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| Brymen 869s DC offset issue when reading ACmV |
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| joeqsmith:
--- Quote from: bdunham7 on January 25, 2022, 05:41:27 am --- --- Quote from: joeqsmith on January 25, 2022, 03:02:04 am ---There's been several what I consider fringe topics like this... Is the claim that the Fluke 189 is without a fringe case? If so, seems like a challenge I could take on... --- End quote --- Well, it is apparently a real use-case and not an unrealistic expectation. The problem is fairly simple though--lack of AC coupling along with an external block not being an adequate fix. We sort of expect AC ranges to work with DC bias, probably because it is easy enough to accomplish--and has been widely implemented. However, if you take a DC reading with a large AC bias, most meters won't handle that very well beyond a certain point and we just accept that as the way things are. I have not been able to find any unexpected fringe case for the F189. --- End quote --- All fringe cases are real use-cases. Everyone who finds one needs it fixed. Every meter with a fringe case is garbage. Other threads covered it. |
| Neutrion:
--- Quote from: bdunham7 on January 24, 2022, 08:34:01 pm --- --- Quote from: Neutrion on January 24, 2022, 08:21:11 pm ---Did by the way anyone tested this scale of the 87V with a DC bias, and for overrange indication? --- End quote --- IIRC yes, but it is AC coupled so there are no surprises there and not a memorable event. You mentioned in another thread that this issue was 'common' and that even many Flukes exhibit it. I can't comment on any that I don't have to test, but I'm not seeing that at all. What might be observed is that some of the Flukes, for example my F116, will appear at first to have an error when you apply a DC bias to an AC signal in the mVAC range. This actually takes effect even at lower signal levels and is not due to overloading. What these meters with DC-coupled mVAC ranges are doing is correctly displaying the TRMS AC+DC value, not just the AC component. That isn't clear just by looking at the meter, so demerits points for that. However, keeping that in mind, I still haven't managed to get any of them to display a 'wrong' reading. It is correct or OL. --- End quote --- In the BM789 topic, what I think you are pointing to,(and the other older topic which I linked in) it was mostly about AC+DCmV capable meters which above a certain point of AC or DC bias, or overloading would read entirely wrong values. Mostly in case of overload. That is what we were discussing 10 pages long last time. :) Unfortunately not even te experts from here were able to come up with an easy to implement Idea, how it could be solved. I suppose from the discussion there, that possibly some extra parallel sampling would be needed only to be able to flag the the overload situation. Or maybe some really smart analogue circuit? To not to talk about reliable ACmv reading with unlimited DC bias on the AC+DCmv scale which seems also like a challenging issue. And yes I remembered wrong, the 87V had it's wrong reading problem in Joe's test(bm789 video) on the DC scale with AC "bias", not the other way around. |
| joeqsmith:
--- Quote from: Fungus on January 25, 2022, 08:46:39 am --- --- Quote from: joeqsmith on January 25, 2022, 03:02:04 am ---Is the claim that the Fluke 189 is without a fringe case? If so, seems like a challenge I could take on... --- End quote --- Or any other Fluke. --- End quote --- You mean like this: https://www.eevblog.com/forum/testgear/brymen-bm789/msg3688948/#msg3688948 That thread had a lot of info for those wanting to read it but obviously it's much easier, maybe more fun to repeat it. Interesting if you read: https://www.eevblog.com/forum/testgear/brymen-bm789/msg3696619/#msg3696619 and https://www.eevblog.com/forum/testgear/brymen-bm789/msg3696679/#msg3696679 Go back a few pages: https://www.eevblog.com/forum/testgear/brymen-bm789/msg3689695/#msg3689695 Specifically: --- Quote ---But then again, I like that low frequency response that I can only get with DC coupling..... Ah the choices we have. --- End quote --- Fun with fringe cases. |
| joeqsmith:
--- Quote from: Neutrion on January 25, 2022, 12:09:50 pm ---And yes I remembered wrong, the 87V had it's wrong reading problem in Joe's test(bm789 video) on the DC scale with AC "bias", not the other way around. --- End quote --- Of course I went after the gold standard of the industry. :-DD |
| Neutrion:
Maybe it's the colour. :) However these days maybe even shining gold would be possible! On the other hand I have to admit that I like the yellow colour of the Fluke too, pity that Brymen chose the red. But it has some positive meaning in buddhist tradition if I remember right. |
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