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

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bdunham7:

--- Quote from: Fungus on September 02, 2020, 08:55:49 pm ---Nowhere in CAT documents does it say the the meter should survive.

--- End quote ---

The 8842A isn't actually 'CAT rated' as far as I know, at least neither CAT xx/yyyV or any reference to IEC1010 appears anywhere on it.  I wonder when that started to be a thing--my earliest product that I can lay hands on that has a CAT rating insignia is my old Scopemeter--CAT III/600V.

However, I don't think this was any type of CAT event.  I think it was subjected to a severe overvoltage, not a transient.   I think it is open for discussion as to whether the meter 'survived'.  IMO it did survive--just a little more repair needed than replacing a fuse. 

bdunham7:

--- Quote from: floobydust on September 02, 2020, 07:13:06 pm ---I frequently go near or over 750-1000V,

--- End quote ---

You might want to rethink routinely running near-limit voltage through your very best DMM (if that's the case).  I either use an HV probe or a less valuable meter when I'm testing unknown-ish high voltages.  The only time I'll run 1000V+ into a 6.5 digit precision DMM is something like adjusting a calibrator (which is what I'm doing right now) where I need that last digit or at least the one before it.


--- Quote ---5. RIGHT TO REPAIR
If you damage the front-end, no schematic is available. Keithley has some kindergarten-grade block diagrams but you will never find that leaky JFET or mux.
Very costly at almost 1/2 the price of the instrument to repair it, which is the going rate. I find many bench DMM's are too fragile for real world use, they need to up the front end protection although pA measurement would suffer I guess.

--- End quote ---

The days of being able to repair fried meters are mostly over.  Even the OEMs can't fix a lot of this stuff and practice 'repair by replacement', either the board or the unit.  But I think they are actually protected remarkably well considering their sensitivity.  Try designing a circuit that responds to 10 nanovolts but doesn't complain when you suddenly stuff it with a kilovolt.

tautech:

--- Quote from: bdunham7 on September 02, 2020, 09:27:42 pm ---
--- Quote from: Fungus on September 02, 2020, 08:55:49 pm ---Nowhere in CAT documents does it say the the meter should survive.

--- End quote ---

The 8842A isn't actually 'CAT rated' as far as I know, at least neither CAT xx/yyyV or any reference to IEC1010 appears anywhere on it.  I wonder when that started to be a thing--my earliest product that I can lay hands on that has a CAT rating insignia is my old Scopemeter--CAT III/600V.

However, I don't think this was any type of CAT event.  I think it was subjected to a severe overvoltage, not a transient.   I think it is open for discussion as to whether the meter 'survived'.  IMO it did survive--just a little more repair needed than replacing a fuse.

--- End quote ---
No it didn't survive, it needed to be repaired before further use.
You saved it from going in a dumpster that's all.

bdunham7:

--- Quote from: tautech on September 02, 2020, 09:44:03 pm ---No it didn't survive, it needed to be repaired before further use.
You saved it from going in a dumpster that's all.

--- End quote ---

That is a perspective that has changed since the time that this meter was originally built.  Damaged but repairable is now no different to most than destroyed and unrepairable, so there is no point in designing things to fail in a repairable way.  It wasn't always that way.

tautech:

--- Quote from: bdunham7 on September 02, 2020, 09:52:23 pm ---
--- Quote from: tautech on September 02, 2020, 09:44:03 pm ---No it didn't survive, it needed to be repaired before further use.
You saved it from going in a dumpster that's all.

--- End quote ---

That is a perspective that has changed since the time that this meter was originally built.  Damaged but repairable is now no different to most than destroyed and unrepairable, so there is no point in designing things to fail in a repairable way.  It wasn't always that way.

--- End quote ---
You repaired it to a condition that works for you, congrats and I mean that however for most that rely on a bench meter for trusted best possible accuracy they would bin it.
Obtaining the equipment to verify its performance will cost more than replacing it.

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