 28, 2016, 05:59:04 pm
content: What data for the Fluke 185 did you not understand?

author: joeqsmith
author_rank: Super Contributor
timestamp: November 28, 2016, 11:25:21 pm
content: Quote from: Wytnucls on November 28, 2016, 05:59:04 pmQuoteI was not sure based on your data that you looked at the DCmV and increased the ACV. You need to check both cases.Quote from: evava on November 28, 2016, 04:08:05 pmThe last 87V has moved from the area but I did talk with the 289 owner...In the mV AC range it over ranges at 1.558p-p or 550mV RMS, again 60Hz sinewaveIn the mV DC range it ORs at 550mV DCWith 500mV AC RMS and up to 4.2VDC bias, there was no effect.With 400mV DC applied and with 5.467Vp-p the meter reads 550mV DC or an error of 150mV. No errors or warnings. I thought this meter wasn't going to have any problems?Now, if you select the AC and DC to enable the spit display (still in mV) the meter displays the correct information. The owner was amazed.***************************************************************************************You asked about the Fluke 189 and while I don't think I know anyone with that meter, I do know someone with a 179 which is a much lower end meter but still a good data point. This meter has a DCmV range but was tested in manual range for ACmV.In the mV AC range it over ranges at 660mV RMS, again 60Hz sinewaveIn the mV DC range it ORs at 660mV DCWith 600mV AC RMS and up to 4.2VDC bias, there was no effect.With 400mV DC applied and with 1Vp-p the meter reads 399.8mV DC.With 400mV DC applied and with 10Vp-p the meter reads 198.7mV DC, about half what it should. Again, no OR error.That's six Flukes I've looked at now that I can cause to read inaccurate without an over range. Too bad not one member is willing to run their 87V to see.

author: evava
author_rank: Regular Contributor
timestamp: November 29, 2016, 01:57:05 pm
content: We started this thread by overloading AC mV range by DC, gradually we moved to overloading DC mV range by AC - interesting.Some meters know how to decouple DC, but "decouple" AC is impossible/much more difficult.Still, real problem is the first, overloading AC mV range by DC. Not problem for higher Flukes.Second problem (overloading DC mV range by big AC) is solvable only by extremely huge dynamic range.(damn it) What prevents all meters from recognizing overload and reporting it?Your outcomes suggest that any meter may be affected, even the big expensive one, only at much higher levels (and thereby less likely to experience).Very interesting.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 30, 2016, 04:17:02 am
content: I thought you just wanted to know if there was any modes where a meter could give inaccurate data without some sort of warning to the user. If we wanted to start adding constraints, seems we missed the point. The meter should always give the correct data or nothing at all with some sort of error.When I ran my old HP which is one of the most expensive meters I have bought for home, I checked it both ways and it had no problems at all. Demand Excellence, Demand HP. Oh yea, I guess you can't anymore. Too bad that little Keysight meter I had with it's fancy GDTs failed during my testing. That was the only Keysight product I have purchased.It will be interesting to hear what Brymen has to say.

author: Dwaine
author_rank: Frequent Contributor
timestamp: November 30, 2016, 08:23:46 am
content: My Agilent U1272a seems off with its values.GeneratorFrequency: 60hzAmplitude: 330.0mVrmsOffset DC: 315.0mVdcU1272a325.40mv AC320.50mv DCAlso, maybe someone can share the secret to posting photos.

author: evava
author_rank: Regular Contributor
timestamp: November 30, 2016, 09:37:56 am
content: Quote from: joeqsmith on November 30, 2016, 04:17:02 amYes, I am happy that you took it in that way. Thank you.

author: cs.dk
author_rank: Unknown
timestamp: November 30, 2016, 09:42:58 am
content: Quote from: Dwaine on November 30, 2016, 08:23:46 am

author: Lightages
author_rank: Unknown
timestamp: November 30, 2016, 01:14:09 pm
content: Here is the response from Brymen:QuoteI can't say that I am happy with this bug, but nothing is perfect I guess. Seeing as it is not the only one to have this problem it seems that it is not easy to get right. It is always a good idea to know the limitations of your tools. It would be nice if these limitations were made known up front.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 01, 2016, 02:01:06 am
content: Quote from: Lightages on November 30, 2016, 01:14:09 pmThanks for taking the time to check into this. Can't say I was expecting much different.I was talking with a friend of mine today and I brought this subject up. Of course the question of starting high and working down came up but I explained that new players may not understand this.After my data dump, I found out he has a Fluke 87 IV and he will run it for us. The best part is this led to a story about how he decides to buy a brand new meter. He has owned the 87 IV for at least 20 years and really likes it. He calls Fluke and they no longer sell it so he decides to get an 87 V. Assuming they are both an 87 so they must be the same thing but the V being newer than IV is all. I then get an ear full of how bad the 87V is (in a little more colorful language) because they don't have all the features he uses with his 87 IV. Why would Fluke call it an 87? Why not a whole new number? After he calms down, he does say the 87V was alright for a basic meter but that he ended up getting a couple of Extechs instead that had the features he uses. Funny stuff.Maybe in a day or two we can add an older Fluke to the mix.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 01, 2016, 02:35:00 pm
content: Quote from: joeqsmith on November 28, 2016, 11:25:21 pmHere are the results for a sine wave of 600mVAC with 9V offset on the 500mV manual range of the Fluke 185:Selection:AC OL 60HzDC OLAC DC - mVdc - mVacAC+DC OL 00.00Hz ( 60.00Hz with <1V offset)No false readings with DC and AC overload on 500mV manual range.With auto ranging, everything is fine:AC 0.611V 60.00HzDC 09.07VAC DC 09.05V 00.61VAC+DC 09.06V 00.00Hz (60.00Hz with <4V offset)The meter was conceived by Tektronix. It sure looks like they knew what they were doing!https://www.eevblog.com/forum/testgear/fluke-185-review/

author: joeqsmith
author_rank: Super Contributor
timestamp: December 02, 2016, 01:31:16 am
content: Quote from: Wytnucls on December 01, 2016, 02:35:00 pmRight, you have ran the low AC with high DC again. Select the DCmV range, apply a bias say 50mV lower than where it over ranges. Now increase the AC level and see of the DC value changes. IMO, it's not a big deal if it does have a problem. Just would be good to know is all.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 02, 2016, 03:59:19 am
content: Right, more testing:DC bias 460mVDCmV manual range:ACmV DCmV100 463.9200 463.9300 464.1400 447.0500 446.0600 446.31000 447.02000 OL

author: joeqsmith
author_rank: Super Contributor
timestamp: December 03, 2016, 05:57:59 pm
content: Quote from: Wytnucls on December 02, 2016, 03:59:19 amThanks. Really, not too bad compared with some of the ones I looked at. I was hunting for the sweet spot when I ran them. I assume your 447 was the worst or that's the limit of the AC sources resolution.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 03, 2016, 10:14:20 pm
content: It is the worst reading. It happens from 390mV up to 1.3V. Above that last AC voltage, the overload (OL) is displayed.Function Gen limit is 6VAC RMS.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 04, 2016, 06:30:29 am
content: The 30,000 count Gossen MetraHit 26S behaves more or less in the same way:With a 280mV offset:On mV DC manual scale, it reads 280mV until AC RMS is raised to 510mV, displaying then 265mV. Above 1.3V AC, it reads a correct 280mV until 1.4V AC, when OL is shown for any higher AC voltage.

author: Wytnucls
author_rank: Super Contributor
timestamp: December 04, 2016, 01:15:26 pm
content: Checked two bench meters (Keithley 2000 and Rigol DM3058E) with the same kind of signals.Again, no dedicated mV range, but tested with manual range selected.A rising DC offset (<9V) with a fixed sine wave voltage elicits a small AC error for both (-3%).An increasing AC sine wave with a fixed DC offset value below the maximum of the mV range causes large increasing DC errors on the Rigol, while the Keithley just goes into overload.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 04, 2016, 03:12:14 pm
content: Good work. Not sure if you are trying to see if they ever under range once they over range. If you look at the Fluke 17B+ for example, it detects the over range but as I continue to drive it harder the over range warnings turns back off and it starts displaying data again. Dave's BM235 did the same thing. You can see these on page 2.I never put more than 10V into the meters and never tried to over drive volts ranges except with the UT90A where it does not have a mV range.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 06, 2016, 01:08:20 am
content: My friend with the 87IV sent me his findings.VACrms Voffset AC Reading Vrms Reading DC (V) Notes0.1 0 0.09997 NA AC mV Scale0.1 1 0.09999 NA AC mV Scale0.1 2 0.09997 NA AC mV Scale0.1 3 0.09996 NA AC mV Scale0.1 4 0.09998 NA AC mV Scale0.1 5 0.09997 NA AC mV Scale0.1 6 0.09998 NA AC mV Scale0.1 7 0.09995 NA AC mV Scale0.1 8 0.09994 NA AC mV Scale0.1 9 0.09993 NA AC mV Scale0.1 9.859 0.09992 NA AC mV Scale0.1 0 0.09987 0 DC or Pulsed mV Scale AC on Main, DC on 2nd0.1 0.5 0.1 0.5010.1 1 0.1001 1.0030.1 1.09 0.1 1.0940.1 1.097 OL OL0.1 0 0.0999 0.00003 DC or Pulsed mV Scale DC on Main, AC on 2nd0.1 0.5 0.0999 0.500850.1 1 0.1 1.00310.1 1.09 0.1 1.09340.1 1.097 OL OLVery impressive but he did not try reading the DCmV with higher AC levels. I did get to hear heard again about how crappy the 87V was by comparison.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 08, 2017, 02:06:03 pm
content: Quote from: evava on January 08, 2017, 08:19:38 amI ran this test with the new CEM DT-9939. In the mVDC mode, it over ranges at 411mV. In the mVAC mode it ORs at 411.49mV.I applied a 400mVDC bias on a 200mVp-p 60Hz sine and the meter reads 70.67mVAC. In mVDC it reads between 397 and 400mV.I continued to increase the AC amplitude to 1Vp-p with the 400mVDC bias. The meter reads 353.28mVAC which is correct. In the mVDC mode it reads between 378mV and OR. So there is some effect to the DC.I tried it with 400mVACrms applied and then pushed the DC bias to 0.993V. The meter reads 411.93, then will OR. So again the DC has some effect on the AC as well. I am not sure why it is better than the EX450.Quote