Decent benchtop multimeter for beginner?

[EEVblog]

Multimeters are "calibrated references" in their own right.

If they're calibrated. 😉

Don't confuse "calibration" with a good stable reference. The best reference is one that doesn't drift. It's better to have a reference that is out by say 0.1% and doesn't drift than an expensive "calibrated" reference that might have measured bang on when it was "calibrated", but then drifts over the next year.

[KungFuJosh]

Don't confuse "calibration" with a good stable reference. The best reference is one that doesn't drift. It's better to have a reference that is out by say 0.1% and doesn't drift than an expensive "calibrated" reference that might have measured bang on when it was "calibrated", but then drifts over the next year.

Of course not. But you can have your good stable reference calibrated. If you have 5 meters, it costs much less to have 1 reference calibrated and see how well your meters agree with that.

[EEVblog]

Of course not. But you can have your good stable reference calibrated. If you have 5 meters, it costs much less to have 1 reference calibrated and see how well your meters agree with that.

That "good stable reference" can be your multimeter. After all, it literally contains a stable reference chip.

[KungFuJosh]

That "good stable reference" can be your multimeter. After all, it literally contains a stable reference chip.

Agreed. But in context of the conversation:

I'm more of a "I have two or three decent meters and they all agree to within a digit" sort of a guy.

This is something that calibration doesn't provide, per se.

If you don't want to calibrate your meters, then calibrate something that all your meters can benefit from. Or don't care, because it doesn't matter for most hobbyists. 😉

[Fungus]

Fungus, how do you think you were able to obtain three completely DMMs that agree with each other???  Calibration...

Adjustment.

[J-R]

Fungus, how do you think you were able to obtain three completely DMMs that agree with each other???  Calibration...

Adjustment.

So you adjusted all three so they match, got it.

[tszaboo]

I'm still unclear how "calibration" provides a guarantee unless it's done before and after each critical measurement.

Technically, it doesn't.
That's what "tracability" and "measurement confidence" are all about.

Exactly this. Some time ago we had tthis calibrated shunt for 50A that was used as a transfer standard for calibrating the equipment we were selling. The shunt failed one calibration a year. We checked the relevant standard and the procedure is that you have to recall every equipment calibrated with it since the last passed calibration.

[Phil1977]

I would like to see the person who has a private project going on where his resolution is really necessary.
There are probably not many people who own a 6 digit or more instrument.
At work, we sometimes have projects that require voltage adjustment to 1mV, which is very precise.
Anyone can work out what resolution is sufficient for us.
As a MIL, AERO and ISO certified company, we do not have a 6.5 digit instrument in our inventory.
If you buy something like this privately, 90% of the time it will go to the dog.
Or according to the dog question.
Why does he lick his balls?
Because he can.

Very well said 

My question was not about hobbyists. Hobbies can be crazy, I´d even say they must be crazy. No further details needed.

But professionally - where do you need it?

I professionally often work with photometry. In that field, even the best equipped quality departments with 2m-Ulbricht-Spheres and dedicated black painted 25m long halls for goniometers struggle to get stability of better than 1% for some kind of light sources. In most datasheets of internationally leading suppliers the equipment specified for the performance measurement is required to be of 5% or 10% tolerance.

Anyhow measurements are done. You carefully track standards and multiple golden samples of the product type you are analysing. You sometimes use different standards that are routinely swapped between locations.

If you want to have an accuracy better than 5% then you usually can't buy a better instrument, you have to care for the accuracy by doing lots of comparisons and doing the math.

I perfectly get the point that in electronic metrology many things get much easier if you have a 7.5 digit DMM that always can be trusted for 4 digits relevant for your measurement. But where is it needed professionally? I´d just be curious for examples like: Doing ageing tests of batteries - if the ESR starts to fall for 5ppm then this is and indicator for something (This example was fictional - probably it's so much harder to measure the temperature of a battery than it´s ESR)

[EEVblog]

Fungus, how do you think you were able to obtain three completely DMMs that agree with each other???  Calibration...

Adjustment.

Many people think when you send you meter in for "calibration" that they actually adjust it to be spot on, this is untrue, they just check it and give you a report on the values and whether it's within spec or not.
You have to specifically ask for a "calibration adjustment" if you want this.
And "adjustment" is not something that is normally done in any environment that takes calibration seriously. Why? Because you have just reset all of your tracable history and hence "measurement confidence" of this meter.
It sounds silly, as you just adjusted it to "spot on", but if you understand what tracable calibration is this is something you usually don't want. The tracabe history is usually more important than the absolute value.

[EEVblog]

I would like to see the person who has a private project going on where his resolution is really necessary.

Can be as simple as tracing shorts.

[Phil1977]

resolution != accuracy

That high resolution and a basic stability are super valuable is probably undoubted.

[tautech]

Many people think when you send you meter in for "calibration" that they actually adjust it to be spot on, this is untrue, they just check it and give you a report on the values and whether it's within spec or not.
You have to specifically ask for a "calibration adjustment" if you want this.

Yes and yes but why the industry has retained Calibration as general terminology when it is too simply misunderstood and the fault of the industry.

Instead there need be a change of wording used to Performance Verification and Calibration Adjustment, both of which should never be misunderstood as their meanings are very clear.

[Kleinstein]

For using a meter as a voltage reference, there may be more drift in a DMM than just the internal voltage reference. For many meters there is additional ADC gain and possibly extra dividers / amplifiers. So the meters have it a bit more difficult to be as stable as a reference source. The market for stable ref. sources is relatively small though and a good meter may be easier to get than a ref. source. So using a meter as reference point is still a valid option.

Especially for hobby use one does not care that much about the absolute scale. One still wants the meter to be reliable, stable and linear.

For the short tracing one only needs the ability to resolve small voltages, not really the larger number of digits. Still a higher resolution meter may be a way to get that resolution.

[EEVblog]

Many people think when you send you meter in for "calibration" that they actually adjust it to be spot on, this is untrue, they just check it and give you a report on the values and whether it's within spec or not.
You have to specifically ask for a "calibration adjustment" if you want this.

Yes and yes but why the industry has retained Calibration as general terminology when it is too simply misunderstood and the fault of the industry.
Instead there need be a change of wording used to Performance Verification and Calibration Adjustment, both of which should never be misunderstood as their meanings are very clear.

The industry has gotten by just fine as it is.
Most who take it seriously and pay money for proper tracable calibration know what it is and why they do it.

[Furna]

Many people think when you send you meter in for "calibration" that they actually adjust it to be spot on, this is untrue, they just check it and give you a report on the values and whether it's within spec or not.
You have to specifically ask for a "calibration adjustment" if you want this.

Yes and yes but why the industry has retained Calibration as general terminology when it is too simply misunderstood and the fault of the industry.
Instead there need be a change of wording used to Performance Verification and Calibration Adjustment, both of which should never be misunderstood as their meanings are very clear.

The industry has gotten by just fine as it is.
Most who take it seriously and pay money for proper tracable calibration know what it is and why they do it.

If most (as opposed to all) of the people that pay money know what it is .. than it is definitely ambiguous   

[nctnico]

But professionally - where do you need it?

As Kleinstein noted, a quality DMM is easier to get than a good reference. And a DMM is more versatile as it can measure currents and resistances accurately as well. I'm using a Keysight 6.5 digit DMM to measure initial values of voltage references and reference resistors. The parts I'm using have low drift, low tempco but the initial value can vary more than required so they need calibration to increase absolute accuracy. I bought the Keysight DMM specifically for this purpose alone.

[skander36]

For using a meter as a voltage reference, there may be more drift in a DMM than just the internal voltage reference. For many meters there is additional ADC gain and possibly extra dividers / amplifiers. So the meters have it a bit more difficult to be as stable as a reference source.

...

Indeed! For example:



With some DMM's one have to be quick to catch the "opportunuty window" ...

[slavoy]

And this is where Siglent steps in, offering user adjustment through a .csv file while preserving the factory calibration so traceability remains 

[skander36]

And this is where Siglent steps in, offering user adjustment through a .csv file while preserving the factory calibration so traceability remains 

As Kelinstein said this is about stability. whatever calibration you will do, the descent curve will manifest. This measurement was in about 1:45 minutes, and the decay were in progress.

[slavoy]

And this is where Siglent steps in, offering user adjustment through a .csv file while preserving the factory calibration so traceability remains 

As Kelinstein said this is about stability. whatever calibration you will do, the descent curve will manifest. This measurement was in about 1:45 minutes, and the decay were in progress.

I was reffering to Dave's post to be precise.

Fungus, how do you think you were able to obtain three completely DMMs that agree with each other???  Calibration...

Adjustment.

Many people think when you send you meter in for "calibration" that they actually adjust it to be spot on, this is untrue, they just check it and give you a report on the values and whether it's within spec or not.
You have to specifically ask for a "calibration adjustment" if you want this.
And "adjustment" is not something that is normally done in any environment that takes calibration seriously. Why? Because you have just reset all of your tracable history and hence "measurement confidence" of this meter.
It sounds silly, as you just adjusted it to "spot on", but if you understand what tracable calibration is this is something you usually don't want. The tracabe history is usually more important than the absolute value.

[skander36]

I was reffering to Dave's post to be precise.

Then our posts became interlaced in time.
This is why is good to quote the post referred.

[watchmaker]

This was dealt with by navigation centuries ago in the days of mechanical chronometers.  These were at sea for 3 years at a stretch and had to be consistent (and were, as proved by successful trade and naval maneuvers).

FWIW, these were so successful the USN did not retire mech chrons until GPS was perfected in 1989 even though they had first deployed quartz during WWII.  The quartz did not hold up well at sea.  Now of course, the USN would like some back.

All capital ships carried three chronometers.  Use one and it went rogue, SOL.  Use two and one went rogue, you were guessing.  Use three and one went rogue, you knew which one was bad.

These were calibrated and adjusted to Greenwich at the service depot every three years.  In use they were only wound, never adjusted for time.

Each carried a certificate that provided the calibration error determined over 30 days of observation.  The instruments used an escapement that is remarkably stable over 3 to 5 years and did not use oil (especially important in the days when whale oil thickened over time).

The navigator did not care about the "accuracy" of the dial time.  He used the calibration error to calculate the adjusted dial time so he could determine the actual time back in Greenwich.

Application to meters:

The absolute reading is not as important as knowing the deviation from "reality" on a consistent basis.  As in chronometers, consistency is far more important.

For this and statistical reasons, I agree with Dave that if three random DMMs consistently provide readings that agree to whatever precision is "good enough", then it can be assumed they are reliable.  And an aged instrument has likely reached its highest level of stability (chronometers were run for a year to allow the balance spring of the oscillator to age, and the consistency tended to approve over the 50 to 100 years of service).

Like a navigator, someone working in a high liability position needs annual calibration.  If concerned about changes within that period, they can spot check readings with another calibrated instrument.  Again though, the rule of three would seem to apply.

For the amateur, consistency would seem to be the goal and she/he can assume agreement among 3 DMMs means the readings are likely valid.  This is one approach to assessing convergent validity.

The amateur can also check their DMM by going back to basics, using Ohm's law to determine the expected reading.

I never paid more than $125 shipped for my DMMs, most of the time far less.  All agree within a couple counts on the last 2 digits.  My work range is 120 vac and below; so all but my Agilent 1252 are at least 15 years old with the electronics well aged and stable.

For the amateur buying a used instrument, Ohm's law at delivery is your friend.  Of course, a vetted second instrument is also your friend.  And who does not need at least 2 or 3 DMMs?

[BeBuLamar]

I think the OP doesn't want a benchtop for more resolution or accuracy than his handheld DMM. I think he just want the form factor of a benchtop unit.

[coromonadalix]

since OP has not appeared in HIS thread for a while  loll

[skander36]

And he has received in the beginning some good recommendations from Josh, Nico and Dave ...