UNI-T UT61E First Problem...

[janoc]

I wouldn't expect it would be directly across the piezo and the driver to be fairly low voltage.   I assumed it would have a transformer in the head to drive the piezo.   This is why I brought up the grill starter and asked for specific part numbers.    I wouldn't call it a Darwin award by any means.  It's fairly low energy and I would have thought normally not enough to damage a meter.  But again, I have shown the problems with the UT61E when looking at fast edge transients.  Well, and other UNI-T products as well.. 

Well, seriously, that meter being used on a 380V three phase installation would be asking for a Darwin award regardless of whether or not there is only a low voltage on the piezzo. Imagine a ground fault or a high energy mains transient (definitely not unheard of in a factory) on that machine while the sparky is poking around with that Uni-T meter. That's a straight CAT III environment vs a meter with an insufficient input section and fake safety ratings. People have died because of such combination.

That these meters "pop" simply because of ESD is only an icing on the cake ...

[seanspotatobusiness]

Can I use the Uni-T UT61E to measure the output of a laptop CCFL inverter? I'm not sure what the voltage is but it's at least several hundred volts. Could it be over 1000 V? Perhaps I can make a potential divider and measure across that?

[stj]

inverters can be anything from 300 to several thousand volts - and they vary with lamp temperature because they are current-regulated.
i wouldnt go near one with a meter - btw, the probes may load the circuit and mess up the feedback resulting in a shutdown.
also, they run at very high frequency's - so most meters wouldnt show much anyway.
you really need a scope with a x100 or x1000 probe.

if it's not working,
check the fuse, the fets, and compare the transformer windings to a known good one. (lucky they usually come in pairs)

[joeqsmith]

Why do you feel looking across the head is a CAT III environment?   Do you really feel the OP was at risk of death making this measurement from a line transient?  If so, why?

[janoc]

Why do you feel looking across the head is a CAT III environment?   Do you really feel the OP was at risk of death making this measurement from a line transient?  If so, why?

The OP posted the machine this was in is an industrial three phase installation. That is about as CAT III as it gets, IMO. That the head itself is not connected directly to the mains is not really that relevant there - the machine was obviously on, connected to the mains when he was doing the measurement, no? Unless the circuit is transient protected or powered from a low energy transformer limiting the potential exposure, I would rather err on the side of safety.

Also he was unlikely measuring only that head in that machine - I doubt an electrician would carry a good meter for measuring the dangerous stuff and then whip out a second crappy meter for the "safe" parts of the machine.

For the record, I was referring to the table 1 in this document:
http://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf

[joeqsmith]

I'm not disagreeing with you but am interested in when you feel you need to treat it as a CAT III environment and if you felt the OP was at risk of death from attaching the meter across the head like they mentioned.  If you really feel the potential hazard is at this level, I am curious do you treat all low voltage equipment (PLCs and such) as CAT III if they are part of a hard wired 3P system? 

Not being there, I really have no idea what else they were probing beyond what they claimed.  I doubt that it was just the head as well but I don't know. 
I don't know how the system is wired inside or whats upstream. 

[janoc]

I'm not disagreeing with you but am interested in when you feel you need to treat it as a CAT III environment and if you felt the OP was at risk of death from attaching the meter across the head like they mentioned.  If you really feel the potential hazard is at this level, I am curious do you treat all low voltage equipment (PLCs and such) as CAT III if they are part of a hard wired 3P system? 

Not being there, I really have no idea what else they were probing beyond what they claimed.  I doubt that it was just the head as well but I don't know. 
I don't know how the system is wired inside or whats upstream.

I was more thinking about doing the measurements on that machine in general with that type of meter as asking for the Darwin award, not specifically about the ultrasonic horn. At least until SeanB mentioned that it could have up to 10kV on it (which the meter certainly won't handle gracefully) with the possibility of high peak currents (so probably some significant energy could happen there).

Re handling the PLCs and similar - that actually depends. If the PLCs are behind a well protected low voltage power supply in a separate cabinet, then that would likely qualify as CAT I (at least according to that Fluke's document).

However, it is fairly common to see cabinets that have both mains and 24V in them (e.g. the power supplies, breakers and the PLCs are in same cabinet). There I would rather err on the side of safety and use a proper CAT III rated meter (and gear) if I am working on it live. It is not that difficult to have a brain fart and stick a probe in the wrong place or have a transient from a motor turning on or off nearby come down the mains cable while I am checking whether the PLC has power.

[joeqsmith]

In general, I would not use this particular on anything sitting on the factory floor.   

So you don't feel that just because the equipment is in a large industrial environment and runs on 3P, that it is CAT III in all cases.    I was guessing the inverter that drives the head are in a separate enclosure as well and it's output is isolated from the mains with SP going to the head.    I've never worked with one.   

http://przyrbwn.icm.edu.pl/APP/PDF/124/a124z3p20.pdf

 

[janoc]

In general, I would not use this particular on anything sitting on the factory floor.   

So you don't feel that just because the equipment is in a large industrial environment and runs on 3P, that it is CAT III in all cases.    I was guessing the inverter that drives the head are in a separate enclosure as well and it's output is isolated from the mains with SP going to the head.    I've never worked with one.   

http://przyrbwn.icm.edu.pl/APP/PDF/124/a124z3p20.pdf

 

Well, three phase fixed equipment (e.g. elevator motors) or industrial equipment is considered CAT III by default. CAT II is only single phase and usually something plugged into an outlet, not a fixed install. I wouldn't say that everything on a factory floor is always CAT III (maybe some real world industrial sparky can shed some light on this?) but if the gear is on a fixed mains connection, I would assume the worst.

I haven't seen these ultrasonic welders before neither, but that schematics showing the driver switches 400V DC on the primary side at fairly decent currents is enough for me to have a healthy respect for something like that.

[joeqsmith]

Well, three phase fixed equipment (e.g. elevator motors) or industrial equipment is considered CAT III by default. CAT II is only single phase and usually something plugged into an outlet, not a fixed install. I wouldn't say that everything on a factory floor is always CAT III (maybe some real world industrial sparky can shed some light on this?) but if the gear is on a fixed mains connection, I would assume the worst.

I haven't seen these ultrasonic welders before neither, but that schematics showing the driver switches 400V DC on the primary side at fairly decent currents is enough for me to have a healthy respect for something like that.

I've seen a fair amount of 1P equipment hard wired as well.    I wouldn't go poking in that inverter with this meter still output is only 500V RMS max in this example and is isolated.  I'm surprised it damaged the UT61E. 

[janoc]

I wouldn't go poking in that inverter with this meter still output is only 500V RMS max in this example and is isolated.  I'm surprised it damaged the UT61E.

It is a resonant converter - if the load is not present/damaged, there could be high voltages present. And he measured essentially across the output transformer, so whether or not it is isolated doesn't play a role.

[stj]

why does every damned post about a UNI-T get hijacked by the people obsessed with CAT ratings who dont even understand that they are to protect the user and not the meter!!!!

example,
the meter is rated for max 600v, and CATx 1000v
if you put 1000v into it and it dies quietly without bursting open in your hand then where's the problem???

[janoc]

why does every damned post about a UNI-T get hijacked by the people obsessed with CAT ratings who dont even understand that they are to protect the user and not the meter!!!!

example,
the meter is rated for max 600v, and CATx 1000v
if you put 1000v into it and it dies quietly without bursting open in your hand then where's the problem???

The problem is that that 600V rating on that meter is absolute BS and that meter shouldn't have been anywhere near that machine in the first place.

The second problem is that if that meter's ratings weren't fake, it likely wouldn't have broken neither because the test voltages during the CAT testing are about in that same ballpark. If the meter has arced through, like shown in the picture posted by the OP, during the CAT testing,it would have likely been a test failure too (arcing is a reason for a test failure, as is insulation breakdown, even if the meter doesn't blow up or still works). You obviously didn't bother to read the entire thread since you have missed that part.

But thanks for randomly jumping in, not reading but feeling the need to educate us about not understanding what the ratings are for! 

[stj]

i did read the thread, and i know you have absolutly no idea what voltage or waveform hit the meter.

[Fungus]

why does every damned post about a UNI-T get hijacked by the people obsessed with CAT ratings who dont even understand that they are to protect the user and not the meter!!!!

example,
the meter is rated for max 600v, and CATx 1000v
if you put 1000v into it and it dies quietly without bursting open in your hand then where's the problem???

Maybe you watch the thread where they leap around as the copper inside vaporizes and turns to gas (ie. "explosion") at voltages/energies well within the CAT levels.

[shteii01]

Because it has 250V glass fuses?

why does every damned post about a UNI-T get hijacked by the people obsessed with CAT ratings who dont even understand that they are to protect the user and not the meter!!!!

[Fungus]

Because it has 250V glass fuses?

Because they have a lot of blank spaces on the PCB where the safety components are supposed to be?

(and as a result: Because they die if you look at them the wrong way?)

But hey, they say "22000" on the front so that makes them a good meter, right?

[joeqsmith]

I wouldn't go poking in that inverter with this meter still output is only 500V RMS max in this example and is isolated.  I'm surprised it damaged the UT61E.

It is a resonant converter - if the load is not present/damaged, there could be high voltages present. And he measured essentially across the output transformer, so whether or not it is isolated doesn't play a role.

So you don't feel the output transformer will limit the power available to the meter?    To be clear,  I am still trying to understand your Darwin comment and if you feel that there was a high risk that an arc flash could happen looking across the head or if you just feel there was enough energy available at head that could have cause the meter to explode and kill the user?     

Also, when you mention high voltages could be present what are you thinking?  10s of KV?  Sub KV?   Again, I test all the meters to just under 1KV, which included a few of the 61's.   But we also know that to get the BW on the 61E, the way the circuit is designed, fast edge transients will pass right on through.   I demonstrated this.  This is why again that I brought up my piezo tests as the head is a piezo.  The edge rates for ESD are sub ns.   It's also why I mention the EMC vs the safety standards.  There may not be a lot of energy but it's more than enough to damage many UNI-Ts I have looked at.    Their circuit board has very little damage from their picture.  What ever waveform damaged it, there was not a lot of energy.   Had the meter been a GS certified version of the 61E, I have my doubts it would have survived as I don't believe they are certified for EMC.

[stj]

Because it has 250V glass fuses?

why does every damned post about a UNI-T get hijacked by the people obsessed with CAT ratings who dont even understand that they are to protect the user and not the meter!!!!

fuses are for current, not voltage range.

[Damianos]

This instrument is specified for voltage measurements up to 10kHz and it used on an ultrasonic device!
What does anyone expect from any instrument when used outside of its specifications?
In the manuals of more expensive instruments there is more information about this, such as a derating factor or also a diagram showing the maximum voltage relative to frequency.
Even if it had been used on a CAT-I device, the result would be similar ...

[stj]

love your Avatar!! 

[janoc]

I wouldn't go poking in that inverter with this meter still output is only 500V RMS max in this example and is isolated.  I'm surprised it damaged the UT61E.

It is a resonant converter - if the load is not present/damaged, there could be high voltages present. And he measured essentially across the output transformer, so whether or not it is isolated doesn't play a role.

So you don't feel the output transformer will limit the power available to the meter?    To be clear,  I am still trying to understand your Darwin comment and if you feel that there was a high risk that an arc flash could happen looking across the head or if you just feel there was enough energy available at head that could have cause the meter to explode and kill the user?     

AFAIK, that hardware was something in the 500W ballpark. So even if the transformer does limit the current, there will still be plenty of energy around for one mighty bang. But my primary concern was not so much the ultrasonic head itself but that the OP was poking around a three phase industrial installation with this meter. A high energy environment with a good possibility of high voltage transients.

Also, when you mention high voltages could be present what are you thinking?  10s of KV?  Sub KV?   Again, I test all the meters to just under 1KV, which included a few of the 61's.   But we also know that to get the BW on the 61E, the way the circuit is designed, fast edge transients will pass right on through.   I demonstrated this.  This is why again that I brought up my piezo tests as the head is a piezo.  The edge rates for ESD are sub ns.   It's also why I mention the EMC vs the safety standards.  There may not be a lot of energy but it's more than enough to damage many UNI-Ts I have looked at.    Their circuit board has very little damage from their picture.  What ever waveform damaged it, there was not a lot of energy.   Had the meter been a GS certified version of the 61E, I have my doubts it would have survived as I don't believe they are certified for EMC.

I believe I have replied to this few times already. The CAT testing requires the meter to withstand 4-6kV (depending on which CAT rating is the test for), without arcing or insulation breakdown (i.e. there must not be any current increase beyond the initial capacitance charge up). If the meter has died because of short ESD pulse, as you are suspecting, then don't you think it would have died also when the same voltage has been applied long term during the CAT tests? (and thus failing the test because of arcing/insulation breakdown). I don't know how steep the test waveform edges are, but the only protection device where this could make a difference are the input clamping diodes - if the edge is short enough that the diode doesn't conduct in time. On the other hand, how much energy could a pulse that short that a diode doesn't open deliver? Enough to blacken the range switch? I somehow doubt that - we would see tons of electronics failing due to ESD left and right in that case (lot of electronics has only the clamping diodes as protection).

Also the fact that the horn is a piezzo is actually a red herring - he wasn't measuring the output of a piezoelectric generator (like your lighter!) but an output of some 30-40kHz driver. Those aren't going to have super fast edges. If for nothing else then for EMI reasons.

Of course, this discussion is pretty academical because the original meter obviously hasn't been CAT tested. And the German version that has been doesn't meet those ratings even with the extra protection devices installed.

[janoc]

This instrument is specified for voltage measurements up to 10kHz and it used on an ultrasonic device!
What does anyone expect from any instrument when used outside of its specifications?
In the manuals of more expensive instruments there is more information about this, such as a derating factor or also a diagram showing the maximum voltage relative to frequency.
Even if it had been used on a CAT-I device, the result would be similar ...

Yep, good point too. I am not quite sure what the OP has been attempting to measure there.

[joeqsmith]

AFAIK, that hardware was something in the 500W ballpark. So even if the transformer does limit the current, there will still be plenty of energy around for one mighty bang. But my primary concern was not so much the ultrasonic head itself but that the OP was poking around a three phase industrial installation with this meter. A high energy environment with a good possibility of high voltage transients.

OK, so you feel a 0.5KW 500V AC RMS supply is enough to cause an arc flash, explode the meter and kill the operator.   I really have no idea what it would take myself to have one come apart. 

Also, when you mention high voltages could be present what are you thinking?  10s of KV?  Sub KV?   Again, I test all the meters to just under 1KV, which included a few of the 61's.   But we also know that to get the BW on the 61E, the way the circuit is designed, fast edge transients will pass right on through.   I demonstrated this.  This is why again that I brought up my piezo tests as the head is a piezo.  The edge rates for ESD are sub ns.   It's also why I mention the EMC vs the safety standards.  There may not be a lot of energy but it's more than enough to damage many UNI-Ts I have looked at.    Their circuit board has very little damage from their picture.  What ever waveform damaged it, there was not a lot of energy.   Had the meter been a GS certified version of the 61E, I have my doubts it would have survived as I don't believe they are certified for EMC.

I believe I have replied to this few times already. The CAT testing requires the meter to withstand 4-6kV (depending on which CAT rating is the test for), without arcing or insulation breakdown (i.e. there must not be any current increase beyond the initial capacitance charge up). If the meter has died because of short ESD pulse, as you are suspecting, then don't you think it would have died also when the same voltage has been applied long term during the CAT tests? (and thus failing the test because of arcing/insulation breakdown).

To be clear, I am suspecting a fast edge but not a static discharge but I don't know.   Sure the energy, waveshape, impedance will all come into play.  If you are asking if I think a device could survive ESD and not surge, sure.  Also, I believe the opposite is true.  There is a reason both are tested.   They are also not an end all.  Meaning if you pass every test the IEC standards call out, its not certain the product would survive in the field.

I don't know how steep the test waveform edges are, but the only protection device where this could make a difference are the input clamping diodes - if the edge is short enough that the diode doesn't conduct in time. On the other hand, how much energy could a pulse that short that a diode doesn't open deliver? Enough to blacken the range switch? I somehow doubt that - we would see tons of electronics failing due to ESD left and right in that case (lot of electronics has only the clamping diodes as protection).

Also the fact that the horn is a piezzo is actually a red herring - he wasn't measuring the output of a piezoelectric generator (like your lighter!) but an output of some 30-40kHz driver. Those aren't going to have super fast edges. If for nothing else then for EMI reasons.

Of course, this discussion is pretty academical because the original meter obviously hasn't been CAT tested. And the German version that has been doesn't meet those ratings even with the extra protection devices installed.

Surge is 1.2us rise.  Pretty slow compared to burst.  I am not sure what all the handheld meters needs to do to pass.   It's all on the safety side of things anyway.   I think you are correct that normally you would not be looking at the output of a piezo generator and it is fairly slow.     However, they were working on the unit because their was a problem.  I don't know on a welder like this if the head is active and you have the meter across it, if the circuit to the head opens whats happens.   Would you see a low energy high voltage fast edge event similar to ESD?

I missed your last comment.  The GS certified 61E does not meet what ratings? 

(added more detail)

[SeanB]

Ultrasonic transducers are almost invariably a tuned LC parallel circuit with the driver pumping it to maintain it, the circulating currents are pretty high, along with the voltages. Voltage depends on the loading, and if the transducer is not too healthy, or if there is no loading then the voltages rise up to really high levels. That the edges are slow is not too much of a concern, even 100pF of capacitor will pass appreciable current at 40kHz if the protection is designed to survive a single cycle of voltage, and dissipate the energy over a 10s period between pulses,
and you slam the same energy in there 400 thousand times, something will melt  or simply turn to vapour.

Ultrasonic transducers in industry are generally only a capacitor with high losses, only in echo location do you get the transducer with integrated transformer, as the cables are long, and it is a lot easier to drive a low voltage high current with a transformer to convert impedance at the far end, than to have an ultra low capacitance cable that will be routable easily and survive ultra high voltages as well cheaply. Ultrasonic cleaners to tend to turn transducers into smoke and shrapnel quite easily, I have a few samples of that in cheap cleaners, but the drivers often survive with only blown diode bridges, dead switching transistors and a blown mains fuse. Transducer is just charcoal.