Products > Test Equipment
Brymen BM789
<< < (26/81) > >>
joeqsmith:
Thanks for posting.

Not sure off the top of my head how not having the low voltage clamp would ever work in the mVAC mode with a robust handheld meter.   Maybe measure the current through the meter with the mVAC mode selected and look for the knee where the clamp starts to conduct.    Most of handhelds I have are DC coupled and could easily be measured with my bench supply. 

Still, I think we now have our first documented case and I wouldn't be surprised if there were not others.  Recently I had made a video where I used a cheap VNA to make some PDN measurements.   These are normally made with the unit turned off as well as powered up.   The VNA may not like getting exposed to the PDNs voltages, so wideband blocks are added.   You need to be very careful when bringing up the voltages and well as when turning them off.   No big deal for a $50 VNA.  Wouldn't want to tell my boss I damage a quarter million dollar VNA this way.   :-DD
joeqsmith:

--- Quote from: Fungus on September 16, 2021, 05:36:48 pm ---
--- Quote from: joeqsmith on September 16, 2021, 03:23:55 pm ---10nF with a 2kohm source at a kV.... Interesting...

--- End quote ---

Doesn't seem like it could damage much ... but your grill starter has killed a few meters that have some input protection on them (high speed clamps after a protective resistor).

--- End quote ---

Your talking about products that I would expect to be designed to handle some basic transients.  Now I'll certainly be the first to say that not all handheld meters have the same level of robustness.  And yes, there are some down right crap ones that the stupid grill starter with it's what, 5A peak waveform has damaged.     

Here we are talking about the meter becoming the source of the transient and your electronics may not be able to handle the transient it could produce.  I wouldn't be at all surprised if its happened a fair amount and people may not have have understood the cause.    Hard to say.   

Could the free meter from HF be damaged with a Fluke 189, charged to 1.5kV??   :-DD
***
Talk about your fringe case!  :-DD
Fungus:

--- Quote from: joeqsmith on September 16, 2021, 05:52:57 pm ---Could the free meter from HF be damaged with a Fluke 189, charged to 1.5kV??   :-DD
***
Talk about your fringe case!  :-DD

--- End quote ---

It would be interesting to see if any manufacturers have thought about this in their designs. Is this a place where the mighty Fluke can differentiate themselves by having an internal bleeder resister where other manufacturers don't? Will it be the other way around...? :)

If you've got the volts and probes at hand then it's a simple job to charge up a meter then discharge it and look at the waveform.
bdunham7:
I think you'd have to start looking at some schematics to see if this is even a reasonable possibility.  For example, with the (original) F87, if you leave the meter in the AC range you might get, at the very most, a 0.01uF capacitor discharging through about a 10M resistor in parallel with a ~1pF capacitor.  If you switch to any other range, the capacitor is discharged instantly.  I think bench meters with a lower frequency limit, larger blocking caps and a 1M AC input impedance would be more likely to deliver such a jolt, if that is even possible.
joeqsmith:

--- Quote from: Fungus on September 16, 2021, 06:03:10 pm ---
--- Quote from: joeqsmith on September 16, 2021, 05:52:57 pm ---Could the free meter from HF be damaged with a Fluke 189, charged to 1.5kV??   :-DD
***
Talk about your fringe case!  :-DD

--- End quote ---

It would be interesting to see if any manufacturers have thought about this in their designs. Is this a place where the mighty Fluke can differentiate themselves by having an internal bleeder resister where other manufacturers don't? Will it be the other way around...? :)

If you've got the volts and probes at hand then it's a simple job to charge up a meter then discharge it and look at the waveform.

--- End quote ---

Bleed and high impedance don't mix.  Maybe change your habits to discharge the meter.  All these years and still new tricks to learn.   :-DD   

Using a sting of LEDs to look at the waveform as well as conducting the finger test...
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