VOLTCRAFT DOV series

[Martin72]

Hm-hm...
I'll probably take a closer look at that tomorrow....
DC measurement, source SDG6052X, once at 50 mV DC, once at 300 mV DC.
The result is somewhat poor across all channels (also measured on Channel 1).
It’s interesting that in both voltage cases, the deviation is about 13 mV—is this due to the principle involved?
As I said, I’ll look into this in more detail tomorrow or later today.

[Aldo22]

Hm-hm...
I'll probably take a closer look at that tomorrow....
DC measurement, source SDG6052X, once at 50 mV DC, once at 300 mV DC.
The result is somewhat poor across all channels (also measured on Channel 1).
It’s interesting that in both voltage cases, the deviation is about 13 mV—is this due to the principle involved?
As I said, I’ll look into this in more detail tomorrow or later today.

I can't agree with that.
I think the DC accuracy is on par with a simple DMM and is definitely sufficient for an oscilloscope.
Attached 30mVDC, 300mVDC

I took a look at the AC accuracy here:
https://www.eevblog.com/forum/testgear/voltcraft-dov-series/msg6277190/#msg6277190

The accuracy is one reason why I kept this scope.
I think that at frequencies above 10 kHz, many benchtop DMMs aren’t any more accurate.

[Olex]

I don't have any issues with the measurements either.
It might be a calibration issue.
What value does the DVM show with shorted probes?

[Martin72]

I hadn't thought about the self-calibration; I'll do that first thing later.

[Martin72]

I think I've found the problem—the scope doesn't like my DC source....
Thanks for responding so quickly; otherwise, I would have had to spend a little longer trying to figure out the problem.
Well, for whatever reason, this source isn't working—but that also means I don't have another mV source, so I'll have to change that... and see where I can find one.

[Aldo22]

I think I've found the problem—the scope doesn't like my DC source....
Thanks for responding so quickly; otherwise, I would have had to spend a little longer trying to figure out the problem.
Well, for whatever reason, this source isn't working—but that also means I don't have another mV source, so I'll have to change that... and see where I can find one.

It doesn't have to be expensive.
I use my FNIRSI SG-003A for this kind of thing and check it with the ZT-225.
The SG-003A is a device I never would have thought I'd use so often.

[the Chris]

I think I've found the problem—the scope doesn't like my DC source....

Did you attach it directly? You can probably switch between 50Ohm Output and "HiZ" or something similar on the SDG6052X. Problem is that the HiZ option does not necessarily mean 1MOhm input and this causes deviation between what you set on the FG and what you see on the scope. If you use a probe with an BNC adapter, the value should match again.

[Martin72]

The voltage drops when the scope is connected; the multimeter displays an exact value.
Another scope does too, though.
@Aldo:
I ordered it; it should arrive tomorrow...

[Aldo22]

The voltage drops when the scope is connected; the multimeter displays an exact value.

That’s weird—there should be 1 MΩ at the input.
Is it the same with the probes (or without them)?

@Aldo:
I ordered it; it should arrive tomorrow...

Hehe! 
It's a Fnirsi. It's not perfect—it's a bit unstable in the lower mV range, and it takes some getting used to if you want to explore all its features—but it's really OK for the price.
Sometimes I also use it as a portable power supply when 24mA is enough.  In any case, you can’t do much damage while testing things at that current.

[Martin72]

That’s weird—there should be 1 MΩ at the input.
Is it the same with the probes (or without them)?

The 1M Ohm are also there, but something seems to be interfering with each other.
For example, when I set the generator to 0V, a multimeter also reads 0, but the DOV reads -10mV—which is really strange.
If things go better with the Fnirsi tomorrow, I don't want to spend too much more time on this.

it's a bit unstable in the lower mV range,

That doesn't surprise me; there's also a generator with a mV range, but it has a delivery time of a few weeks—but I didn't want to wait that long, so I ordered this Fnirsi.
However, I'm fairly certain that I'll fill this gap in my collection in the medium term, specifically regarding voltages in the mV range.

[Olex]

For example, when I set the generator to 0V, a multimeter also reads 0, but the DOV reads -10mV—which is really strange.

What does the DVM in the oscilloscope show if you short the probe or BNC?

[Martin72]

 

Not enough...

[Olex]

Not enough...

Yeah, it's pretty much the same for me at lower values, but at higher ones, discrepancies up to hundreds of millivolts start to appear.
I want to try tweaking the calibration settings in the service menu, but first, I'll wait for a decent fan - I ordered a Noctua one.

[Aldo22]

Yeah, it's pretty much the same for me at lower values, but at higher ones, discrepancies up to hundreds of millivolts start to appear.
I want to try tweaking the calibration settings in the service menu, but first, I'll wait for a decent fan - I ordered a Noctua one.

I don't see "hundreds of millivolts.”
At 23V, I see a deviation of <100mV.
That's less than 0.5%.
What do you expect?
Oscilloscopes aren't exactly the best tools for measuring VDC. 

[Martin72]

Yeah, it's pretty much the same for me at lower values, but at higher ones, discrepancies up to hundreds of millivolts start to appear.
I want to try tweaking the calibration settings in the service menu, but first, I'll wait for a decent fan - I ordered a Noctua one.

Thumbs up for the Noctua fan; as for the rest, I'd be cautious if I were you.
You can't expect a µV offset in the V range—the resolution isn't high enough for that.
The 4-bit resolution is more of a gimmick than anything else.
I'd leave the calibration data alone.

[KungFuJosh]

Why leave it alone?  If he can back up the cal data, it's a low risk.

[Martin72]

There are other factors to consider when taking measurements, such as vertical resolution, the measurement window, etc.
Here are some measurement examples of a 5V reference (DMMplus).

[Aldo22]

There are other factors to consider when taking measurements, such as vertical resolution,

Yeah, but that's normal.
You wouldn't measure 50 mV in the 500 V range with a DMM either.
The DOV doesn't have a continuous auto mode, does it?
The Hantek can do that.

[Martin72]

Yeah, but that's normal.

You can't say that often enough.

The DOV doesn't have a continuous auto mode, does it?

I don't know—I've already spent more time on the scope than I planned anyway.

[Aldo22]

I don't know—I've already spent more time on the scope than I planned anyway.

I don't think the DOV has that feature.
The Hantek has an AutoRange option. There, you can select X, Y, or XY.
Y scale works similarly to Auto Range on a DMM—always providing an optimal range setting without any further action required.

[Aldo22]

Back to the topic of "High Res":
Under certain circumstances, "High Res" makes a clearly visible difference.
In the two attached screenshots, only the acquisition mode was changed.