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| Brymen BM789 |
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| joeqsmith:
--- Quote from: bdunham7 on September 14, 2021, 10:02:06 pm --- --- Quote from: joeqsmith on September 14, 2021, 09:39:33 pm ---Ok, so no luck on your end. All your meters behave as expected while sweeping the frequency, amplitude and offset. Not at all what I would expect but I can try some of my meters and see how they behave. --- End quote --- No, I'm just referring to their ability to withstand without exploding. Getting any of them to read 'wrong' is easy with a combination of high crest factor and offset. I even had my 8846A reading what should be a DC signal as the wrong polarity, until I turned on the analog filter and it started behaving. Finding a signal that baffles something like the F189 but not the the Harbor Freight one is the trick. I'm down to my last HF meter anyway.... Edit: We would have to agree on what the second meter should be so that any results can be replicated. So far, the 8846A has easily been beaten "Harbor Freight freebie outperforms Fluke's best bench meter!" because it starts by default with the analog filter off. A 0-1V 5% 1kHz test signal, which should read ~50mV, is 15.4mV on the 8846A, 46.4mV on the HF. The 46.4mV is more or less correct because if you turn the analog filter on or use a 189/289, that's what you get. I was going to suggest the 189 as the target because you have one and they're well regarded, but I'm finding it very difficult to fool. --- End quote --- I tried a few. The Gossen I have is 300,000 count and there's no mV range. So I can't count that one. 121GW, UNI-T UT61E+, Fluke 107, CEM DT9939 all have problems which I would expect. I'm just using a sine. Again, for me, no big deal. For a list of the meters I still have, you can use the spreadsheet and see beyond the free HF and 189, if we have any other common ground. That or post a list of what you have. --- Quote from: bdunham7 on September 14, 2021, 09:22:34 pm --- --- Quote from: Neutrion on September 14, 2021, 09:03:03 pm ---But I hope to get a more elegant solution. --- End quote --- People have mentioned an external blocking capacitor, but to me that just seems like an opportunity to short something out or get zapped. After all, the reason I have CAT-rated meters, shielded test leaks, insulated alligator clips and so on is to avoid the accidental zapping of either hapless components or myself. So here's an idea! .... --- End quote --- If working in CAT III, I am dealing with AC mains. The meter I use has no mV and clamp inputs. It can't read resistance, capacitance, continuity... I don't go stringing caps around and there would be no reason for it. If the mains start having a DC bias, all hells breaking loose. Still, it would be trivial to mount a cap in an insulated housing with proper connectors. I've never felt the need to do it. *** Added pictures. |
| bdunham7:
--- Quote from: joeqsmith on September 14, 2021, 11:26:19 pm --- That or post a list of what you have. --- End quote --- Other than stuff that can be dismissed as too old (which is most of my stuff including me...) I have a Fluke 116, 189, 289, 323 and 8846A. I also have an HP 34401A, 3478A and several HF-level meters including the free model. That is all unless I've forgotten something. --- Quote ---If the mains start having a DC bias, all hells breaking loose. Still, it would be trivial to mount a cap in an insulated housing with proper connectors. I've never felt the need to do it. --- End quote --- True, but I would think of something mains-derived, like a power supply, where a rectifier failure could change the picture quite quickly. I don't need to do that either because I have meters with their own blocking caps. |
| joeqsmith:
So can I can get the BM789 to read 0 mVAC with a signal applied as I suggested. You bet. Do I care, other than for a small bit of entertainment, not at all. :-DD I could run others but will wait and see what bdunham7 comes up with. |
| AndrewBCN:
--- Quote from: Caliaxy on September 14, 2021, 10:55:14 pm --- --- Quote from: 2N3055 on September 14, 2021, 09:25:06 pm ---And no AC mV range.. That is how Fluke solved that problem with F87V. I prefer to have it, even if it requires thinking when using.. --- End quote --- You got it wrong. Like BM789, Fluke 87V does have an AC 600mV range (and a DC 600mV range), but they are not on the same rotary dial position. The AC 600mV is on the AC V position, which starts auto-ranging from 600mV up, whereas the DC 600mV range has its own rotary dial position, all for itself. The DC V mode starts auto-ranging from 6V up. All AC V ranges (including 600mV) are AC coupled, so the DC offset is irrelevant, unlike in BM789. ... --- End quote --- No, 2N3055 got it right, the AC V position on the Fluke 87V has 6000 count resolution, whereas the separate BM789 ACmV position has 60,000 count resolution. If you use the Auto position on the BM789 it will autorange exactly the same as the Fluke 87V. That means the Brymen has a high resolution, separate dial position for manual range 600mV ACmv which you can choose to use for high resolution ACV measurements - exactly as 2N3055 wrote. And yes, they should add in the BM789 User Manual a warning that this range requires thinking... :-DMM |
| AndrewBCN:
I can see the headlines tomorrow: Electronics Engineer Exposes Major Design Flaw In Hundreds of Multimeters Proves That Most DMMs Cannot Be Used To Measure Ripple And Noise In PSUs |
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