| Products > Test Equipment |
| Brymen BM789 |
| << < (5/81) > >> |
| 2N3055:
--- Quote from: bdunham7 on September 13, 2021, 01:52:32 pm ---The old Fluke 867 Graphing Multimeter could do this, but I can't think of any others. Other than that, the answer to simultaneous DC and ripple measurement is two meters or a 6.5 digit DMM which can measure 10mV on the 100V scale. Or you can just switch back and forth. --- End quote --- That is why I usually simply use BM869S in volt mode most of the time. It has enough resolution to show you milivolts even then.. And if I need more detail, I already know what signal looks like and know mV range will give me no problems. |
| 2N3055:
--- Quote from: Caliaxy on September 13, 2021, 01:52:54 pm ---Well, if this is not a bug and it works as intended, it's a design fail. I replicated the issue on all the Brymen meters within my reach (235, 789 and 689S): AC mV shows nonsensical values in the presence of a high DC offset. The DC offset doesn't have to be huge. I tried 500mV AC on top of a 2V DC offset - something that one would likely encounter in normal everyday life. Other cheap(er) meters (Fluke 101 and 107) do the same (show nonsensical values rather than OL). Daves GW121 does it too. Other even cheaper ones (UT81E and Aneng 8009) don't, they correctly display OL (kudos to them). Fluke 189 (in AC mV) is not tricked by a high DC offset either. Fluke 87V doesn't have this issue at all because it doesn't have a separate AC mV position on the dial in the first place ;D I guess it's one of those situations of "know your meter's shortcomings" and "use it accordingly". Check for DC bias before measuring AC mV. No meter is perfect. Thanks for letting us know! --- End quote --- Are you sure about F87V ? Connect other meter in ohms mode and measure input resistance of F87V. Go through modes and ranges. Not only input resistance won't be constant 10 MOhm, but when it goes Hi impedance then it is AC coupled. If it is DC coupled on mV range, I bet you it can be made to show crap.. Unless they, for some reason, kept 10 MOhm termination and then AC coupled after that. Which would be good design. I wish Brymen did it that way. Longer I have MTX3293, better i like it . It has clear AC only (capacitor coupled), AC+DC, DC (both DC coupled, obviously) and Low Z modes right there and single inputs 100-mV-1000V with distinction that 100mV won't autorange. But BM869S sits right next to it. Fantastic meter, but nothing is perfect. I have few complaints about MT3293 too: - Small fonts on big screen - despite having all the hardware it cannot display AC, AC+DC, DC triple display. Nothing is perfect. |
| bdunham7:
--- Quote from: 2N3055 on September 13, 2021, 02:08:33 pm ---Are you sure about F87V ? Connect other meter in ohms mode and measure input resistance of F87V. Go through modes and ranges. Not only input resistance won't be constant 10 MOhm, but when it goes Hi impedance then it is AC coupled. If it is DC coupled on mV range, I bet you it can be made to show crap.. Unless they, for some reason, kept 10 MOhm termination and then AC coupled after that. Which would be good design. I wish Brymen did it that way. --- End quote --- I don't have the 87V, but my other models actually do keep the 10M (or a little higher on the low ranges--it's not completely constant) resistance in AC mode. This is actually an important feature if you use certain HV probes because otherwise if you were measuring HV AC+DC you might accidentally end up with the entire HVDC component across the blocking capacitor. --- Quote ---it cannot display AC, AC+DC, DC triple display. --- End quote --- My F289 also declines to give me all 3 at once and I think it is because they actually don't have the hardware. I haven't thought about it too hard though.... |
| Neutrion:
--- Quote from: 2N3055 on September 13, 2021, 01:52:22 pm --- He was measuring "more than 1V" with excursions below zero of 100-200 mV. That makes it 1.2-1.3V P-P and right at the saturation point. It had to simply show "OVL" and that is it. When I do the same to BM869S it will show "OVL". But because of DC path, I can inject DC into it and make it go crazy too, with specific values. But it behaves much better. --- End quote --- Yes that is correct up to the limit it was measuring OK the 650mV came somwhere above the limit. But does the 869 correctly shows "OL" for AC in this scenario? Did you try to switch polarity? With the 869 it makes sense to have everything on the same switch position, but with the single display if there is no way to show overrange they certainly could put in a separate AC mV position. --- Quote from: EEVblog on September 13, 2021, 12:47:05 pm --- --- Quote from: Neutrion on September 13, 2021, 11:35:09 am ---And the question is, will it be possible at all to change this in FW. --- End quote --- If it's related to the lack of a DC blocking cap in AC mV mode then there is likely nothing you can in firmware. Dual display meters have a physical DC measurment path a separate AC coupled path, and they get measured separately. --- End quote --- But is also impossible to show somehow that it overranged? Why is that? --- Quote from: Caliaxy on September 13, 2021, 01:52:54 pm ---Well, if this is not a bug and it works as intended, it's a design fail. I replicated the issue on all the Brymen meters within my reach (235, 789 and 689S): AC mV shows nonsensical values in the presence of a high DC offset. The DC offset doesn't have to be huge. I tried 500mV AC on top of a 2V DC offset - something that one would likely encounter in normal everyday life. Other cheap(er) meters (Fluke 101 and 107) do the same (show nonsensical values rather than OL). Daves GW121 does it too. Other even cheaper ones (UT81E and Aneng 8009) don't, they correctly display OL (kudos to them). Fluke 189 (in AC mV) is not tricked by a high DC offset either. Fluke 87V doesn't have this issue at all because it doesn't have a separate AC mV position on the dial in the first place ;D I guess it's one of those situations of "know your meter's shortcomings" and "use it accordingly". Check for DC bias before measuring AC mV. No meter is perfect. Thanks for letting us know! --- End quote --- But if the mentioned meters can also display all the different things on the mV scale just like the Brymen, than it should not be fundamentally impossible to show the fact that it overranged. What causes it with the Brymen? The chipset? The input circuit? And as I said it depends on thefrequency. |
| Caliaxy:
--- Quote from: 2N3055 on September 13, 2021, 02:08:33 pm --- --- Quote from: Caliaxy on September 13, 2021, 01:52:54 pm ---Other even cheaper ones (UT81E and Aneng 8009) don't, they correctly display OL (kudos to them). Fluke 189 (in AC mV) is not tricked by a high DC offset either. Fluke 87V doesn't have this issue at all because it doesn't have a separate AC mV position on the dial in the first place ;D --- End quote --- Are you sure about F87V ? Connect other meter in ohms mode and measure input resistance of F87V. Go through modes and ranges. Not only input resistance won't be constant 10 MOhm, but when it goes Hi impedance then it is AC coupled. --- End quote --- I only meant that Fluke 87V doesn't have an "AC mV" mode on the dial at all, only a "DC mV" one (which has a single 600 mV range). It does measures AC mV in "AC V" mode, which goes down to 600 mV range (and all AC ranges are AC coupled). The lowest DC V range in "DC V" mode is 6 V, hence the separate "DC mV" 600 mV DC mode. Not sure why they did that - maybe it was their way of dodging the bullet. They must have figured the problem and this is how they avoided it. They don't call themselves Fluke for no reason ;D |
| Navigation |
| Message Index |
| Next page |
| Previous page |