Products > Test Equipment
Brymen BM789
bdunham7:
--- Quote from: joeqsmith on September 14, 2021, 11:48:24 pm --- I could run others but will wait and see what bdunham7 comes up with.
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Don't look at me! All I have so far is a Fluke advertisement. I was unable to get any of my meters other than the HF freebie to make an error with this signal (I used 1kHz) They all read correctly up to a point then displayed an overrange indication. Even the CenTech P37772 more or less got it right, however that doesn't have a mVAC range, but it does have 2 VAC. The HF freebie made a similar error at a higher AC voltage, which was needed since its lowest range is 200VAC. You know, since it is intended primarily a mains and service panel meter.
So the goal is to fool a 'good' meter with a signal that the HF meter can read correctly, whether by proper operation or luck. We really need to use the DC ranges, because of the lowest AC range being 200V. I've tried low duty cycle DC pulses, which defeated the 8846A w/o analog filter on, but I have been completely unable to fool the 189, other than going beyond bandwidth (I had a 50Hz 0.01% duty cycle pulse, for example). So if anyone can come up with a signal that the 189 gives a 'wrong' result on in the DC range....
floobydust:
--- Quote from: AndrewBCN on September 15, 2021, 12:21:57 am ---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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Na. We have the technology! Like a built-in IQ test
bdunham7:
--- Quote from: AndrewBCN on September 15, 2021, 12:00:23 am ---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.
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That's preposterous. The bottom 10% of a 60,000 count range is not equivalent to a full 6000 count range, especially when you are talking about TRMS. And the 87V has a 'hi-res' mode, but I don't have one so I can't tell you the details of that. But it's OK to be silly if you like--this is EEVBlog after all.
bdunham7:
--- Quote from: joeqsmith on September 14, 2021, 11:48:24 pm ---So can I can get the BM789 to read 0 mVAC with a signal applied as I suggested.
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So it appears to completely clamped yet using only the calculated AC component to determine whether to display OL, if I'm understanding things correctly. Or did you have to dial that in more carefully? Could you try and replicate the OPs issue? I'd say a 0-1V 50% 200Hz signal and then vary the amplitude up and down and see if you can get it to 'hang' at one value, and if it changes when you swap the leads.
Caliaxy:
--- Quote from: joeqsmith on September 14, 2021, 11:48:24 pm ---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.
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Well, I'm not bdunham7 but, as mentioned in some of my posts above, most of the meters I tried have the same issue: Fluke 101, 107, 17B+, Uni-T UT61e, Agillent U1252A, BM235, BM689S. Fluke 189, 89IV and Agillent U1282A seem to work fine. I don't care much either, but it's good to know. I almost always use an old HP analog meter for AC mV measurements. Overloaded it a few times with voltages higher than the selected range, but its needle is still intact ;D
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