6074BD - offset errors

OASJ2YSeeEhBQo1

Ok, so after many tests (I won't describe all them, it is not important) I am 100% sure that the offset problem is cause by a bug in the PC software and I found a temporary fix for it, at least until Hantek release an update.

The bug affects the version 2.2.4 of the software available for download on the product's web page. To fix the offset, install an older version (I've used Ver. 2.1.36, included in the CD) and run the calibration routine, done.

Result of the calibration using Ver. 2.2.4 of the software:



The same scope after re-running calibration using Ver. 2.1.36:


I want a beer

OASJ2YSeeEhBQo1

Dear Amy,

Please let me know when you have the software update ready with the fix, I'm needing that.

thx

amy

Sir, yes, we found that there was a bug with the software. Oue engineer planned to finish the modification by the end of this week.
Please wait a while.

OASJ2YSeeEhBQo1

I've being doing some more tests with a 6074BE and I think I may have found the problem, well at least one of them...

I am almost convinced that the main cause of this offset error is a software problem. I noticed that the initial position of the channel's cursor (the arrow on the left) on the screen influences the results of the calibration. Setting the cursors at the center of the screen before start the calibration yields the best results for me. I also noticed that changing the time/div to below 1us increases the offset. Changing the power supplied to the scope also has influence, so the thing is not so simple...

I am planing to do a more systematic test later and I'll report back with more details.

gf1

OASJ2YSeeEhBQo1 replied at 2019-3-24 12:15
I got in contact with Hantek by e-mail and they replied with one possible solution.

Try this: conne ...

Thank you, I will try...

OASJ2YSeeEhBQo1

I got in contact with Hantek by e-mail and they replied with one possible solution.

Try this: connect the black connector of the USB cable to your computer and the red one connect to an external power supply (like an USB charger) but it must be a good one, capable of supply 5V@2A then try the calibration again. For my case it helped and I can see an improvement although some offset still visible in the lower volt/div settings.

Apparently the problem is related to insufficient power being supplied to the device.

gf1

When I look at the PCB photos available in the internet, then V/div attenuators, ADC driver, channel multiplexer look quite different in the 2000 and 6000BD series. One common sub-circuit is obviously the dual-path input buffer amplifier, which uses a discrete FET source follower on the fast AC path, and an AD9510 on the DC path. This sub-circuit seems to be present - with small variations - in several scopes (IIRC also in some Rigol ones).

gf1

OASJ2YSeeEhBQo1

Does the 6074 scopes and the new Hantek2000 share a similar frontend or piece of firmware? I'm asking because I am observing a similar problem with my 2D42 and as gf1 noticed, I can clearly see the offset of trace or waveform changing as I change the scale setting or turn on/off a channel. Calibrating didn't help as well.

I will try to make a quick video later to better illustrate the issue.

gf1

I do not see a statistically significant difference with open inputs and 50 Ohm terminated inputs. The resulting offsets vary anyway when I run the calibration multiple times in sequence. And after a calibration run, the residual offset is not invariant either, for each channel, but varies with the set of enabled channels, V/div, time/div and bandwidth limit setting.


[ It were certainly not the best idea, though, to keep the probe connected and to short the ground lead to the probe tip, since this "loop antenna" may pickup noise from the environment. ]

gf1

Han

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