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

[joeqsmith]

I just took apart an old 8842A that apparently was connected to excessive voltage--at least 1500V---with some power to back it up.  The entire front end protection--4 MOVs and 2 fusible resistors--were incinerated.  I removed the burnt parts and subbed in 2 regular 1K resistors (to be repaired properly later, of course) and the meter works properly and is in cal.  No evidence of any external damage, the circuit board is unharmed (but sooty)  and I'm sure nobody died.  I'd say that is 'robust' although I can't quantify that.

As I have said, the first DMM I ever owned was a brand new Fluke 8000A bench meter.  Fairly costly and on par with what you may find free at Harbor Freight.   This meter has little to protect the sensitive custom ICs.  A simple mistake and you're changing $70 or so (back then) for new ICs and a handful of precision matched passive parts.   Could it be repaired? Sure, I repaired it more than once.   But the downtime and cost drove me to retire the Fluke and move to HP3468A.   An old story.   

While I would guess every meter I have evaluated could have been repaired, given enough time and money,  once the main controller is damaged I scrap them.   In very rare cases, I have gone so far as to replace ICs to recover them.   Only the 121GW prototype, Summit/TPI 194II, Yokogawa TY720, and UNI-T UT181A all fell into this category.   

There have been some really low end meters, like the UNI-T UT90A that have such poor clearances, they sustain a lot of damage but I don't test with enough energy to finish them off.   Not that I am suggesting these are robust meters but they have been repairable.   The UT90A may be the best example of that.   

Without looking at the data, I would guess somewhere around 60% of the meters were scrapped.  I am not suggesting that these products wouldn't be a fine choice for some people.  I'm not here to push any brands or sell meters.  However, personally, I don't have a use for a meter that is damaged as easily as my first Fluke.  The transients I would encounter in my early days are not representative of what I experiment with now days.    For me, the more punishment the meter can take on the bench without downtime, the better.  It's not about safety for me but uptime.   

I've had a few people comment on my degrading the MOVs over time.   After a member here also made the same suggestion, I ran a long term high voltage test on my Fluke 87V where I applied 1.6KV DC.   This meter certainly fulfills my needs for a robust meter but its lacking in other ways.   

Today, I use the 34401A if I need that performance or am running some experiment that I have automated or want to log the data.   After discovering the BM869s and the Fluke 189, if I am working on anything that I have any concerns about HP, I use these handheld meters as I have no doubt that they would survive levels that the old HP would not.



***
SP

[floobydust]

Agilent 34461a
3. Kill me with zeros
000.0005  the leading zeros are bad practice and contain no information.

The leading zeros are likely on purpose to indicate the range.

My rant about it here.


34461a manual has Cat. II 300V rating, Input protection: 1,000 V on all ranges.
The common-mode vs differential-mode voltage limits are not spelled out, for the in-guard isolation barrier. I frequently go near or over 750-1000V, which leads me to my next disadvantage:

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.

[Fungus]

I just took apart an old 8842A that apparently was connected to excessive voltage--at least 1500V---with some power to back it up.  The entire front end protection--4 MOVs and 2 fusible resistors--were incinerated.  I removed the burnt parts and subbed in 2 regular 1K resistors (to be repaired properly later, of course) and the meter works properly and is in cal.  No evidence of any external damage, the circuit board is unharmed (but sooty)  and I'm sure nobody died.  I'd say that is 'robust' although I can't quantify that.

Nowhere in CAT documents does it say the the meter should survive.

[Fungus]

How about this:

https://www.aliexpress.com/item/4000343031770.html

[PushUp]

As a "little" interruption, I want to thank all of you, who shared their personal knowlege and experience so far, when dealing with their equipment at home or at work!!! 

In addition to this, it is always good, to discuss certain aspects in a forum - please go on with it, as this is always helpful and mostly purposeful! It is clear that experts discuss on another level than beginners and this is good, as it helps others to improve!

As a consequence of this (or nevertheless), I want to encourage all users of all level to share their thoughts, as only this creates an overall picture. You cannot post something pointless, as the question "What are - for you - the 3 biggest disadvantages of your benchtop DMM(s)?", is that I wanted to hear your personal opinion, which of course should be different to others, depending on the field you are working on and how experienced you are and your know-how in general.

It is clear, that anybody has different preferences depending on the area of responsibility, which makes it so valuable to share, so that anyone can filter for his/her own needs.


Thank you very much!!! 


...don't want to disturb the flow - over and out... 

[bdunham7]

Nowhere in CAT documents does it say the the meter should survive.

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]

I frequently go near or over 750-1000V,

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.

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.

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]

Nowhere in CAT documents does it say the the meter should survive.

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.

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]

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

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]

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

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.

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.

[ferdieCX]

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.

Not for me. For this reason I didn't bought a benchtop DMM and got a Fluke 87V instead. It is cheaper, more robust, and 4 1/2 digits are enough for me

[bdunham7]

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.

Calibrating it would be part of a proper repair and I will certainly do a complete check at some point.  I understand that the 'average user' doesn't have the means to check the performance, but my point is that in its day, this product would be sent in for service and calibration, not binned.  New stuff, well that does get binned.  But as far as trusting it, at least on the DCV ranges that I've checked so far, it is still more accurate toasted than any product your company sells brand new, so there's that. 

[ResistorRob]

I just have a hobby level bench meter, but it's very accurate, looks great, and and has everything I need at a great price.
However, it's missing just one feature that I wish it had....

- Data Logging!

If it had that I might cross the Keithley off my lust/dream meter wishlist :-)
(ok, probably not, lol)

[joeqsmith]

I just took apart an old 8842A that apparently was connected to excessive voltage--at least 1500V---with some power to back it up.  The entire front end protection--4 MOVs and 2 fusible resistors--were incinerated.  I removed the burnt parts and subbed in 2 regular 1K resistors (to be repaired properly later, of course) and the meter works properly and is in cal.  No evidence of any external damage, the circuit board is unharmed (but sooty)  and I'm sure nobody died.  I'd say that is 'robust' although I can't quantify that.

Nowhere in CAT documents does it say the the meter should survive.

Again, 61010-2-033 section 14.101 states:  "The component shall not rupture and shall operate as intended during the test."   

IMO, operate as intended means just that, the DMM continues to read properly. 

One of the tests I have shown several times is from section 101.3.2.   The criteria, "During and after the test, no damage to the equipment shall occur."  IMO, that's not the test equipment being used to test the DMM they are referring to, it's the DMM.

"After the voltage of 4.4.2.101 has been applied to the METER, the METER shall continue to be
able to indicate the presence of HAZARDOUS LIVE voltages up to the maximum RATED voltage.
NOTE The METER is not required to maintain its normal accuracy. A maximum deviation of 10 % is acceptable."

Of course there are many other cases as I have mentioned before.  But again, just to be clear, this is outside of my area and I am providing my interpretation of what the standard states.    I would find it hard to believe for example that the pass fail criteria for an impulse test would be if the combo generator was damaged or not.    Fungus may see it otherwise.   

That said, I would imagine that some of the meters I have looked at would pass both the safety and EMC standards with a wide margin but there are far more that wouldn't come close.   

[zitoune]

I have the Keysight 34461A, and for me the booting time is a disadvantage compared to any handheld DMM.

You cannot do a quick measure on the spot, so most of the time I keep it running for long periods without necessarily using it.

[joeqsmith]

Nowhere in CAT documents does it say the the meter should survive.

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.

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

We may think of a loved one who lived through all the treatments of cancer as surviving.  However, I don't see it this way when it comes to test equipment.  If it was exposed to an event that required repairs, it didn't survive.  Rather I would say it was repairable or salvaged. 

[wizard69]

I just took apart an old 8842A that apparently was connected to excessive voltage--at least 1500V---with some power to back it up.  The entire front end protection--4 MOVs and 2 fusible resistors--were incinerated.  I removed the burnt parts and subbed in 2 regular 1K resistors (to be repaired properly later, of course) and the meter works properly and is in cal.  No evidence of any external damage, the circuit board is unharmed (but sooty)  and I'm sure nobody died.  I'd say that is 'robust' although I can't quantify that.

Nowhere in CAT documents does it say the the meter should survive.

CAT is about keeping the user safe.   The meter may not be functional but it shouldn't harm the user when an accident happens.

[bdunham7]

If it was exposed to an event that required repairs, it didn't survive.  Rather I would say it was repairable or salvaged.

OK, fair enough.  I did say it was a debatable point.  Would you say the same for a meter that required the replacement of an internal fuse after exposure to excess current?  If not, then why would you have a different opinion when the items that 'failed' (actually they worked) are protective devices specifically intended for this purpose?  Of course, I'll grant that the MOVs might not fall into the same category as the fusible resistors, incineration isn't their normal mode of operation. 

My gripe here isn't about the definition of 'survived', it is that the aversion to repairability is causing people to completely shun 'repairable' failure modes.  Why have MOV protection when they could fail?  Just let the CPU take the hit--after all dead is dead.  I suppose that's true for cheap consumer products and things we send into space, but I don't think it should be for expensive instruments--at least where it is practical to build them otherwise.

[tautech]

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.

Calibrating it would be part of a proper repair and I will certainly do a complete check at some point.  I understand that the 'average user' doesn't have the means to check the performance, but my point is that in its day, this product would be sent in for service and calibration, not binned.  New stuff, well that does get binned.  But as far as trusting it, at least on the DCV ranges that I've checked so far, it is still more accurate toasted than any product your company sells brand new, so there's that. 

Yes well I could tell you a horror story of a mate that recently bought a spanking new DMM6500 but I shouldn't. 

Let's just say it got sent back to the US to get sorted and arrived back here in NZ still not right. 

[joeqsmith]

If it was exposed to an event that required repairs, it didn't survive.  Rather I would say it was repairable or salvaged.

OK, fair enough.  I did say it was a debatable point.  Would you say the same for a meter that required the replacement of an internal fuse after exposure to excess current? If not, then why would you have a different opinion when the items that 'failed' (actually they worked) are protective devices specifically intended for this purpose?  Of course, I'll grant that the MOVs might not fall into the same category as the fusible resistors, incineration isn't their normal mode of operation. 

My gripe here isn't about the definition of 'survived', it is that the aversion to repairability is causing people to completely shun 'repairable' failure modes.  Why have MOV protection when they could fail?  Just let the CPU take the hit--after all dead is dead.  I suppose that's true for cheap consumer products and things we send into space, but I don't think it should be for expensive instruments--at least where it is practical to build them otherwise.

In the case of the fuse, we are talking about a user serviceable component.   Of course, you may consider all component user serviceable but that's not what I am referring to.  The manuals for a meter will commonly detail how to test and replace the fuses, along with providing details about what to replace them with.   In some cases, meters like my HP34401 and Fluke 8000A, the fuse (for the current measurement) can be accessed without opening the case.   The fuse was designed to prevent damage to the user (say an arc flash) as well as protect the meter.  Other parts, like MOVs, surge rated resistors.... are soldered in place.  They are not called out in the manual as something the user should be servicing.   If the only damage was the fuse, then I would say the fuse blew but the meter survived.   Say some idiot uses the wrong fuse or even better, jumps the fuse they blew and then the meter is exposed to something that damages other components, I would say you not only damaged your meter but you were an idiot for not following the manufactures requirements. 

Once the parts are soldered into the board, they become part of a larger assembly and require special skills to service.  Of course this doesn't prevent some people from attempting to do repairs they may not be qualified to do.   Again, as we have seen in many posts, there are people who are not qualified to change a fuse.   As to your comment about repairability,  I imagine in cases where we have unqualified people working on safety equipment, we run into cases where they create an unsafe condition (say the person jumping the HRC fuse).  If something were to happen, I would assume the manufacture will be named on the suit.   We may see a time when fuses are no longer user serviceable. 

As I said, the MOVs, PTC, GDTs, surge rated resistors, high speed clamps that you find are there to try and make the meter more robust so it survives various events the user exposes the DMM to.    If we exceed the limits of what any of these combined parts can handle, we have damaged the meter.    If we can salvage or repair it, comes down to the cost/time.  If these parts save the downstream ICs, then I will typically repair them.  If not, they are normally scrapped.

[Rasterist]

Keysight 34461A:  takes too long to boot up.  Especially annoying since it's never completely off; there's an LED on the front indicating it's only asleep.  Nevertheless, it's 29 seconds from hitting the power button until being able to make a measurement.  For this reason, I always reach for my Fluke 87V unless I need the precision or some other unique feature of the 34461A.

[floobydust]

I frequently go near or over 750-1000V,

You might want to rethink routinely running near-limit voltage through your very best DMM (if that's the case)...

I understand benchtop DMM's are fragile. Cat. II 300V is 2,500V/12R impulse. Will a BBQ lighter kill it? These kinds of small transients (not mains spikes) are commonplace to a multimeter when doing SMPS work for example. You get a fast dV/dt and it's a little hit. I don't want to find out the hard way the benchtop DMM is too fragile for practical use.
I've also made test benches for products using benchtop DMM's and a mux for bed-of-nails automated testing. Sometimes there is a failure (connection, pogo-pin, software etc.) and the DMM gets overloaded. I think it's a reasonable use-case. I see a couple MOV's, couple gas-tubes but no PTC in common benchtop DMM pics. Their relays are like 1,000V or 1,500V isolation. They have weaker front-end protection and questionable transient testing 61010 certificates.

"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."

[0culus]

If it was exposed to an event that required repairs, it didn't survive.  Rather I would say it was repairable or salvaged.

OK, fair enough.  I did say it was a debatable point.  Would you say the same for a meter that required the replacement of an internal fuse after exposure to excess current?  If not, then why would you have a different opinion when the items that 'failed' (actually they worked) are protective devices specifically intended for this purpose?  Of course, I'll grant that the MOVs might not fall into the same category as the fusible resistors, incineration isn't their normal mode of operation. 

My gripe here isn't about the definition of 'survived', it is that the aversion to repairability is causing people to completely shun 'repairable' failure modes.  Why have MOV protection when they could fail?  Just let the CPU take the hit--after all dead is dead.  I suppose that's true for cheap consumer products and things we send into space, but I don't think it should be for expensive instruments--at least where it is practical to build them otherwise.

Lack of repairability is largely pushed by the vendors, and it really started in the 1980s and has only gotten worse. Why? Well, now when you break it out of warranty they can sell you a new one. They all like to maintain their trade secret designs too. 50 years ago this was not the case. Crack open the manual for a Tektronix 500 series oscilloscope...it is plainly obvious that they intended the end user to service their own instrument. They even gave you a roll of silver bearing solder! Then go download a manual for the 24xx series scopes and it's obvious how things had changed even by 1990 or so. 

That doesn't mean new stuff is unrepairable; the company just won't help you out at all. You have to reverse engineer it and understand how it works and the failure mode, and maybe have a few special tools. A perfect example of this is the infamous "red ring of death" failure for Microsoft's Xbox 360 game console. Many of them got thrown away, but it's really a failure of the BGA under the CPU, and it can be easily fixed if you have the capability to reflow. Also "The Signal Path" on youtube; his expert knowledge allows him to repair test gear that would otherwise get tossed.

Personally, I don't do very much work around truly high energy stuff (beyond single phase wall voltage), but if I did I certainly would want NEW equipment and not repaired equipment. It's not worth gambling your life when arc flash hazards are involved. For everything else I play with on my bench, repaired old equipment all the way.

[joeqsmith]

I understand benchtop DMM's are fragile. Cat. II 300V is 2,500V/12R impulse. Will a BBQ lighter kill it? These kinds of small transients (not mains spikes) are commonplace to a multimeter when doing SMPS work for example. You get a fast dV/dt and it's a little hit. I don't want to find out the hard way the benchtop DMM is too fragile for practical use.

I never thought I would see the small lighter I use damage any meter but here we are.  Countless UNI-Ts dead and even the holy grail, the 121 was damaged to where it threw off the measurements a fair amount.   It's hard to believe as that ignitor is so weak.   

While I would assume most people would take steps to reduce ESD in their labs, its the other transients that I am also concerned with.  When I was young, I built a power supply like many beginners.   I then proceeded to hook it to all sorts of things.  One was an electromagnet.  I wasn't educated to know what BEMF was.  40 some odd years later, I have MOVs and TVSs internal to all my supplies.     They still are not bullet proof.

Imagine the beginner wanting to measure the resistance change of their large electromagnet.  They attach their meter across the coil, measure the resistance, then power up the coil with their 9V battery, let it heat and then remove the power by disconnecting the leads.  The beginner who swears they never play with HVs has just damaged their new meter.      Most of us do dumb things like this at one time or another.  It's how we learn.   

IMO, cheap meters have their place.  But a beginner who buys a meter that can't survive even that stupid grill starter and other basic transients may find themselves buying another meter.   Steering beginners to buy robust meters that may survive all the thing they expose them to, may make learning electronics more enjoyable but stressing about the meter you just blew up because of some stupid mistake is part of it.   I can't see robbing a beginner of that experience..     

[SilverSolder]

3478A:

1. Horridly bad LCD display
2. No continuity / feeper
3. Terrible front panel legend meaning I always stick my probes in the wrong holes.

That’s about it.

A DYMO labeler could be your new best friend!