| Products > Test Equipment |
| Brymen BM789 |
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| joeqsmith:
--- Quote from: bdunham7 on September 14, 2021, 04:24:03 pm --- A good challenge might be to come up with a signal that 'good' meters get wrong but the Harbor Freight free one reads correctly. --- End quote --- If you want to play around with it a bit and propose something, I would gladly attempt to follow along. I think the simpler your setup, the better. Using an Arb seems reasonable and allows automation. If you have a way to make a video of it all running, even better. --- Quote from: Caliaxy on September 14, 2021, 04:29:47 pm ---If I understand correctly, the chief complain here is not that the meter cannot measure outside its published specs (DC offset > 1V in AC mV mode), but that it displays erroneous values when this happens (as opposed to "OL"), tricking the unsuspecting user (other people, of course, not us, because now we know it). --- End quote --- I believe this is what the OP is after. Don't get me wrong. I make some pretty boneheaded mistakes but I just don't want the meter to be damaged as a result. |
| Neutrion:
--- Quote from: AndrewBCN on September 14, 2021, 04:12:36 pm ---I have one suggestion for the firmware engineers at Brymen: please program the BM789's MCU to display the following characters when the ACmV or AC+DCmV ranges are selected and an input peak voltage including DC offset > 1000mV is detected: RTFM Honestly, why didn't they think of that? :-DMM --- End quote --- RTFM is also an option, but I still vote for OL. --- Quote from: joeqsmith on September 14, 2021, 04:18:39 pm ---I think the OPs concern is that meters may read what appears to be a normal level. They just want to know that they are out of range without using the ACV or any other mode. Again, just my understanding as I boil these few pages down. --- End quote --- Exactly. And you can say "he". Even without any accurate measurement. |
| AndrewBCN:
--- Quote from: Caliaxy on September 14, 2021, 04:29:47 pm --- --- Quote from: AndrewBCN on September 14, 2021, 04:12:36 pm ---I have one suggestion for the firmware engineers at Brymen: please program the BM789's MCU to display the following characters when the ACmV or AC+DCmV ranges are selected and an input peak voltage including DC offset > 1000mV is detected: RTFM Honestly, why didn't they think of that? :-DMM --- End quote --- If I understand correctly, the chief complain here is not that the meter cannot measure outside its published specs (DC offset > 1V in AC mV mode), but that it displays erroneous values when this happens (as opposed to "OL"), tricking the unsuspecting user (other people, of course, not us, because now we know it). ... --- End quote --- And again, perhaps the unsuspecting user should read the fine manual, which I did even though I don't own a BM789, and it took all of 45 seconds to find the specs. Here: http://www.brymen.com/images/ProductsList/BM780_List/BM789-5-manual-print1-r7.pdf Pages 26 and 27, if you can only spend 15 seconds to look for the ACmV and AC+DCmV ranges specs. --- Quote from: bdunham7 on September 14, 2021, 04:14:03 pm ---... A documented limitation is still a limitation. --- End quote --- You can call it a documented limitation if you want, but - as you yourself noted - the BM789 ACmV range is DC coupled and even though I have an extremely limited understanding of DMM circuitry, even I can understand that this range was *deliberately* not designed to measure ripple and noise from a PSU. Of course I am assuming that Brymen engineers know what they are doing, but that seems like a reasonable assumption. |
| bdunham7:
--- Quote from: AndrewBCN on September 14, 2021, 05:00:17 pm ---You can call it a documented limitation if you want, but - as you yourself noted - the BM789 ACmV range is DC coupled and even though I have an extremely limited understanding of DMM circuitry, even I can understand that this range was *deliberately* not designed to measure ripple and noise from a PSU. Of course I am assuming that Brymen engineers know what they are doing, but that seems like a reasonable assumption. --- End quote --- I'm not sure if we have a linguistic hangup here over the term 'limitation' or what, but I don't see the dispute. If they deliberately design it knowing that it can't do something as a result, then that is a limitation. If they put it in the manual, then it is documented. Neither of these terms is inherently pejorative, simply descriptive. Whether you consider the characteristic (limitation) itself to be a bad thing is up to you. |
| Neutrion:
--- Quote from: AndrewBCN on September 14, 2021, 05:00:17 pm --- And again, perhaps the unsuspecting user should read the fine manual, which I did even though I don't own a BM789, and it took all of 45 seconds to find the specs. Here: http://www.brymen.com/images/ProductsList/BM780_List/BM789-5-manual-print1-r7.pdf Pages 26 and 27, if you can only spend 15 seconds to look for the ACmV and AC+DCmV ranges specs. --- Quote from: bdunham7 on September 14, 2021, 04:14:03 pm ---... A documented limitation is still a limitation. --- End quote --- You can call it a documented limitation if you want, but - as you yourself noted - the BM789 ACmV range is DC coupled and even though I have an extremely limited understanding of DMM circuitry, even I can understand that this range was *deliberately* not designed to measure ripple and noise from a PSU. Of course I am assuming that Brymen engineers know what they are doing, but that seems like a reasonable assumption. --- End quote --- Please RTFFP I could say: "I know that I should use the higher ranges for signals like this, but when someone measures a lower level signal, and it raises up above the limit, there is no way of knowing it, you just stop seeing anything above this level, while the voltage might be skyhigh. I can not test it with higher voltages unfortunately, but would be nice if someone could do that. So I am not vorrying about accuracy above the specified limit, but about the fact that it does not show overrange on the AC scale." It is NOT documented however, that the meter can not show that it overranged on the AC scale under certain circumstances. (We still don't know whether this is also the case with simmetrical signals or not.) |
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