Products > Test Equipment

Brymen BM789

<< < (33/81) > >>

2N3055:

--- Quote from: bdunham7 on September 19, 2021, 12:36:43 am ---
--- Quote from: floobydust on September 18, 2021, 11:19:36 pm ---For the Brymen and other's using the same chip, you wouldn't have a DC blocking cap. It can't go after the divider chain because well, it's inside the DMM IC. Outside the IC means it's on the hot side side of the divider chain, so a large expensive HV film cap plus another rotary switch contact is required, which costs more.

--- End quote ---


--- Quote from: 2N3055 on September 18, 2021, 11:17:23 pm ---I keep repeating. Yes it will. AC volts is AC coupled.

--- End quote ---

I'm sorry if this seems repetitive or if I've missed something, but I'm not clear on what 'AC coupled' may mean in this case, I haven't seen anyone actually apply the test that I mentioned and in teardowns, I have not seen the HV blocking cap that I would expect.  So perhaps I'm not clear on some aspect of how the meter works.  I'm willing to believe 2N3055 is correct and I'm wrong, but I would like to know where I'm wrong.


--- End quote ---

Well if you put, like I suggested (also repetitively) other meter in set in ohms to input of the meter in question, you will see if input impedance going high, to isolation range. Also, you can take a meter in question, and exactly what was said: you charge meter input wit, say 12V to be safe and discharge it into scope probe set to safe range. If you see exponential decay, there you are you have capacitance.

Also, there is only one way to do it, really. So AC coupled, in this context, means serial capacitor...

joeqsmith:

--- Quote from: Fungus on September 19, 2021, 06:27:13 am ---
--- Quote from: joeqsmith on September 19, 2021, 01:20:47 am ---If you're interested in more details on the 189, I took a quick stab at tracing out this area.   I also made an attempt to look at the current into a short. 

--- End quote ---

Have you painted your 189?

--- End quote ---

This was that meter that I bought to transient test.  You will find my posts on painting it here:

https://www.eevblog.com/forum/testgear/painting-over-rubber/msg1827791/#msg1827791

Over the years, the paint peeled off and you are seeing the primer.  The rubberized paints just don't seem to adhere well in this application.   

joeqsmith:

--- Quote from: AndrewBCN on September 19, 2021, 04:47:23 am ---
--- Quote from: floobydust on September 19, 2021, 04:08:26 am ---
--- Quote from: AndrewBCN on September 19, 2021, 02:56:14 am ---[...] it is clear (to me at least) that among the best practices for DMM usage, shorting the leads before and after any measurement can help avoid some kinds of accidents.
--- End quote ---
NO!!! This is wrong, where did you pick this up from? If the equipment has a charged up DC-blocking cap, it will discharge into the front-end and kill it.

--- End quote ---

 ???

How would a cap that is part of the front-end discharge into the front-end when the leads are shorted?

Joe, we need another video!!!!  :-DD

--- End quote ---

The last video shows me shorting the leads after applying a kV to meter in an attempt to look at the current.   Maybe that's how they design them in Canada.  floobydust would need to provide a brand/model for one that can be damaged as they suggest.      If I have the meter, I would certainly be willing to attempt to replicate their findings.     

joeqsmith:

--- Quote from: bdunham7 on September 19, 2021, 02:57:21 am ---Well, that was easy.  ...

Of course it means that the BM789 also stores device-destroying energy in the AC mode!  :)

--- End quote ---

I could run it up higher if you wanted but would want to make a few changed to my setup just to play it safe.   

Yes, after applying a DC voltage to the 789 while it is in it's ACV mode, I can then discharge the meter to the LED bank and have it light.  I would suggest it stores potentially device-distroying energy.   The parasitics alone may be enough to damage something sensitive.  If you watched that last video, that was basically my point.  This isn't a static problem in the sense that everything is at steady state.   Measuring the DC resistance has little to do with the potential peak currents.   

Fungus:

--- Quote from: joeqsmith on September 19, 2021, 02:28:27 pm ---The last video shows me shorting the leads after applying a kV to meter in an attempt to look at the current.   Maybe that's how they design them in Canada.  floobydust would need to provide a brand/model for one that can be damaged as they suggest.      If I have the meter, I would certainly be willing to attempt to replicate their findings.   

--- End quote ---

Surely the stress of discharging it is no worse than the stress of charging it.

(assuming a low source impedence for charging).

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod