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| What are - for you - the 3 biggest disadvantages of your benchtop DMM(s)? |
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| bdunham7:
--- Quote from: floobydust on September 03, 2020, 05:22:24 am ---I understand benchtop DMM's are fragile. Cat. II 300V is 2,500V/12R impulse. Will a BBQ lighter kill it? --- End quote --- They aren't that fragile, at least properly made ones. Your CAT II/300 test requires clamping 100+ amps, the BBQ lighter is just a bit of ESD. The two are not similar events in any way. --- Quote ---"Keithley products are designed for use with electrical signals that are measurement, control, and data I/O connections, with low transient overvoltages, and must not be directly connected to mains voltage or to voltage sources with high transient overvoltages. Measurement Category II (as referenced in IEC 60664) connections require protection for high transient overvoltages often associated with local AC mains connections. Certain Keithley measuring instruments may be connected to mains. These instruments will be marked as category II or higher." --- End quote --- That's a lot of words to simply say you need a CAT II rating to measure non-isolated mains-derived sources. Keithley DMMs will all meet at least CAT II AFAIK, but there are scanner cards and so on that do not. |
| mansaxel:
--- Quote from: tautech on September 02, 2020, 10:06:27 pm --- Obtaining the equipment to verify its performance will cost more than replacing it. --- End quote --- Makes perfect sense. I'd totally do that. Because I would learn something! And, GAS. |
| bson:
I wouldn't pay extra for any cat ratings whatsoever, for a bench instrument whose purpose is things like measuring the linearity of a high resolution DAC or ADC. A dog rating however, that I'd pay for! :-DD |
| floobydust:
--- Quote from: bdunham7 on September 03, 2020, 01:48:35 pm ---They aren't that fragile, at least properly made ones. Your CAT II/300 test requires clamping 100+ amps, the BBQ lighter is just a bit of ESD. The two are not similar events in any way. --- End quote --- It's that I want hard proof this very expensive DMM is impulse-tested for differential and common-mode transients to some value say at least 1,500V. Not someone's "opinion", not "designed to" (engineers with good intentions) or "meets" (who says?) or "CE" sticker or "spec'd to" etc. An ongoing problem with multimeters is fake or misleading 61010 approvals. "Cat. II" on the front panel means nothing - was it evaluated to 61010-1, 61010-2-033 ? And even then, a certification agency can make mistakes. Remember the Keysight 600V fiasco it was just terrible. For a bench DMM it's not safety approvals so much as a guarantee it can take a BBQ lighter so I'm not looking at a massive repair cost due to normal use. i.e. DMM6500 has Intertek approval ETL marking for 61010 but Keithley 2000, 2001, 2002 has nothing- which is probably why they frequently get damaged. |
| joeqsmith:
--- Quote from: floobydust on September 03, 2020, 11:35:47 pm --- --- Quote from: bdunham7 on September 03, 2020, 01:48:35 pm ---They aren't that fragile, at least properly made ones. Your CAT II/300 test requires clamping 100+ amps, the BBQ lighter is just a bit of ESD. The two are not similar events in any way. --- End quote --- It's that I want hard proof this very expensive DMM is impulse-tested for differential and common-mode transients to some value say at least 1,500V. Not someone's "opinion", not "designed to" (engineers with good intentions) or "meets" (who says?) or "CE" sticker or "spec'd to" etc. An ongoing problem with multimeters is fake or misleading 61010 approvals. "Cat. II" on the front panel means nothing - was it evaluated to 61010-1, 61010-2-033 ? And even then, a certification agency can make mistakes. Remember the Keysight 600V fiasco it was just terrible. For a bench DMM it's not safety approvals so much as a guarantee it can take a BBQ lighter so I'm not looking at a massive repair cost due to normal use. i.e. DMM6500 has Intertek approval ETL marking for 61010 but Keithley 2000, 2001, 2002 has nothing- which is probably why they frequently get damaged. --- End quote --- 61010-1 is "for electrical equipment for measurement, control, and laboratory use –" -2-033 is for "Particular requirements for hand-held multimeters and other hand-held meters, for domestic and professional use, capable of measuring mains voltage" "It's that I want hard proof ..." I doubt you would ever find it. BBQ starters will very a LOT. I have characterized the one I use, presented the data for it and have shown how it compares with IEC waveform. I would expect completely different results if I went to the hardware store and bought a new one. BBQ starters are going to output several KV, far beyond the 1.5KV you mention. Their rise times can be well under 1ns and pulse width is going to be <100ns. I think the one I used can put out close to 5A peak, far from what the standards call for. If say you pick some magic number (1.5K) as your criteria. Let's not focus on how you came up with it but assume you know this is what you require. What does the waveform look like? What's the voltage rise time into and open circuit? What's it's decay look like? What's the current look like into a short? .... These are the questions I was pondering when trying to come up with a way to benchmark handheld meter. Being unable to locate any sort of existing standards, my proposal was to somewhat follow the surge open circuit voltage waveform, greatly limit the energy available and not superimpose it onto the line. If I applied this type of waveform at 8KV peak to your favorite bench meter and it survived, it may give you a great feeling of comfort but it will not mean you can connect the same meter to 2KVDC or a MOT. Hard proof requires hard requirements. From there it's possible you could have these tests performed at some outside lab. The cost may far exceed the cost of the meter but you would have your hard proof. A beginner may suggest if a meter survives +/-1.5KV DC, it would handle every transient up to that. At one time I made an attempt to provide some insight on how to harden a cheap UNI-T UT-61E and show how a fast edge can be a problem. Sadly, most of the people who watched the video didn't seem to care about the approach to solving this sort of problem. The wiki experts just need to know how to mod their cheap meters. I just finished the chapter on colleges. An excellent book. https://www.amazon.com/Death-Expertise-Campaign-Established-Knowledge/dp/0190469412 |
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