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Author Topic: Rigol DS1054Z Cursor Position Error  (Read 1501 times)

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Offline alsetalokin4017

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Rigol DS1054Z Cursor Position Error
« on: December 14, 2015, 08:15:45 PM »
Grr.

I was doing some checking of scope math and the results from manual calculations using Cursors didn't quite jive with the scope's automatic Measurements. Looking more closely it seemed that the Cursor positions were being reported a little off. So I checked it out without any waveforms on screen to complicate matters. See the screenshot below for the errors in the Vertical Cursors (horizontal lines measuring vertical values). The CH1 baseline marker is exactly on the screen centerline (0.000V offset) and the Cursor B is also positioned right on this line, so it should be reporting 0.000 V but it actually reports -100.0 mV. The Cursor A is positioned exactly on the -10V line but the position is reported as -10.20 V.

This is right after running a Self-Calibration routine, too. And I get similar results from using other channels and different vertical scales. The Cursor positions are reported incorrectly! Not by much you might say, but enough to throw off calculations by a significant amount.
The easiest person to fool is yourself. -- Richard Feynman
 

Offline TomThomas

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Re: Rigol DS1054Z Cursor Position Error
« Reply #1 on: December 15, 2015, 12:16:41 AM »
Hey....
what about:
5V/div * 8div =40V
40V/2^8bit = 156.25mV/bit

How should the scope measure more accurate?
Regards
Thomas
 

Offline dcac

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Re: Rigol DS1054Z Cursor Position Error
« Reply #2 on: December 15, 2015, 03:22:43 AM »
@alsetalokin4017

Yeah there seem to be a (small) vertical scaling/offset error between the graticule and the cursor values.

Here I've ground coupled CH1 and pressed vertical position to set GND reference at 0V and this matches exactly with the graticule center line, set Trig level to -15.0V and this also matches the graticule perfectly.
But cursor A which is exactly on top of the GND line reports -0.100V and cursor B which is exactly on top of the Trig line reports -15.20V.

So cursor A has to be moved 1 pixel up to show 0V,  and cursor B moved 2 pixels up to show -15.00V, but then they no longer matches the graticule exactly.

 

Offline alsetalokin4017

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Re: Rigol DS1054Z Cursor Position Error
« Reply #3 on: December 15, 2015, 09:19:53 AM »
@dcac
Thanks for checking. It seems that this is not just my scope then.

@TomThomas
It's not so much the lack of precision due to the 8-bit ADC, it's the lack of agreement between the Cursor's reported _position_ and what the scope's Measurements come up with, or where the Cursor is actually located.

Try giving the scope a DC signal and use the Measurements to report things like Peak and Average voltages. Then put the Cursor on the trace and see if the reported Cursor position agrees with the Measurements. If the issue was merely the precision of the ADC, one might expect that the Cursor value would still agree with the Measurements if the Cursor is in the same place as the trace. But it doesn't.

The easiest person to fool is yourself. -- Richard Feynman
 


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