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What are - for you - the 3 biggest disadvantages of your benchtop DMM(s)?

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bdunham7:

--- Quote from: HKJ on September 04, 2020, 03:35:02 pm ---The CAT II 300 is nearly universal, only Fluke will handle more.

--- End quote ---

OK, didn't realize that those meters all had specific 500V-pk to ground ratings as I don't have any of them.  But CAT II/300 doesn't imply that--my modest BK Precision 2831E (by TongHui) is CAT II/300 and yet 1kV max to ground.  Of course it is also CAT I/1000V, so I suppose those meters that omit the CAT I/1000 rating really are fragile in that you can't measure 500VDC or 300VAC without being sure of how it might be ground referenced--so even floating or presumed floating above those limits would be off-limits.  That does seem weak tea.

And then there's the Siglent.  Not sure how you can be CAT I/1000 and still have the 500V-pk to ground limitation.  Perhaps someone with knowledge of the CAT standards could clarify?

tautech:

--- Quote from: bdunham7 on September 04, 2020, 04:14:52 pm ---And then there's the Siglent.  Not sure how you can be CAT I/1000 and still have the 500V-pk to ground limitation.  Perhaps someone with knowledge of the CAT standards could clarify?

--- End quote ---
Specifically this is how it's rated:
Measuring Method and other Characteristics
DC Voltage
CMRR 120 dB ( For the 1 KΩ unbalanced resistance in LO lead, max ± 500 VDC )

bdunham7:

--- Quote from: tautech on September 04, 2020, 04:25:12 pm ---Specifically this is how it's rated:
Measuring Method and other Characteristics
DC Voltage
CMRR 120 dB ( For the 1 KΩ unbalanced resistance in LO lead, max ± 500 VDC )

--- End quote ---

I'm not clear on exactly what that means, but does that mean that there is some other non-protection related reason that the 500V-pk limitation is posted?  I suppose you could design a meter that passes CAT x, but then you otherwise greatly limit its maximums for other reasons.  What confuses me is that although I can't find a specific cite, the CAT voltages are V-rms, so 1000VAC => 1.4kV-pk.  Unless the  IEC procedures allow you to specify the the black lead must be ground referenced--no floating or split supplies-- the math doesn't work.

SilverSolder:

The 3 biggest disdvantages of a benchtop DMM are Size, Size, and Size.

But, that is also their advantage...  Large displays that can be read from across the room in some cases, plenty of knobs and buttons brought out on the front panel for convenience, many options for connectors front and rear, including remote control...   Room inside for better / more stable electronics with more features.  They are heavy enough not to slide around on the table in use...



tautech:

--- Quote from: bdunham7 on September 04, 2020, 05:06:06 pm ---
--- Quote from: tautech on September 04, 2020, 04:25:12 pm ---Specifically this is how it's rated:
Measuring Method and other Characteristics
DC Voltage
CMRR 120 dB ( For the 1 KΩ unbalanced resistance in LO lead, max ± 500 VDC )

--- End quote ---

I'm not clear on exactly what that means, but does that mean that there is some other non-protection related reason that the 500V-pk limitation is posted?  I suppose you could design a meter that passes CAT x, but then you otherwise greatly limit its maximums for other reasons.  What confuses me is that although I can't find a specific cite, the CAT voltages are V-rms, so 1000VAC => 1.4kV-pk.  Unless the  IEC procedures allow you to specify the the black lead must be ground referenced--no floating or split supplies, the math doesn't work.

--- End quote ---
I take it to mean the LO (negative) lead has a max +500VDC rating WRT mains ground.
Which implies for HV or floating measurements with a 500+VDC offset relative to mains ground connect the positive (Hi) lead first.
CAT ratings will be in addition to this.

I suspect it's due to internal clearances primarily as a question I sent to Siglent's tech support recently about series ganging their PSU's had the same 500V limitation in that you can series several units together as long as the 500V max was observed.....which is also specified in their PSU datasheets.

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