New SDS1104X-E missing calibration certificate

[74HC04]

No such claim of ruining calibration is even mentioned in Siglent documentation therefore the intelligent reader will assume there is no risk in running Self Cal which of course there isn't.
To confirm this assumption the factory says:
The user self cal will not destroy the calibration data.

Thanks for pointing this out. I was relucatant to run a self-cal, at least until I've seen a factory calibration certificate, in case I overwote that factory cal. I am seeing a ~1 pixel positive offset especially from CH1 and CH2, which tends to come and go with vertical position, even when the inputs are gnd coupled (is this a "real" ground anyhow?) and regardless of the volts / div setting. Probably just expecting too much from the front-end!  Or is this a rounding artefact, perhaps?

The lack of factory cal certificate in a Siglent tape sealed box worrys me (it's mentioned on the datasheet's packing list and looks as though it should be tucked into the Quick Start Guide), so I will wait to obtain a copy before drawing any conclusions.

[Performa01]

I am seeing a ~1 pixel positive offset especially from CH1 and CH2, which tends to come and go with vertical position, even when the inputs are gnd coupled (is this a "real" ground anyhow?) and regardless of the volts / div setting. Probably just expecting too much from the front-end! 

Isn't this funny? Folks buy a dirt-cheap entry level scope from a Chinese manufacturer and then rant about things that experienced professionals would not expect even from a midrange DSO manufactured by one of the "big boys" and costing more than 10 times as much

Just like the majority of modern DSOs, this one does not have a "real" input ground. So checking anything with input coupling set to GND is completely meaningless.

If you want to check the offset with grounded input, you could use a BNC-Terminator for that (with DC coupling). Or just leave the input open, the difference is really negligible.

If you do so, please check the specifications for offset and gain error in the data sheet (and compare these with even much more expensive instruments) before you start questioning the quality of the (excellent - high sensitivity, low noise) frontend, just because you spot a few pixels deviation somewhere.

Self calibration is there to bring the instrument to the calibrated state. Specifications can only be guaranteed after a self-cal has been performed after at least half an hour warm-up of the instrument. You can bet your bottom dollar that the factory performs such a self-cal before checking the instrument cal state and then issuing the certificate if it's passed. Of course you won't need another self-cal anytime soon unless there were major temperature changes or the firmware has been updated. Yet the temperature in your lab might differ from the one used for the calibration, so a self-cal could improve things.

Self-Cal cannot provide infinite accuracy though. It relies on an internal reference and a highly accurate DAC, but the adjustments don't have infinite resolution. This is true for the offset DAC (for offset calibration) as well as the PGA (for gain calibration). So especially if you look at the trace at high sensitivities (<5 mV, which are just "fake" software zoom in many other even much more expensive DSOs, but are very real in the SDS1000X-E series), the limited resolution of the offset DAC might leave us some visible offset in the realm of a couple 100 µV.

The frontend of a modern DSO has to use an OpAmp for the DC/LF-path of the input buffer. Since it needs to be high impedance, it has to be (MOS)FET. But this means that it cannot be low offset with low TC - and you don't want a chopper stabilized amp in the frontend of a DSO. This is the reason why a DSO frontend cannot be compared to a multimeter, because the latter usually doesn't need a separate OpAmp and even if it did, it would be of the "zero offset" species. It's essentially the drift and temperature stability of this beforementioned OpAmp that causes the offset error (changing with temperature) in a DSO, hence makes the self-cal necessary. The SDS1000X-E can even provide a "quickcal" that kicks in automatically as soon as the instrument detects a condition that might increase the offset error. The gain on the other hand is much more stable anyway.

If you are interested in an exemplary performance verification regarding DC and AC accuracy, you can have a look at the document "SDS1104X-E Review 50-70.pdf" that is attached in reply #1 of this thread:

https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/

In this document, at page 52 you will find a demonstration to measure a DC voltage of 205 V to an accuracy of better than 0.08 %.
Compare this to the specifications and you will learn that this instrument can actually be vastly better than that, especially when it comes to offset accuracy. Still you'll have to live with a small additive error, only visible at high sensitivities.

[Fungus]

Thanks for pointing this out. I was relucatant to run a self-cal, at least until I've seen a factory calibration certificate, in case I overwote that factory cal.

There's nothing to "overwrite", there's really no such thing as a "factory cal" in a device which recalibrates itself at the push of a button.

The certificate only tells you about the numbers they saw on-screen after they pushed that button at the factory under controlled conditions, ie. if it was capable of calibrating itself properly or not.

Your 'scope will give different readings in summer and winter, maybe even in morning/afternoon (depending on the climate control in your workplace). Any readings taken less than 15-minutes after power-on are invalid (try powering it on from cold and watch the DC offset change as it warms up).

Numbers on DSO screens are only approximate, treat them as such. If a reading is really critical then do yet another self-cal just before taking it.

[2N3055]

Thanks for pointing this out. I was relucatant to run a self-cal, at least until I've seen a factory calibration certificate, in case I overwote that factory cal.

There's nothing to "overwrite", there's really no such thing as a "factory cal" in a device which recalibrates itself at the push of a button.

The certificate only tells you about the numbers they saw on-screen after they pushed that button at the factory under controlled conditions, ie. if it was capable of calibrating itself properly or not.

There is absolutely factory adjustments that saves basic correction coefficients into instrument at manufacture time.

Autocal is NOT full adjustment. It only compensates partially for some parameters, and that mainly for thermal drift.
It is more important as a functional verification.
It will compensate some for temperature related drift and make most accurate measurements.

[Fungus]

There is absolutely factory adjustments that saves basic correction coefficients into instrument at manufacture time.

On modern DSOs? Have watch the auto-cal do its thing? You can see it doing binary searches to find the offsets/scales and it they're not tiny adjustments, they can go way off screen.

I know that there are posts here about "lost calibration" on older 'scopes but I doubt modern DSOs need that (it would cost money...)

Let's see...

sds1104X-e lost calibration - zero results
ds1054z lost calibration - zero results

 

[2N3055]

There is absolutely factory adjustments that saves basic correction coefficients into instrument at manufacture time.

On modern DSOs? Have watch the auto-cal do its thing? You can see it doing binary searches to find the offsets/scales and it they're not tiny adjustments, they can go way off screen.

I know that there are posts here about "lost calibration" on older 'scopes but I doubt modern DSOs need that (it would cost money...)

Let's see...

sds1104X-e lost calibration - zero results
ds1054z lost calibration - zero results

 

They go off the screen because full range on A/D is off the screen...
And most of the new scopes don't carry any calibration in battery backed RAM.. And they are new.. Old scopes had time to die in numbers so that statistics is skewed by definition

[Fungus]

They go off the screen because full range on A/D is off the screen...

Obviously.

ie. They have a particular starting point and they have plenty of adjustment built in, no need for "basic correction coefficients".

[74HC04]

I am seeing a ~1 pixel positive offset especially from CH1 and CH2, which tends to come and go with vertical position, even when the inputs are gnd coupled (is this a "real" ground anyhow?) and regardless of the volts / div setting. Probably just expecting too much from the front-end! 

Isn't this funny? Folks buy a dirt-cheap entry level scope from a Chinese manufacturer and then rant about things that experienced professionals would not expect even from a midrange DSO manufactured by one of the "big boys" and costing more than 10 times as much

Just like the majority of modern DSOs, this one does not have a "real" input ground. So checking anything with input coupling set to GND is completely meaningless.

If you want to check the offset with grounded input, you could use a BNC-Terminator for that (with DC coupling). Or just leave the input open, the difference is really negligible.

If you do so, please check the specifications for offset and gain error in the data sheet (and compare these with even much more expensive instruments) before you start questioning the quality of the (excellent - high sensitivity, low noise) frontend, just because you spot a few pixels deviation somewhere.

Self calibration is there to bring the instrument to the calibrated state. Specifications can only be guaranteed after a self-cal has been performed after at least half an hour warm-up of the instrument. You can bet your bottom dollar that the factory performs such a self-cal before checking the instrument cal state and then issuing the certificate if it's passed. Of course you won't need another self-cal anytime soon unless there were major temperature changes or the firmware has been updated. Yet the temperature in your lab might differ from the one used for the calibration, so a self-cal could improve things.

Self-Cal cannot provide infinite accuracy though. It relies on an internal reference and a highly accurate DAC, but the adjustments don't have infinite resolution. This is true for the offset DAC (for offset calibration) as well as the PGA (for gain calibration). So especially if you look at the trace at high sensitivities (<5 mV, which are just "fake" software zoom in many other even much more expensive DSOs, but are very real in the SDS1000X-E series), the limited resolution of the offset DAC might leave us some visible offset in the realm of a couple 100 µV.

The frontend of a modern DSO has to use an OpAmp for the DC/LF-path of the input buffer. Since it needs to be high impedance, it has to be (MOS)FET. But this means that it cannot be low offset with low TC - and you don't want a chopper stabilized amp in the frontend of a DSO. This is the reason why a DSO frontend cannot be compared to a multimeter, because the latter usually doesn't need a separate OpAmp and even if it did, it would be of the "zero offset" species. It's essentially the drift and temperature stability of this beforementioned OpAmp that causes the offset error (changing with temperature) in a DSO, hence makes the self-cal necessary. The SDS1000X-E can even provide a "quickcal" that kicks in automatically as soon as the instrument detects a condition that might increase the offset error. The gain on the other hand is much more stable anyway.

If you are interested in an exemplary performance verification regarding DC and AC accuracy, you can have a look at the document "SDS1104X-E Review 50-70.pdf" that is attached in reply #1 of this thread:

https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/

In this document, at page 52 you will find a demonstration to measure a DC voltage of 205 V to an accuracy of better than 0.08 %.
Compare this to the specifications and you will learn that this instrument can actually be vastly better than that, especially when it comes to offset accuracy. Still you'll have to live with a small additive error, only visible at high sensitivities.

Thanks very much. Self calibration seems to have helped.

I appreciate your in-depth review and have a lot of reading to do.

[tautech]

Thanks for pointing this out. I was relucatant to run a self-cal, at least until I've seen a factory calibration certificate, in case I overwote that factory cal.

There's nothing to "overwrite", there's really no such thing as a "factory cal" in a device which recalibrates itself at the push of a button.

Oh FFS what BS your random reply generator is creating this time only this time it's absolute BS ! 

Pretty obvious you have never seen a calibration certificate or even know about the processes used in modern closed box calibration.
Traceable calibration certificates are required to list the instruments SN# and the instruments used for the calibration process, their SN#'s and the expiry date of their calibration.
All this is included on Cal certs accompanying Siglent instruments.

Please disable random reply generator and enable any critical thinking residing in that space between ears.

[Fungus]

Pretty obvious you have never seen a calibration certificate or even know about the processes used in modern closed box calibration.
Traceable calibration certificates are required to list the instruments SN# and the instruments used for the calibration process, their SN#'s and the expiry date of their calibration.
All this is included on Cal certs accompanying Siglent instruments.

Factory Calibration certificates, exist, obvously. I've seen one. There's samples on the Siglent web site.

eg. https://siglentna.com/wp-content/uploads/2018/09/SIGLENTCoCSample.pdf

Note that they don't give any numbers, it's just pass/fail.

What doesn't exists is some burned-in "factory cal" parameters inside the 'scope that could be 'overwritten'. Factor calibration isn't some magical process, they just pressed the self-cal button at the temperature/humidity stated on the certificate and unless you're working at that exact temperature/humidity you should really recalibrate it as soon as you receive it.

Try reading the words on the screen before rushing to insult me.

[tautech]

Pretty obvious you have never seen a calibration certificate or even know about the processes used in modern closed box calibration.
Traceable calibration certificates are required to list the instruments SN# and the instruments used for the calibration process, their SN#'s and the expiry date of their calibration.
All this is included on Cal certs accompanying Siglent instruments.

Factory Calibration certificates, exist, obvously. I've seen one. There's samples on the Siglent web site.

eg. https://siglentna.com/wp-content/uploads/2018/09/SIGLENTCoCSample.pdf

Note that they don't give any numbers, it's just pass/fail.

What doesn't exists is some burned-in "factory cal" parameters inside the 'scope that could be 'overwritten'.

Try reading the words on the screen before rushing to insult me.

So lets review information already presented in this thread as it seems this has yet to be enabled:
Please disable random reply generator and enable any critical thinking residing in that space between ears.

Posted by: tautech
« on: Yesterday at 09:40:25 am »
To confirm this assumption the factory says:
The user self cal will not destroy the calibration data.

Note that they don't give any numbers, it's just pass/fail.

The numbers that must be met are in the datasheet and in greater detail in the Performance Verification section of the Service manual.

[Fungus]

Note that they don't give any numbers, it's just pass/fail.

The numbers that must be met are in the datasheet and in greater detail in the Performance Verification section of the Service manual.

Yep, that'd be how they do the "pass/fail" part.

(or maybe you think they do it randomly?)

You finally seem to be getting the complete picture.

[tautech]

You finally seem to be getting the complete picture.

Oh really, do you think so ?

Service manual P23 Performance Test
https://int.siglent.com/upload_file/user/SDS1000X-E/SDS1000X-E_ServiceManual_SM0101E-E01A.pdf

[Fungus]

Oh really, do you think so ?

You haven't actually disagreed with any of my "random" replies so I'm starting to hope so. 

[tautech]

Oh really, do you think so ?

You haven't actually disagreed with any of my "random" replies so I'm starting to hope so. 

RTFM 

[74HC04]

Update: The distributor sent me a jpeg scan of the front page of the Calibration Certificate.

The distributor in question is Telonic. As you will see from the few pages of the following thread leading to the one linked below, this is not the first time they've sent a Siglent instrument without it's Calibration Certificate. I can only speculate as to what happened to the document but would recommend that anyone ordering from Telonic that values their Cal Cert insists that it is included within the scope of delivery!

https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/1650/.

Thanks all for your input and advice.

[74HC04]

...included within the scope of delivery!

Freudian slip!