Siglent Bench DMMs SDM3065X, SDM3055 and SDM3045X

[Kleinstein]

One reason we selected the KS34465A as our 1st new precision DMM (had an HP & AG 34401A) here at the Labs, was because we hoped/wished/thought or whatever that some of the old 34401A DNA would be in these newer DMMs.

Now we have 3 KS34465As, a pair of 34401As, a DMM6500 and a SDG3065X, and they all agree well altho the SDG3065X is always slightly higher in DCV readings, likely because the LM399 is still "aging".

The KS 34465 has not that much in common with the old 34401, though quite a bit of the 34410. The relevant resistors are more conventional and from what it looks no longer HP custom ones.
The SDM3065 is much different from both in using an integrated ADC chip and this needs extra dividers: one to divide down the 7 V ref. to somerthing like 3.5 V or 5 V and than some divider for the 20 V to get down to the range of the ADC (e.g. 2 V). For this reason the 2 V range is the more accurate with the SDM3065.  Still the 20 V range only got some 5 ppm of extra uncertainty - so they seem to be quite confident in the resistors.

So it is not just the drift of the reference, but also 2 dividers and the ADC chip itself.
The ratio of the 2 V and 20 V ranges would give a hint on at least than one divider stability.

The 34401 has a resistor ratio in the ADC gain and AFAIK this gain is not corrected by some ACAL like procedure. So far the 34401 has a rather good reputation for low long term drift.

[mawyatt]

And now I just became dissatisfied with my SDM3065X    I bought it new from a local distributor, and it turned out the factory calibration certificate was from 2019... I plan to send it for calibration soon and will let you know how it turns out (unfortunately, I don't have a stable reference source to check the drift.)

As mentioned these use an un-aged LM399, this is how Siglent keeps the cost down (select aged LM399s would be expensive, and left to the more expensive KS and Keithley). Might be a good idea to let your DMM run for some time to allow the LM399 to settle some before sending in. We would like to leave ours on all the time, but the fan noise prevents this, so it cycles on and off.

Best,

[slavoy]

Yea I don't worry too much about it. I'll just burn-in it as long as I can, send it for calibration a few times, and I'll have some idea about the overall drift 

[skander36]

My 3065X was sent to calibration after 4 years ...

[Martin72]

And what are the results ?
Passed or not ?

[skander36]

In the calibration certificate it has passed, but you have seen the difference between the KS & KT.
I have send it because it was sligthly out of specs and hoping that it was aged enough after 4 years, to retain calibration, but it seem that it can't.

[KungFuJosh]

In the calibration certificate it has passed, but you have seen the difference between the KS & KT.
I have send it because it was sligthly out of specs and hoping that it was aged enough after 4 years, to retain calibration, but it seem that it can't.

Perhaps the issue is with the lab and not the device? You might want to consider an independent lab for calibration/adjustment.

[Martin72]

@skander36:

Did you get a complete protocol with all measured values or was it again just a siglent-typical one-page explanation sheet ?

[slavoy]

In the calibration certificate it has passed, but you have seen the difference between the KS & KT.
I have send it because it was sligthly out of specs and hoping that it was aged enough after 4 years, to retain calibration, but it seem that it can't.

I have a question because I'm not sure if I'm thinking about the same terms. Was it only calibration, without adjustment? In Poland, the term "calibration" typically does not include adjustment.

[Martin72]

Not only in Poland....
Here, our calibration lab only measure the devices according to their specs - when they´re into them, they have passed.
When not, they will be rejected and we have to decide what to do with it.
On the other hand, the cal lab which calibrate my brymen in 2021, they did readjustements when the meter was out of tolerance.

[skander36]

In the calibration certificate it has passed, but you have seen the difference between the KS & KT.
I have send it because it was sligthly out of specs and hoping that it was aged enough after 4 years, to retain calibration, but it seem that it can't.

Perhaps the issue is with the lab and not the device? You might want to consider an independent lab for calibration/adjustment.

I also thought about that but I'm enough. I cost me 200E plus shipping. I will use KS and KT and will not consider Siglent DMM's for the future.

[Martin72]

Did you get a complete protocol or not ?
If yes, please share the measured DC values with us.
If no, for the money, I would definitely expect and demand a complete protocol from them.

[skander36]

@skander36:

Did you get a complete protocol with all measured values or was it again just a siglent-typical one-page explanation sheet ?

Yes , a complete protocol.
L.E. Some troubles with the forum server, it messed the attachments.

[skander36]

In the calibration certificate it has passed, but you have seen the difference between the KS & KT.
I have send it because it was sligthly out of specs and hoping that it was aged enough after 4 years, to retain calibration, but it seem that it can't.

I have a question because I'm not sure if I'm thinking about the same terms. Was it only calibration, without adjustment? In Poland, the term "calibration" typically does not include adjustment.

I specifically asked for adjustment, not only calibration, but in the protocol pages they do not checked anything. but in delivery note they put a description:
RMA factory calibration including adjustment, ISO calibration.

[Martin72]

Thankyou for sharing.
So everything is inbetween the specs, the meter is OK.
Remarkable:

All measured values are above the respective injected reference value.
In your example, however, the value is below it.
It is hard to imagine that the meter makes a "runaway" downward at 1V, while it is otherwise always above.
When was the last time your voltage reference was calibrated ?

[tautech]

In the calibration certificate it has passed, but you have seen the difference between the KS & KT.
I have send it because it was sligthly out of specs and hoping that it was aged enough after 4 years, to retain calibration, but it seem that it can't.

I have a question because I'm not sure if I'm thinking about the same terms. Was it only calibration, without adjustment? In Poland, the term "calibration" typically does not include adjustment.

I specifically asked for adjustment, not only calibration, but in the protocol pages they do not checked anything. but in delivery note they put a description:
RMA factory calibration including adjustment, ISO calibration.

Info for adjustment wasn't available until recently, first introduced in FW a few years back but an unwieldy process compared to the simple adjustment process that is available to any any user today.

In short, unhappy with any range then provide a precision reference and tweak the value to match.
Yes this the price we pay for not having aged references.

[skander36]

@Martin72
I told you before.
This month is expired calibration so don't need to be calibrated so soon.
Also those values from the table are showed only in the first 2-3 minutes after start. After that it became to decrease slowly.

[tautech]

@Martin72
I told you before.
This month is expired calibration so don't need to be calibrated so soon.
Also those values from the table are showed only in the first 2-3 minutes after start. After that it became to decrease slowly.

Nothing stopping you from making corrections if you have the latest firmware installed.

Defpom shows how:

[skander36]

Nothing stopping you from making corrections if you have the latest firmware installed.

I know, but I didn't succeed using just PDVS2. It is good for checking but not for calibrating a 6,5 digit DMM.
This is why I send it to Siglent.

The ideea of my first post was to show the diference from KT and KS and that will be a good ideea for Martin to think about.

[tautech]

The idea of my first post was to show the difference from KT and KS ..........

Are they fan cooled ?

[skander36]

yes

[Kean]

Thank you Gentlemen, now I´m unsure what to do.

I don't have experience with the Keithley DMM6500 or Siglent SDM3065X, other than reading various good and bad things about them here.

I will note though that I had concerns about buying a second Keysight 34465A after seeing the below linked post a while back, and began thinking about a SDM3055-SC.
https://www.eevblog.com/forum/testgear/keysight-34465a-reliability/msg4104439/#msg4104439

So I haven't bought any of them... but rather invested in a 2nd hand KS 34972A, and more recently a PDVS2mini precision voltage source.

[tautech]

yes

Interesting.
Do KT and KS specify similar warmup times ?

[KungFuJosh]

I will use KS and KT and will not consider Siglent DMM's for the future.

Send me a private message if you want to get rid of that troublesome Siglent DMM. 😉

[Martin72]

and that will be a good ideea for Martin to think about.

Absolutely and thanks again for that.
I was not aware of that at all.
Nevertheless, I am waiting for an offer from Batronix.
And take the following for me:
- The drift comes from the unaged LM399
- The drift itself does not cause the meter to go outside its own tolerance.
- The drift will decrease over time, i.e. when the LM399 has aged "enough" ?
- You should have a high precision voltage reference in your house if you don't want to bring the meter for calibration every year.

Whereas the latter may become obsolete, because:
Such a reference will cost money, not a little money if you want to calibrate a 6.5 digit meter with it.
The reference must then of course be calibrated regularly, which also costs money.
From this point of view, you could calculate how often you can send a meter for calibration, until you have the money out, which you would spend for your own reference and regular calibration.