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| New UNI-T UT892 2000V AC/DC High Voltage Multimeter |
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| Mechatrommer:
and i dont have to show you whats mine to prove anything... you've concluded... --- Quote from: PartialDischarge on September 09, 2022, 03:04:02 am ---...cause well you don’t know much about HV. --- End quote --- thats enough to make you feel happy. for now, i'm looking forward to hear whats mr joe have to say about this... cheers. |
| joeqsmith:
--- Quote from: Mechatrommer on September 09, 2022, 06:27:35 am ---and i dont have to show you whats mine to prove anything... you've concluded... --- Quote from: PartialDischarge on September 09, 2022, 03:04:02 am ---...cause well you don’t know much about HV. --- End quote --- thats enough to make you feel happy. for now, i'm looking forward to hear whats mr joe have to say about this... cheers. --- End quote --- I would have no way of knowing anyone's level of intelligence except from their posts. That could be misleading. --- Quote from: PartialDischarge on August 28, 2022, 07:04:56 pm --- --- Quote from: joeqsmith on August 28, 2022, 06:59:03 pm --- --- Quote from: floobydust on August 28, 2022, 06:50:54 pm ---Who would trust Uni-T for safety or minimal honesty? ... Have to see a teardown and BBQ lighter test lol. --- End quote --- We could get one and treat it as a special case, cause it's a special meter. Maybe just test the 2kV input only. I ran one of their high voltage sticks. It died fairly early on as well. --- End quote --- I’ll do that when it arrives with my Hipotronics HD140 --- End quote --- Assume this was done before mods to meter. I'm still waiting on results. --- 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 --- +/-1V of reading or full scale? What are you using to make these measurements? Are you planning to do any other testing with it? --- Quote from: PartialDischarge on September 08, 2022, 06:52:38 pm --- --- Quote from: Gyro on September 08, 2022, 06:46:50 pm ---It looks as if there would be sufficient space to insert a strip of insulating material down the side of the PCB, retained by the front and rear, to bolster the minimal isolation of the case flange. I think the 2.5M resistors are probably still above their element limiting voltage though. --- End quote --- 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. --- End quote --- If I understand your first post about your modifications, you were concerned about the original 2.5M resistors being unsafe and the reason you made these changes was to improve safety? Your feelings that the accuracy was improved was a side effect? If this is correct, how did you determine that these mods are safer? I would like to see the backside of the PCB if you took any pictures when you made these modifications. |
| PartialDischarge:
The accuracy I did test full scale, although I quickly changed voltages and linearity did seem good, as mentioned I have not had much time. These is done with a Fluke 410B calibrated with a 3458A and Fluke 80E divider. No, the HD140 still have not used on the multimeter since I have it at another place. I don't think the meter is unsafe and the resistors were not changed for that reason. They were changed because not all 1206 resistors are HV and I don't know what the ppm of those resistors are. Plus that PTC is useless and the sooner there is high resistive impedance in a long PCB trace the better, less corona, less prob of "problems". So I'm happier with a 760k resistor up front rather than with a 1.5k PTC. I'll do more tests as time permits, but duty is first! |
| joeqsmith:
Sounds good. Look forward to seeing some additional data from it. |
| floobydust:
You can't tell if the multimeter is safe without doing a spacings analysis. Commonly there is an unexpected arc path- at the rotary switch, to a mounting screw or nearby part etc. We haven't seen the other side of the PC board. Uni-T is doing their usual cheap ass front end - no MOV, no GDT's, no surge resistor. PTC's are way too slow 10's msec to heat up- leaving the tiny SOT-23 clamp diodes. Hello BBQ lighter lol. Look at the PCB and see the option for a larger SOT-89 clamp transistor Q1A instead of Q1+Q2. Thanks for leaving that one out. They are fully capable of making a decent multimeter, they do this for OEM's but not for their brand name. Just stupid. I think MELF resistors are best for their voltage rating (operating and impulse). With 0805/1206 you run into the limitations with the pad spacing, and worse with a zig-zag because the spacing every four resistors is low. The VCR (voltage coefficient of resistance) is surely terrible with cheap parts. I think that would be an issue but there's not a lot of information about that. |
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