Products > Test Equipment
REVIEW - Rigol DS2072 - First Impressions of the DS2000 series from Rigol
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Wim13:

--- Quote from: Teneyes on June 26, 2013, 05:25:54 pm ---
--- Quote from: Wim13 on June 26, 2013, 04:31:45 pm ---
--- Quote from: Teneyes on June 26, 2013, 01:36:18 am ---What happens with the Signal AC coupled, and Trigger DC coupled?
What happens with the Signal AC coupled, and Trigger AC coupled?


--- End quote ---
So in AC mode the trigger signal is not the same level anymore as the displayed signal.
The DSO of course does not know the difference of the AC + DC componont of the signal, so
the trigger in AC mode does not know where the desired trigger level is on the screen. And the orange line is meaningless.

--- End quote ---

Well I tried  modes with and input signal  = a 1 Vpp Sin with 0.5 Vdc offset

when the DS2072 is   Chan 1 AC coupled
                       and  Trigger Setting is set to DC coupled
ACTs the Same as
                              Chan 1 AC coupled
                      and   Trigger Setting is set to AC coupled

So why not show the orange line!!

--- End quote ---

Because it is not the same.....

If trigger mode in in DC, there is a relation with the showed grid on the display ( not the displayed signal )
so the DSO can display a orange line.

If trigger on DC and is on 1 volt, there is a relation with 1 volt on the screen.

But in AC mode there is NO relation the the value next to the displayed grid
and the DSO does not now where to disply the line, so it does not.

In AC trigger mode 1 volt can be anywhere on the screen.

marmad:
"Aliasing is a potential problem in the DSO (Digitizing Storage Oscilloscope): the undersampled, high frequency component assumes the alias (or false identity) of a spurious, low frequency component."

In other words, if the sample rate isn't fast enough, high-frequency components can “fold down” into a lower frequency, causing aliasing in the display.

marmad:
First image is an incorrect display of a 1MHz sine wave @ 5ms/div undersampled at 200kSa/s - causing aliasing (even though anti-aliasing is turned ON).
Second image is a correct display of a 1MHz sine wave @ 5ms/div sampled at 500MSa/s (by increasing the sample length to 56M) - causing no anti-aliasing.
Marc M.:

--- Quote from: Marc M. on June 25, 2013, 07:08:58 pm ---I'll try the RFQ process and hopefully, they'll be a little more responsive thru that channel.
--- End quote ---
I submitted the RFQ this morning and they responded about 4 hours later, including the EEV discount and free shipping :D.  When I tried to pay via PayPal, I was charged shipping.  I did an online chat w/ Dawn and she refunded the shipping back thru PayPal.  In addition, she was able to apply the discount to the DG4162 I purchased earlier in the month prior to learning about Evan's very generous offer.  So while their customer service is lacking thru indirect channels, it's outstanding thru the Quote and Live Chat channels  :-+ :-+.  FWIW, they're estimating the lead time to be 2-3 weeks.  Sounds a bit optimistic but time will tell.
Wim13:

--- Quote from: Teneyes on June 26, 2013, 10:38:14 pm ---
--- Quote from: Wim13 on June 26, 2013, 05:38:10 pm ---
--- Quote from: Teneyes on June 26, 2013, 05:25:54 pm ---when the DS2072 is Chan 1 AC coupled and Trigger Setting is set to DC coupled
ACTs the Same as   Chan 1 AC coupled and Trigger Setting is set to AC coupled
So why not show the orange line!!

--- End quote ---
Because it is not the same.....
If trigger mode is in DC, there is a relation with the showed grid on the display ( not the displayed signal )so the DSO can display a orange line.
If trigger on DC and is on 1 volt, there is a relation with 1 volt on the screen.
But in AC mode there is NO relation the the value next to the displayed grid
and the DSO does not now where to display the line, so it does not.
In AC trigger mode 1 volt can be anywhere on the screen.

--- End quote ---
Does this go back to old Scope devices,
because I would think this DS2000 can determine the trigger value that is used to set the position on the display ,
thus show the trigger level line
Below are 4 displays , (note trigger level in low left corner)
  1.  Input DC coupled  with  trigger DC coupled
  2.  Input DC coupled  with  trigger AC coupled  (no trigger line)
  3.  Input AC coupled  with  trigger DC coupled
  4.  Input AC coupled  with  trigger AC coupled  (no trigger line)

What is the Difference between 3 & 4?
Just my small preference :)

--- End quote ---

The difference is about 100 mV

In picture 3 trigger level is DC+AC, in picture 4 trigger level is AC
if the DC component is 0 or very small, then DC+AC=AC, thats why there is little difference.

More theory:

In DC trigger mode the trigger is fixed, even with no input, the level is fixed and kown.

In AC trigger mode the trigger is dynamic, trigger level is depeding of average AC signal, so not fixed
and its position is not kown.

If in AC trigger mode you change the shape of the waveform, the trigger point will shift, how do you want
this in an orange line on the screen, it will be not steady.

In AC trigger mode the average value of the AC voltage is the 0, this is the reference for the trigger, from there it calculating
the offset. Not from a fixed point.




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