Products > Test Equipment
Brymen BM789
<< < (28/81) > >>
kawal:
Joe
Good video - Didn't realize you can  get a  meter to damage your equipment or give you a shock.  Very informative. 

Kawal
Fungus:

--- Quote from: kawal on September 17, 2021, 05:09:43 pm ---Good video - Didn't realize you can  get a  meter to damage your equipment or give you a shock.

--- End quote ---

Don't worry, I don't think anybody else did either.

(and we're all paranoid now...?)
joeqsmith:

--- Quote from: 2N3055 on September 15, 2021, 01:00:51 pm ---
--- Quote from: AndrewBCN on September 15, 2021, 08:33:31 am ---Let's summarize (again):
1. The OP found a way to "fool" his shiny new Brymen BM789 when set to the DC-coupled high-resolution ACmV range. This basically involves saturating the input circuitry such that the DMM cannot measure the (small) AC component because of a (large) DC bias. Under these conditions the DMM neither detects an overload condition nor provides a correct measurement of the (small) AC component.
2. joeqsmith has demonstrated that a number of different DMMs from different brands can be "fooled" using a similar method.

I think the lesson here, if there is one, is that using a DMM  (any model from any brand) to get correct measurements always involves a minimum of thinking - as 2N3055 reminded us. As well as spending a few seconds to read and understand the User Manual.

Edit: Sorry 2N3055, we seem to have posted our summaries almost simultaneously. I defer to yours which is much better than mine.

Edit2: I can think of a number of reasons why Brymen did not include a series capacitor in the ACmV range front end, and similarly for other DMMs from other brands. But that would be a matter for (reasoned) discussion in another thread, if you ever want to. I for one would be very interested in your opinion.

--- End quote ---

Thank you for the kind words.
I would not mind if you started that discussion, but in my opinion it would necessitate at least partial R.E of front end and switching circuit. Otherwise we would all have many ideas, but no confirmation. I guess Joe did quite some work on that already..
It might even be that meter could be bodged with a capacitor as an afterthought. But I would be very reluctant to do that to my meter and also to publish it on Internet. I have same opinion on that as Joe has about his "hardenings" of various meters. Maybe that is a Pandora box better be left unopened.
Best,

--- End quote ---

I have made my rules about making comments on my YT channel and have filters help the signal to noise ratio.  The rules are of course in the very first post:
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/

Once in a while I still get a few gems from the kiddies.   Attached is a recent post that relates to your comment.  I have removed their name as they run a small channel and see no reason to advertise for them.

They are correct that people continue to ask about my specific mods, even though the rules are clear.  They are also correct that I will normally provide a totally dick response.    I'm amazed that after so many years anyone would expect a different outcome.   

I like the part about having millions of viewers (love that drama), the reality is we are normally talking about a few thousand.   That's already a far larger group than I would expect for such a niche subject.   
 
While the FAQ covers this subject and even includes a few of the earlier like minded comments, my comment about John D. Rockefeller giving stock advice is a case were an ignorant person like our friend here makes a similar request only to file a lawsuit is something people should read about.   From my perspective, there is also a question of being responsible.  The meters being a safety device should not be tampered with.  YouTube may also frown on a channel promoting unsafe behavior. 

The easiest thing for me to do would be to not make any content, but there's a few of you who seem to enjoy it.  So for now, I plan to continue my unfunded, sparse and low quality content.   
2N3055:

--- Quote from: joeqsmith on September 18, 2021, 03:51:28 pm ---
--- Quote from: 2N3055 on September 15, 2021, 01:00:51 pm ---
--- Quote from: AndrewBCN on September 15, 2021, 08:33:31 am ---Let's summarize (again):
1. The OP found a way to "fool" his shiny new Brymen BM789 when set to the DC-coupled high-resolution ACmV range. This basically involves saturating the input circuitry such that the DMM cannot measure the (small) AC component because of a (large) DC bias. Under these conditions the DMM neither detects an overload condition nor provides a correct measurement of the (small) AC component.
2. joeqsmith has demonstrated that a number of different DMMs from different brands can be "fooled" using a similar method.

I think the lesson here, if there is one, is that using a DMM  (any model from any brand) to get correct measurements always involves a minimum of thinking - as 2N3055 reminded us. As well as spending a few seconds to read and understand the User Manual.

Edit: Sorry 2N3055, we seem to have posted our summaries almost simultaneously. I defer to yours which is much better than mine.

Edit2: I can think of a number of reasons why Brymen did not include a series capacitor in the ACmV range front end, and similarly for other DMMs from other brands. But that would be a matter for (reasoned) discussion in another thread, if you ever want to. I for one would be very interested in your opinion.

--- End quote ---

Thank you for the kind words.
I would not mind if you started that discussion, but in my opinion it would necessitate at least partial R.E of front end and switching circuit. Otherwise we would all have many ideas, but no confirmation. I guess Joe did quite some work on that already..
It might even be that meter could be bodged with a capacitor as an afterthought. But I would be very reluctant to do that to my meter and also to publish it on Internet. I have same opinion on that as Joe has about his "hardenings" of various meters. Maybe that is a Pandora box better be left unopened.
Best,

--- End quote ---

I have made my rules about making comments on my YT channel and have filters help the signal to noise ratio.  The rules are of course in the very first post:
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/

Once in a while I still get a few gems from the kiddies.   Attached is a recent post that relates to your comment.  I have removed their name as they run a small channel and see no reason to advertise for them.

They are correct that people continue to ask about my specific mods, even though the rules are clear.  They are also correct that I will normally provide a totally dick response.    I'm amazed that after so many years anyone would expect a different outcome.   

I like the part about having millions of viewers (love that drama), the reality is we are normally talking about a few thousand.   That's already a far larger group than I would expect for such a niche subject.   
 
While the FAQ covers this subject and even includes a few of the earlier like minded comments, my comment about John D. Rockefeller giving stock advice is a case were an ignorant person like our friend here makes a similar request only to file a lawsuit is something people should read about.   From my perspective, there is also a question of being responsible.  The meters being a safety device should not be tampered with.  YouTube may also frown on a channel promoting unsafe behavior. 

The easiest thing for me to do would be to not make any content, but there's a few of you who seem to enjoy it.  So for now, I plan to continue my unfunded, sparse and low quality content.

--- End quote ---

Oh, THAT guy...  hehehe well he doesn't like you, wonder why ... :-DD

Problem is, and nobody wants to hear this, is that you gave enough information to point out in a right direction what you think problem is.. For people that understand what is going on. They have enough info to experiment themselves.
Those that don't know enough to pick up the hints are probably not qualified enough to poke around inside meter.
Even if you publish the schematic and clear photos what needs to be done, will they follow the instructions to the letter?
Will they use same MOVs, PTCs, surge rated resistors, same Corona Dope, or Teflon inserts?
Add to that hordes of people that measure on the secondary of MOT, and then are baffled why the meter is smoking..
I wouldn't want to bear that responsibility. It's called social responsibility.
If people want to walk outside the line, it is their problem and responsibility. I don't want to be enabler.

We had same type of discussion some time ago, when people started promoting that people shouldn't buy cheap scopes from Rigol and Siglent because they figured out how 1000 EDU series from Keysight can be "hacked" and "you get real scope"..
There was heated discussion about it when it was pointed out that "hacking" Keysight scope involved physical removal of components and soldering on the motherboard that not only kills your warranty, but may lead to damaging brand new scope, that still cost more than some very nice scopes from competition. They were making it look simple, but it is not for beginners and people that don't have proper experience and equipment.
We still have few topics here on forum, where people are trying to repair Keysight scopes damaged in attempt to hack it.
Draw your own conclusions..

AndrewBCN:
 ??? It seems I got quoted?  :o

Actually 2N3055 this is what you wrote:


--- Quote from: 2N3055 on September 15, 2021, 08:15:29 am ---...
- Meters SHOULD AC couple in AC only measurements so you could measure 20mV AC riding on top of 100V
- For some reason Brymen doesn't do that on AC mV range. That is NOT good way to do it.
...

--- End quote ---

I believe Brymen does not AC couple the ACmV range because they don't want to have to deal with the kind of accident that Joe has clearly demonstrated can happen if you add a blocking capacitor in your DMM input circuitry, as Fluke did with the 189. It's simpler, safer and cheaper for a DMM manufacturer to just add a note in the User Manual that the meter will not provide a correct reading when the offset + signal > 1000mV, and make that range DC coupled, as Brymen does with most or all of their DMMs. And of course any user that knows a little bit what she/he is doing is going to use an external blocking capacitor when needed and be careful about discharging said capacitor after completing the measurement.

This is what I offered to discuss with you and others in a separate thread, but it seems you somehow misinterpreted my post as me wanting "to open Pandora's box".  :-//
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod