Products > Test Equipment
New UNI-T UT892 2000V AC/DC High Voltage Multimeter
Gyro:
--- Quote from: PartialDischarge on September 08, 2022, 06:52:38 pm ---The case has a big lip + the outer silicone cover. If you are worried about that I’d simply put silicone over the string. Also the mod that I did makes it safer since now there is 800kohm right after the jack.
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No critisism, just interested in how / why they've implemented things.
Fungus:
--- Quote from: PartialDischarge on September 08, 2022, 06:52:38 pm ---The case has a big lip + the outer silicone cover.
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Yep, you're in much more danger from holding the probes than from anything that might jump out of the case.
As noted though, it's an obvious fix and would have cost them nothing.
--- Quote from: Gyro on September 08, 2022, 06:54:46 pm ---
--- Quote from: Fungus on September 08, 2022, 06:42:48 pm ---Measuring the voltage at the output of a Cockroft-Walton generator can be delicate work.
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That's when it's a good time to build an external 100M+ divider (that's what we in the 20K Ohms-per-Volt club would do!)
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You still need a very high impedance meter to measure the voltage.
(eg. A Fluke 8060A - is there anything that meter doesn't do well?)
Mechatrommer:
--- Quote from: PartialDischarge on September 08, 2022, 05:59:57 pm ---So I decided to modify the meter, since I don't know how good those 2.5M resistors are, I replaced them with 2.4M ones that I have. Also I removed the PTC and put there the rest of the resistance minus a bit to compensate for the low 0.2% reading. Now it is measuring +-1V.
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there you go a high voltage nuttery genius came to play clever than the designer... you just replaced 4 digit (more precise) resistors with cheaper 3 digit batch, how well you know your 2.4M batch? do they cost like $1 each? with rubbery stuffs surrounding their pins? and rated 2KV each? 8x of normal 0805 or 1206 is good for 1.2-1.6KV isolation theoritically (physically) https://www.vishay.com/docs/28705/mcx0x0xpro.pdf, there are more components downstream to provide extra isolations. and you just replaced a probably $1-5 PTC part that probably can save the DMM's or yours ass in case of downstream breakdown with $0.01 parts that provide no protection at all and much higher dielectric breakdown risk. you've probably screwed the factory's hygienic grade too.
btw for those who asked why those dividers are so to the side, with concern that they are near to the user's side (with lips and extra rubber holster as isolation, wouldnt that be enough?). well i can think of that... creepage on pcb is real, and moving them closer to other components will increase risk of that, since they want to cheap out by not making extra costly slots between them. so they can achieve $40 price point that beginner users love. ymmv. https://www.tempoautomation.com/blog/understanding-pcb-creepage-and-clearance-standards/
PartialDischarge:
--- Quote from: Mechatrommer on September 08, 2022, 11:11:07 pm ---
--- Quote from: PartialDischarge on September 08, 2022, 05:59:57 pm ---So I decided to modify the meter, since I don't know how good those 2.5M resistors are, I replaced them with 2.4M ones that I have. Also I removed the PTC and put there the rest of the resistance minus a bit to compensate for the low 0.2% reading. Now it is measuring +-1V.
--- End quote ---
there you go a high voltage nuttery genius came to play clever than the designer... you just replaced 4 digit (more precise) resistors with cheaper 3 digit batch, how well you know your 2.4M batch? do they cost like $1 each? with rubbery stuffs surrounding their pins? and rated 2KV each? 8x of normal 0805 or 1206 is good for 1.2-1.6KV isolation theoritically (physically) https://www.vishay.com/docs/28705/mcx0x0xpro.pdf, there are more components downstream to provide extra isolations. and you just replaced a probably $1-5 PTC part that probably can save the DMM's or yours ass in case of downstream breakdown with $0.01 parts that provide no protection at all and much higher dielectric breakdown risk. you've probably screwed the factory's hygienic grade too.
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Lol, I was expecting this kind of comment. I’m not going to explain you anything cause you like to assume and it seems that already know everything, let me just tell you that I design electronic HV stuff for power distribution, and I mean up to 36kV not the 200V people usually refer to HV. You haven’t even noticed what my username means, cause well you don’t know much about HV. Well you also haven’t even noticed that I took 40k off of the resistive string and are telling me about the precision of the resistors :palm:
Mechatrommer:
--- Quote from: PartialDischarge on September 09, 2022, 03:04:02 am ---...let me just tell you that I design electronic HV stuff for power distribution, and I mean up to 36kV not the 200V people usually refer to HV. You haven’t even noticed what my username means, cause well you don’t know much about HV.
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Lol I was expecting that kind of comment. btw, what matters my guru? if its 2000V? or 2004V? will it make any difference in your VHV circuit? ;D If i'm the one who do your mod... wait for Joe the Que Smith to do the bashing ;) or at least lets wait for his comment on that cheapy uni-t circuit.
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