Decent benchtop multimeter for beginner?

[Aldo22]

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

He showed that he did something with the 3D printer:
https://www.eevblog.com/forum/testgear/decent-benchtop-multimeter-for-beginner/msg5604207/#msg5604207

[coromonadalix]

oh sorry  thks  missed that one

i retract myself

[Kleinstein]

The comparison of the 34465 DMM6500 and SDM3065 is for the stabilization after turn on. Most of this should be a thermal effect and the 3 meters use the same LM399 reference that should have rather low TC. So the drift observed in the graph is mainly from the extra drift components, not the reference.
The TC of meters can scatter quite a bit between units - so with 3 other units of the same meter types the curves can look quite different (though the same time scale).

For precision use one anyway lets the meter warm up before use - so this initial phase is less relevant. There is however also a chance that longer time drift can happen at the same parts involved in thermal drift.

For the more low price range one can not expect that level of stability (at least from a new one).

[skander36]

...
For precision use one anyway lets the meter warm up before use - so this initial phase is less relevant. There is however also a chance that longer time drift can happen at the same parts involved in thermal drift.
....

After 1h:45 min Siglent still drift.  You want to say that it cannot be used for 2 hours ?
Why the others two are so stable?
Siglent is the older (about 5 years) and is the only calibrated and adjusted (last year) by Siglent in Germany. 

[nctnico]

...
For precision use one anyway lets the meter warm up before use - so this initial phase is less relevant. There is however also a chance that longer time drift can happen at the same parts involved in thermal drift.
....

After 1h:45 min Siglent still drift.  You want to say that it cannot be used for 2 hours ?
Why the others two are so stable?

Pedigree. Knowing how to age voltage references and knowing how to build a DMM properly.

[Fungus]

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.

You adjust them so they match a reference, yes.

[Fungus]

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.

You could do it with a new meter if it doesn't agree with your other meters too well when it arrives. 

[Kleinstein]

...
For precision use one anyway lets the meter warm up before use - so this initial phase is less relevant. There is however also a chance that longer time drift can happen at the same parts involved in thermal drift.
....

After 1h:45 min Siglent still drift.  You want to say that it cannot be used for 2 hours ?
Why the others two are so stable?
Siglent is the older (about 5 years) and is the only calibrated and adjusted (last year) by Siglent in Germany.

If you want good accuracy it is standard to wait some time for the temperature to stabilize. The SDM3065 example may be an especially bad unit. The stabilization looks quite slow - maybe a bad or disabled fan ? It's is not the larger magnitude of the drift, but also looks like a longer time constant.

Many of the meter instruction call for some 2 hour warmup before doing critical measuments (e.g. do the calibration). That is not unusual. One can still use the meter before that, just don't expect the specified accuracy. One can not use it for the first minute or so, because many modern meters take quite some time for boot and an initial power on test. For a really serious meter I would even want a good self test to be run after at least some (e.g. 30 min) warmup, so it can be more stringent than right after turn on when things are naturally still drifting. A power on self test can be more tricky and may need to add extra tolerances for a possibly cold meter.

[2N3055]

Can somebody say how long it takes for KS 34401 to stabilise after power on, please?

[bdunham7]

Can somebody say how long it takes for KS 34401 to stabilise after power on, please?

 

Completely stabilize?  Never, unless you hold the ambient temp to better than +/- 1C.  Stabilize to well within specs, assuming 73C ambient and the meter being in that ambient for a while (48-72 hour) prior to power on?  30 minutes or so.  Stabilize to 1-2 counts?  2 to 4 hours.  All assuming a nominal 10V reference and the 10VDC range.  I've never really tried to test one for other functions, but since AC/ohms/current and the higher/lower DC volts all have worse specs I would think that the power on settling would be less signficant.  And this is all assuming you don't move or reorient the 34401A in any way.

Now ask me about the F8846A. 

[skander36]

If you want good accuracy it is standard to wait some time for the temperature to stabilize. The SDM3065 example may be an especially bad unit. The stabilization looks quite slow - maybe a bad or disabled fan ? It's is not the larger magnitude of the drift, but also looks like a longer time constant.

Many of the meter instruction call for some 2 hour warmup before doing critical measuments (e.g. do the calibration). That is not unusual. One can still use the meter before that, just don't expect the specified accuracy. One can not use it for the first minute or so, because many modern meters take quite some time for boot and an initial power on test. For a really serious meter I would even want a good self test to be run after at least some (e.g. 30 min) warmup, so it can be more stringent than right after turn on when things are naturally still drifting. A power on self test can be more tricky and may need to add extra tolerances for a possibly cold meter.

The meter was come back from Siglent, calibrated and validated as good with a calibration certficate from them. You can see that in the beginning the meter agree with the other two. But then it drift from the initial value while the others two dmm's keep reading in the same time/conditions as 3065X. If this is a defect then Siglent has failed verification and calibration, which I'm  really doubt. My point is that 3065X has not the best design for a 6.5 DMM. 
The fan is working well. Sellf test always pass, the meter was never broken or malfunctioned.

[Kleinstein]

The point of the calibration is to have the meter after warm up to meat it's specs, not just after turn on. The calibration instruction usually call for some 2 hours of warm up. If it only meets the specs directly after turn on, in a cold state, that would be fail. The overall change is also quite large - so maybe a rather poor unit or really weak fan / blocked air flow. Chances are this meter would also have a rather large (negative) TC for the 20 V range.

[skander36]

The point of the calibration is to have the meter after warm up to meat it's specs, not just after turn on. The calibration instruction usually call for some 2 hours of warm up. If it only meets the specs directly after turn on, in a cold state, that would be fail. The overall change is also quite large - so maybe a rather poor unit or really weak fan / blocked air flow. Chances are this meter would also have a rather large (negative) TC for the 20 V range.

As I said before the fan is ok.

[BILLPOD]

 

[Martin72]

Pedigree. Knowing how to age voltage references and knowing how to build a DMM properly.

If the device drifts out of its own tolerance, something is defective, quite simply.

[skander36]

Pedigree. Knowing how to age voltage references and knowing how to build a DMM properly.

If the device drifts out of its own tolerance, something is defective, quite simply.

That is correct! But Siglent said that is ok and in tolerance ...  .. who knows?
Anyway my point was to show the difference between this three meters on drifting.
Having this meter as a single precission DMM make any user happy, but when a second meter is coming, the difference became obvious.

[Martin72]

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.

That's exactly how it is.
This is how an accredited (listed) calibration laboratory does it.
Either it passes or it is blocked with a query as to whether it should be adjusted or not.
As a rule, the devices are then sent to the manufacturer, and after re-adjustment they are sent back to the calibration laboratory.
However:

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.

Spot on again.
This is a popular question from auditors to us (me as the person responsible for the test field and to my measuring equipment representative, who is in charge of calibration and maintains the database of our test equipment):
Regular traceable calibration is all well and good, but what do you then do with the logs and, above all, with the results from them?
Do you simply file them away and only react when a calibration has failed?
What does your reaction look like then?
I can say that if a calibration fails, that would be FATAL.
And that's what the auditor is getting at.
If a measuring device passed calibration last year and now it hasn't, that doesn't mean it's OK, so we have it checked by the manufacturer and then calibrated again.
That means :
- What was measured with the device in the last 12 months after the last calibration, which products.
- Since nobody can say whether the device went out of tolerance after day 1 after calibration or only on day 364 before the next calibration, everything that was measured with it must be questioned.
- Are the products measured with it still in the company? You were lucky.
But rather not, they have already been delivered, then recall actions must be started, with the corresponding consequences such as economic and of course “loss of face”.
This must be prevented at all costs.
Therefore, the task is not only to manage the calibration results but also to check exactly where the trend of the measured values is heading.
In order to be able to intervene in good time if the trend turns negative.

[Martin72]

That is correct! But Siglent said that is ok and in tolerance ...  .. who knows?
Anyway my point was to show the difference between this three meters on drifting.
Having this meter as a single precission DMM make any user happy, but when a second meter is coming, the difference became obvious.

You would have to create a long-term graph and see whether the drift actually goes “out”.
If the drift remains within 0.0015%, this may be unpleasant for personal perception, but not a technical flaw.
If 10V are present, the measured value may be between 9.985 and 10.015V, roughly speaking.
If this is the case, then “unfortunately” everything is fine, you get what you bought.
If I remember correctly, the tendency of an SDM3065X is rather constant “downwards”, at least constant and not up/down.
The behavior opens up possibilities to “improve” this.
Or not, because it is within tolerance.
Or buy something that doesn't “annoy” you so much.

[nctnico]

That is correct! But Siglent said that is ok and in tolerance ...  .. who knows?
Anyway my point was to show the difference between this three meters on drifting.
Having this meter as a single precission DMM make any user happy, but when a second meter is coming, the difference became obvious.

You would have to create a long-term graph and see whether the drift actually goes “out”.
If the drift remains within 0.0015%, this may be unpleasant for personal perception, but not a technical flaw.
If 10V are present, the measured value may be between 9.985 and 10.015V, roughly speaking.

You might have a two decimal places wrong here  . 0.0015% = 15ppm. For 10V this means +/-150uV so between 9.99985V and 10.00015V

If you calculate your numbers back to a percentage, you get to 0.15%.

[Martin72]

My mistake, but the intention behind it remains the same.
As long as you're in, you're in.
If you're not, you're not and then it's a mistake that needs to be corrected.

[KungFuJosh]

He needs his starting voltage, and the mean voltages from the other meters to determine that. It isn't 10V exactly on any of the meters.

If the reference is 9.9998 then 9.9998 x 0.9985 = 9.9848. Or 9.9999 source voltage would be 9.9849. Both of those would be within threshold, no?

ETA: I would like to see data via TestController for an extended period of time, like a couple days or more.

[tautech]

He needs his starting voltage, and the mean voltages from the other meters to determine that. It isn't 10V exactly on any of the meters.

If the reference is 9.9998 then 9.9998 x 0.9985 = 9.9848. Or 9.9999 source voltage would be 9.9849. Both of those would be within threshold, no?

ETA: I would like to see data via TestController for an extended period of time, like a couple days or more.

Can you do one Josh ?
TIA

[KungFuJosh]

ETA: I would like to see data via TestController for an extended period of time, like a couple days or more.

Can you do one Josh ?
TIA

My computer and workbench stuff all get shut off at night. I could probably do one for 12 hours or so. I would let the reference and meter warm up first though.

[Kleinstein]

The drift shown for the SDM3055 is for the warm up period. There are usually no specs for this, the accuracy specs are valid only after warm up for 1 or 2 hours. A rather strong drift after turn on is inconvenient, but not a fault per se. There are usually no hard spec limits for this.

Much of the warm up drift is from the meters TC and the temperature rise for the frist 1 or 2 hours after turn on. So the large shift after warm up points to likely a large TC and this may be outside the specs or at least borderline. The observed change is some 50 ppm and with a 5 ppm/K spec this would mean a 10 K temperature rise. This sounds reasonable and it may not need an out of spec TC to reach that level of turn on drift.

[skander36]

The reason for there are 3  DMM's is comparison.
This is the idea. TWO meters are stable from ther beginning and ONE not so stable. Not the precission.
SDM3065X is not defect. Is just inferior as design.



P.S. Reference value is 10.000005