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

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Fungus:

--- Quote from: bdunham7 on September 04, 2020, 03:59:40 am ---
--- Quote from: Fungus on September 04, 2020, 03:53:32 am ---https://www.aliexpress.com/item/4000343031770.html

--- End quote ---

Did you look at the comparison photos where they are demonstrating it with the probes into a power strip and then connected to a 9V battery.  Perfect for the target market!

--- End quote ---

I don't own one myself but all the threads on it have concluded that it's quite a good meter if you can get past the silly photos and alarm clock part.

Plus you can take it with you on a picnic and listen to music.

floobydust:
Most models have a 500Vpk CM voltage rating and are using slow gas-tubes for protection of that.
If you have a 750VDC source that is earth-grounded, what happens when you first connect one DMM probe? You are trying to fast lift the entire in-guard section (capacitance) to 750VDC.
Compare that with nicely connecting both leads to the (off) HV power supply under test, where the DMM (-) gets 0V potential and upon PSU power-on there is no overload beyond the auto-ranging having gone to the mV range and having to clank relays up-ranging.
A common-mode choke at the input does help against a fast transient - but they don't use those anymore. Very rare to see one, it's extra manual labour. Nowadays, it's tiny smt inductors with low breakdown voltage, 10 miles after the input jacks, pic related.
My position is these multimeters need to have been well tested, that they really withstand ESD and fast transients at their rated voltage because repairs are super expensive.

bdunham7:

--- Quote from: floobydust ---"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.

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"Nothing" is a bit harsh.  Sure, certifications aren't infallible, but what else can you do unless you do your own test?  The Keysight deal was indeed a shitshow and I'm not sure what I would do if I had one of the implicated devices.  A bit more transparency would be reassuring.


--- Quote ---Most models have a 500Vpk CM voltage rating and are using slow gas-tubes for protection of that.

--- End quote ---

Which ones?  I'm not seeing that on mine except on a very old 8505A, which is a reference meter not really intended for bench service use--it has the 500V CM limitation.  Everything else I have is at least 1000VDC/700VAC to ground, and the 8846A has to be at least 1500V common and differential because it allows 1000Vrms inputs--and doesn't go into overload even slightly over that.  I haven't disassembled it to see what it looks like.


--- Quote ---My position is these multimeters need to have been well tested, that they really withstand ESD and fast transients at their rated voltage because repairs are super expensive.

--- End quote ---

I'd prefer repairability, but that ship sailed long ago.

tautech:

--- Quote from: bdunham7 on September 04, 2020, 02:37:43 pm ---I'd prefer repairability, but that ship sailed long ago.

--- End quote ---
Hardly any surprise why in this day and age.

HKJ:
Bench meter voltage on the front:

Keysight 34461A/65A/70A: CAT II 300V, 500Vpk to gnd
Keithley 6500, 7510: CAT II 300V, 500Vpk to gnd
Fluke 8846: CAT II 600V, CAT I 1000V
Rigol 3068: CAT II 300V, CAT I 1000V
Siglent 3045X: CAT II 300V, CAT I 1000V, 500Vpk to gnd
East Tester ET3240: CAT II 300V, 500Vpk to gnd

The "to gnd" is from the black terminal.

The CAT II 300 is nearly universal, only Fluke will handle more.

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