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

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HKJ:

--- Quote from: SilverSolder on September 04, 2020, 05:15:40 pm ---The 3 biggest disdvantages of a benchtop DMM are Size, Size, and Size.

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That depends, if you also have power supplies, arbs, electronic loads, etc. they all stack nicely.

I have 15 devices stacked in a couple of stacks, I would never have had space for them if they had each had their own shape.

Electro Fan:
It's only a matter of time until either the budget or the space is maxed out.

Electro Fan:

--- Quote from: SilverSolder on September 04, 2020, 05:15:40 pm ---
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...

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+1 on advantages...

After years with only handheld DMMs the bench DMM has become the go to DMM.  It takes up more space than the handhelds but it wasn't space I was using, and I never have to look to see where it might be; and it holds still (hands-free) - just grab the leads and measure (although you still have to change out leads based on the connectors needed). 

And without a doubt a large and multifaceted (graphical) display is way better than the relatively small and dim handheld DMM.  Both have their uses - probably should have at least one of each, but unless you have no handheld DMMs it's worth seriously considering a bench DMM.  If you already have a handheld DMM, I don't see any disadvantages in a bench DMM.

joeqsmith:

--- Quote from: bdunham7 on September 04, 2020, 03:55:56 am ---
--- Quote from: joeqsmith on September 04, 2020, 03:11:14 am ---
"It's that I want hard proof ..."
....

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Meters (well made and well specified) typically have a dV/dt limitation of a few million V*Hz, so your BBQ lighter will greatly exceed that, of course. However, I'd consider it poor design if that limitation was anything other than a thermal limitation on whatever absorbs that high frequency energy. 

I'll drag out my old fried 8842A again, here's a picture of the damaged unit with the incinerated parts removed. 

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--- Quote ---Do you see anything in the picture that might help with that fast edge? 
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It's hard to say when it comes to something like ESD.  The edges are very fast and we are dealing with RF.   I addressed the weakness of the UNI-T UT181A by changing the layout.  It should be obvious that even wire will have some inductance and will effect the signal at these speeds.  Surely the large inductor on the front will play into it.   



--- Quote ---Do you think there's room in a hand-held DMM for this type of protection?
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Based on the number of hand-held meters I exposed to not only the BBQ lighter but also my home made gun which produces waveforms more in-line with the IEC standards,  I would say there are certainly ways to design the front ends to survive it. 


--- Quote ---Is there something else that can do the same thing in less space?
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Again, I went into detail the problems with the UT61E and one possible way to solve such a problem.



--- Quote from: floobydust on September 04, 2020, 05:20:58 am ---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.

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We have seen companies like Gossen successfully utilize GDTs in their meter.   I wouldn't suggest that a product that uses them would be any less robust.  The low capacitance and leakage would seem to make them a good fit for higher end products. 

I think my old HP 34401A uses a combination of GDTs, R,C and MOV for the clamp.  The nice thing about this technique over using the GDT alone is that when working with DC, once the transient dissipates and the voltage falls below the MOVs trip point, the circuit resets.   With the tests I run it doesn't really matter as the transients are never superimposed on another waveform.  They always start at 0V and and at  0V, allowing a GDT to clear.     


***
For got to say that your point about the power supply being active and clipping onto it is certainly a valid case and I wouldn't be surprised to hear of meters being damaged this way.   I look at my bench meters pretty much how I look at any other sensitive equipment.  I have learned to treat them with caution.    Now these new handhelds I have started using, not so much.  These things have seen some fair abuse in my hands.

JimKnopf:
In spring I bought a UT 8803e. I was very unhappy with it because it measures very, very inaccurately. In diode mode you can only measure down to 16 Ohm. Below that Err (short circuit) is displayed.

Today my Keithley DMM6500 arrived.
The first tests are very positive. Diode Mode I can measure very accurately down to below 1 Ohm. Continuity test is very fast. The only drawback is that capacitance is only up to 100µF or 20% above (all measurements 20% above max range), i.e. 120µF.

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