Products > Test Equipment
Brymen BM789
Caliaxy:
--- Quote from: AndrewBCN on September 14, 2021, 05:00:17 pm ---
--- 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 ---
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
--- End quote ---
Thank you for the link. bdundham7 also posted a snapshot of the relevant page of the manual earlier in the thread.
--- Quote from: AndrewBCN on September 14, 2021, 05:00:17 pm ---Pages 26 and 27, if you can only spend 15 seconds to look for the ACmV and AC+DCmV ranges specs.
--- End quote ---
That line in the manual ("Signal peak absolute values, including DC bias, less than 1000mVpeak") does not infer that the meter would display seemingly valid but false values when overloaded. In every single other mode (DC mV included), the meter displays “.OL” when overloaded, hence the reasonable expectation to do so in AC mV as well. Nothing more, nothing less.
Again, I don’t think it’s a big deal if you are aware of it. Many other meters on the market do the same thing.
AndrewBCN:
--- Quote from: Caliaxy on September 14, 2021, 06:42:46 pm ---...
In every single other mode (DC mV included), the meter displays “.OL” when overloaded, hence the reasonable expectation to do so in AC mV as well.
...
--- End quote ---
Unfortunately the "reasonable expectation" argument doesn't work here, for a variety of reasons, but I suggest you read the excellent post by 2N3055, here:
https://www.eevblog.com/forum/testgear/brymen-bm789/msg3686746/#msg3686746
Again, you and the OP are assuming that this was an oversight by the Brymen engineering team, or a bug in the firmware of the BM789. I don't think that's the case at all.
And as has been stated many times: if one so much as spends 45 seconds to read the User Manual and use the DMM accordingly, this issue will never come up.
bdunham7:
--- Quote from: AndrewBCN on September 14, 2021, 07:01:21 pm ---Unfortunately the "reasonable expectation" argument doesn't work here, for a variety of reasons, but I suggest you read the excellent post by 2N3055, here:
Again, you and the OP are assuming that this was an oversight by the Brymen engineering team, or a bug in the firmware of the BM789. I don't think that's the case at all.
--- End quote ---
We're all assuming stuff, 2N3055 included. The 1Vpk limitation is documented. The apparent lack of an overload indication under specific circumstances is not, so why it is that way is unknown. As I said that could be a design issue that Brymen knows about, one they don't know about or a single-unit defect of the OPs meter.
--- Quote ---And as has been stated many times: if one so much as spends 45 seconds to read the User Manual and use the DMM accordingly, this issue will never come up.
--- End quote ---
The whole point of using a meter a good portion of the time is to measure an unknown (to a degree) signal. If you are expecting ~500mV but the meter reads 650mV and the actual voltage is 30V--or 300V--that is at least a glitch. It might also just violate a standard somewhere, but I'm not sure about that.
Fungus:
--- Quote from: AndrewBCN on September 14, 2021, 05:00:17 pm ---even I can understand that this range was *deliberately* not designed to measure ripple and noise from a PSU.
--- End quote ---
I wouldn't use that word for it. I doubr it was a design goal.
I'd say "knowingly". The Brymen engineers did what they could with the chipset and price point they had available.
Anything they couldn't cram in there? They documented it. What else could they do?
It might be possible to make it say 0L, we'll see. I'd bet heavily against them being able to make it measure correctly though.
2N3055:
--- Quote from: bdunham7 on September 14, 2021, 07:16:58 pm ---
--- Quote from: AndrewBCN on September 14, 2021, 07:01:21 pm ---Unfortunately the "reasonable expectation" argument doesn't work here, for a variety of reasons, but I suggest you read the excellent post by 2N3055, here:
Again, you and the OP are assuming that this was an oversight by the Brymen engineering team, or a bug in the firmware of the BM789. I don't think that's the case at all.
--- End quote ---
We're all assuming stuff, 2N3055 included. The 1Vpk limitation is documented. The apparent lack of an overload indication under specific circumstances is not, so why it is that way is unknown. As I said that could be a design issue that Brymen knows about, one they don't know about or a single-unit defect of the OPs meter.
--- Quote ---And as has been stated many times: if one so much as spends 45 seconds to read the User Manual and use the DMM accordingly, this issue will never come up.
--- End quote ---
The whole point of using a meter a good portion of the time is to measure an unknown (to a degree) signal. If you are expecting ~500mV but the meter reads 650mV and the actual voltage is 30V--or 300V--that is at least a glitch. It might also just violate a standard somewhere, but I'm not sure about that.
--- End quote ---
Fact that you cannot pour hydrochloric acid in input sockets is not documented.
Fact that you cannot hit it with a AVe hammer is not documented.
Fact that you cannot plant daisies with it is not documented.
Bad, bad specs...tsk, tsk...
:-//
What is this, McDonalds ? "You cannot pour hot coffee on babies" kind of thing? :-DD
As I said, in a perfect world, it would be nice that if you connect 1000V to mV input, it should not damage it, and then meter should, in a pleasant voice say: "bip. Dear operator.. please make a note that you connected meter to 1000V on a millivolt range. While I was designed to withstand such overload indefinitely, and your safety is not jeopardized, I am unable to measure voltage correctly. Please change input range to volts. Thank you for your cooperation....bip".
Are you kidding me? :palm:
Meter allread has foolproof range designed to completely autorange form 0 to 1000V. It is autoranging volt range. That is the one you use when you don't know what are you measuring. mV range is manual specialized mode for precise measurement that you use only when you know it will be less than 600mV for sure...
That is how you use that meter. Period. Everything else is either lack of knowledge (which is fine, you learn and move on) or deliberate abuse of instrument. Which is also fine if you paid it with your own money. You might as well burn it, see if I care..
But don't expect meter to do anything you want. It is operating outside it's operating envelope. All bets are off.
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