Products > Test Equipment
New UNI-T UT892 2000V AC/DC High Voltage Multimeter
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PartialDischarge:
I don't really see the point, 1) it is not like anyone is going to modify the board and 2) these voltages are 3x..5x times higher than anyone would use this multimeter for.
Also there is a chance that the board is getting punctured since the ground trace runs directly below the input trace and the board is only 1mm thick or so. If this is the case adding silicone or varnish would not help.

I still think that removing the PTC and adding some 100kOhms in there is a nice improvement.
Fungus:

--- Quote from: PartialDischarge on September 11, 2022, 05:44:44 pm ---I still think that removing the PTC and adding some 100kOhms in there is a nice improvement.

--- End quote ---

I still want to know why the PTC is there in the first place. Is it supposed to protect against any arcing that happens before the resistors?
NoMoreMagicSmoke:

--- Quote from: Fungus on September 11, 2022, 06:01:10 pm ---
--- Quote from: PartialDischarge on September 11, 2022, 05:44:44 pm ---I still think that removing the PTC and adding some 100kOhms in there is a nice improvement.

--- End quote ---

I still want to know why the PTC is there in the first place. Is it supposed to protect against any arcing that happens before the resistors?

--- End quote ---

To give reviewers something to point at and say "look at this great input protection. 🤷

PTC will only come into play with enough current to heat them up. If it's arcing before the resistors someone definitely messed up the design. Then again it's Uni-T... It's possible they did mess up the design.
joeqsmith:

--- Quote from: NoMoreMagicSmoke on September 11, 2022, 06:26:49 pm ---
--- Quote from: Fungus on September 11, 2022, 06:01:10 pm ---I still want to know why the PTC is there in the first place. Is it supposed to protect against any arcing that happens before the resistors?

--- End quote ---

To give reviewers something to point at and say "look at this great input protection. 🤷

PTC will only come into play with enough current to heat them up. If it's arcing before the resistors someone definitely messed up the design. Then again it's Uni-T... It's possible they did mess up the design.

--- End quote ---
They may have a spark gap after the PTC on the backside (intentional or otherwise).   Would be interesting to see it all apart.  Maybe they swapped the parts without removing the board. 
Mechatrommer:

--- Quote from: NoMoreMagicSmoke on September 11, 2022, 06:26:49 pm ---
--- Quote from: Fungus on September 11, 2022, 06:01:10 pm ---
--- Quote from: PartialDischarge on September 11, 2022, 05:44:44 pm ---I still think that removing the PTC and adding some 100kOhms in there is a nice improvement.

--- End quote ---
I still want to know why the PTC is there in the first place. Is it supposed to protect against any arcing that happens before the resistors?

--- End quote ---
To give reviewers something to point at and say "look at this great input protection. 🤷
PTC will only come into play with enough current to heat them up....

--- End quote ---
and you will only see that when the dmm breaks down, such as i've mentioned when high energy arcing occured AFTER the PTC. the reason you think its useless being there is because you havent seen its failing in such a manner yet. i dont think UNI-T is fool enough to put $1-5 part just as pure show off. you may argue that it is slow acting in ms range, but few ms second cutoff is better than few seconds of mass slaughter.
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