When cold, I am expecting with a kV applied, the initial draw is somewhere around 1kV/2000ohms or 500mA. Higher for some of the cheap meters. I doubt many electronics hobbyist have that sort of power supply on hand. I would think the use case was you touch the leads to the live source with the meter set to each function, except for the current. Allowing a minute or so for the PTC to cool between tests. Creeping up on the voltage would seem like a rare case.
As for range switching, I think they do put some thought into that. For example, the Auto Lo-Z function requires you to cross the OFF position to get in or out of it.
The concern would be engaging a low voltage clamp and opening the contact with a kV DC applied. I don't see too many meters surviving that but I've never tried it.
For AC, thing could get interesting if you are suggesting that any frequency is open game. We just need to stay below the printed voltage on the meter. I cooked that UT61E+ doing just that and suspect that may of these cheap meters that only use a PTC to limit the current would be damaged well below their claimed level. I'm not sure how that fits into your criteria.
The concern would be engaging a low voltage clamp and opening the contact with a kV DC applied. I don't see too many meters surviving that but I've never tried it.I think the meter's main defense against that would be that the PTC quickly lowers the current to a level that a switch can maybe handle. If you spin the dial with the power on, you may defeat that feature. I suspect that even if the meter doesn't burn up on the spot, there would be cumulative damage.
Your 116 specs the frequency to 50kHz. Dave's 121GW, 1MHz. Seems like the 121GW should handle 1MHz within the voltage limits. Maybe...
Of course, I would think a meter with a spec'ed freq counter at 220MHz would be able to read 220MHz before the solder starts to reflow and the case melts.
The 20J may be overkill but all you safety experts posting here already know where that number came from.
Hmmm. Is it because that is about the energy used in a defibrillator or because it matches up with the output of an electric fence charger (a powerful one)?QuoteYou may not agree but hopefully you at least now have some understanding why I will continue to call my transients low energy.
Thanks for the detailed explanation. Low is a relative term, of course, and relative to MOV ratings, IEC transients, etc, 20J is obviously much lower. The comment I responded to was talking about damage to semiconductors, etc and there 20J will pop the lid on quite a few devices. I think the low energy events he was referring to are the sorts of noise, ESD or spikes that might get through normal filtering for reasons other than that they overwhelm the protection systems by simply exceeding their voltage or energy limitations. Piezo igniters and 220MHz RF come to mind....
Silly you for believing anything printed on a UNI-T box..... Did you ever figure out what the output voltage and power of that RF amp was?
To melt the solder what, 20W - 40W? A bit of damage to the PCB, 80W? Say the meter presents 5 ohms @ 120MHz, 20V would get you 80W. Just a ballparkish guess. Let's say double that. Does 40V seem like a lot to you? I mean, I thought you were all about kVs?!
There must separate path injecting current into DUT for resistance and capacitance, and this composite 1 MOhm resistor is measurement path for these ranges. There will be transistor clamp after it somewhere before going into DMM chip. ...
Nice job sir. Do you have the tools/skills needed to remove one of the resistors that make up the chain R8-R2?
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And your 8506A, despite being a specialized HF AC instrument, is only good for half that. Having a wirewound resistor or a common-mode toroid right at the front end might help in these extreme cases, but I suspect that level of RF will burn up lots of things. If you're doing it some more, I'll watch from here.
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I actually bought a cheapo hot air gun a couple of weeks ago. Maybe this is the opportunity to take it out of the box.
Consider the newer small Fluke multimeter input protection circuit, instead of desoldering things.
You can see the three main channels, the 1MEG, 10MEG and how they are used.
It seems like you are backing down about surviving the max marked voltage on the face of the meter. Rather we need to actually read the manual and understand the specs to save the meter.
Your 116 specs the frequency to 50kHz. Dave's 121GW, 1MHz. Seems like the 121GW should handle 1MHz within the voltage limits. Maybe... Of course, I would think a meter with a spec'ed freq counter at 220MHz would be able to read 220MHz before the solder starts to reflow and the case melts.The concern would be engaging a low voltage clamp and opening the contact with a kV DC applied. I don't see too many meters surviving that but I've never tried it.I think the meter's main defense against that would be that the PTC quickly lowers the current to a level that a switch can maybe handle. If you spin the dial with the power on, you may defeat that feature. I suspect that even if the meter doesn't burn up on the spot, there would be cumulative damage.
Maybe. It would be easy to setup a simple test without a meter and just see if an arc could be drawn. I would use a 1k resistor in series with the PTC, apply the 1kVDC across it, let the PTC heat up, then open the circuit. It's nothing I have ever tried. I'll make a clip of it.
That's the Fluke 15, 17 family. The 101, 107 only uses two MOV's. Point is it's been optimized beyond the classic 87 input protection, and for cost as well.
And here is an important announcment for The Uni-t Ut60e Protection Circuit Variations Collector Society:
(short: TUUPCVCS)
There is a possibly really unique version aviable in Sweden, the Clas Ohlsson edition. Which is a kind of store chain. Being a swedish version I suppose maybe it comes with REAL fuses from the Nobel factories.
(Note for the Fluke test guys: Reinforce the blast shield if testing those!)
Being a rarity and a collectors item soon, I consider sending it to anyone for a symbolic 2000 Euro price. (Shipping included) It would be a solid investmen in these hectic days! (No I don't have it yet, so can't post pictures.)
Left on for 10 seconds, survives just fine at the nominal 245V here. Readings a smidge low as the PTC recovers.
So I'm curious about why these tests would be conducted at those levels on meters with a CAT-anything label at. Should the meter not withstand, without damage, the application of full rated voltage (1000V in this case) to any input on any setting? AFAIK, even supposedly fragile CAT I bench meters will pass that test. Some older pre-CAT bench meters have separate, lower specifications for voltage protection on ohms and such, but even the old Fluke 8842A will pass that test.
Link to the persons posts who had asked about this may be found here:
https://www.eevblog.com/forum/repair/uni-t-ut61e-diode-mode-repair/
Some of the smaller PTCs are only rated for 500V. Some meters have only a single PTC which if the low voltage clamp is active, will have well over 900V across them.... Maybe.... Turn the dial, I suspect you will get a light show.
***QuoteI'm referring to meters that some claim to be properly rated, not ones where there isn't any dispute that the CAT info printed on them is a bad joke.
Sorry, I missed that part. If a KVDC were applied with unlimited current and the function switch were rotated, I suspect you would burn the contacts on most meters. I wouldn't recommend anyone attempt it.
And here is an important announcment for The Uni-t Ut60e Protection Circuit Variations Collector Society:
(short: TUUPCVCS)
There is a possibly really unique version aviable in Sweden, the Clas Ohlsson edition. Which is a kind of store chain. Being a swedish version I suppose maybe it comes with REAL fuses from the Nobel factories.
(Note for the Fluke test guys: Reinforce the blast shield if testing those!)
Being a rarity and a collectors item soon, I consider sending it to anyone for a symbolic 2000 Euro price. (Shipping included) It would be a solid investmen in these hectic days! (No I don't have it yet, so can't post pictures.)I only found a UT61D, not UT61E: https://www.clasohlson.com/se/Multimeter-med-USB-UNI-T-UT61D/p/36-4717
That said your post is funny.
However it seems to be the bog standard "Chinese" version and not the "GS" branded version because the listed spare fuses for it are 1A 240V for the mA range.
But they are 0.5A 600v in the "GS" version.
And the linked manual on their page also claims the instrument is CAT-IV rated at 600v and CAT-III at 1000v which we all know is blatantly false.
(The GS rated meter is CAT-III 300v and CAT-II 600v but even that is a stretch if you follow the link in my quote below from Joe).
From another TÜV 61010 test report, they added tests:
16.2DV.1
"Multifunction meters and similar equipment shall be tested by changing the function /range selector to all possible settings while connected to the maximum rated source."
16.2DV.2
"Compliance is checked by testing to verify no HAZARD occurs when switching selector settings."
Consider the newer small Fluke multimeter input protection circuit, instead of desoldering things.
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Even just a V-Hz number, as if the average user can do math in their head, won't help. I'm pretty sure that almost any meter can take 10mV @ 1GHz, but not many will do well at 1GV @ 10mHz! So yes, that is always going to be an RTFM specification, its just a shame that most manuals omit this entirely, even when the meter has specifications that might invite disaster.
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Even my 8505A would like to stay below 2*107. And your 8506A, despite being a specialized HF AC instrument, is only good for half that. Having a wirewound resistor or a common-mode toroid right at the front end might help in these extreme cases, but I suspect that level of RF will burn up lots of things. If you're doing it some more, I'll watch from here.
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