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DSO-X 2012A WaveformGenerator problem

Question asked by lc_bszet_dd on Jan 7, 2013
Latest reply on Jan 9, 2013 by lc_bszet_dd

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Hello.
After updating the DSO-X 2012A to the latest firmware, i found a rather curious problem, unsure if it's caused by the WFG, or by a lack of coffee on my side.
Connected the WFG-OUT to the CH1-IN using a 50Ohms cable, set the WFG to 1kHz square wave, Hi-Pot=1V, Lo-Pot=0V, Impedance=50Ohms.
On measuring the signal, the scope shows me a signal with 2Vpp, instead of the 1Vpp as expected.
Attached the display of the measured signal, with WFG settings still shown.

So the question arises, should i rather go to bed and call it a day, or is this supposed to be this way?

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ed Jan 7, 2013 3:11 PM

With the WAVGEN set to 50 ohms it expects you want 1Vpp into a 50 ohm load.
So its open circuit voltage is 2Vpp which is what you are seeing with CH1 set to 1Meg input impedance.

Set CH1-->Impedance-->50ohms.
Then it will show 1Vpp into the 50 ohm scope impedance.

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lc_bszet_dd @ ed on Jan 9, 2013 9:30 AM

Ahhh, so the device did outsmart me for good.
Thank you for solving that mystery of mine.

The only thing i couldn't quite get to work was changing the impedance of the channel.
Not that it would matter, as i now know to leave the WFG at High-Z.
But i couldn't find any option in the channel menu for changing the input impedance.
There is no soft button labelled with "Impedance" in the channel menu.
If you could give me another nudge, so i do find that option, i'd be very grateful.
Thank you again, in advance, for your help.

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algoss

@ lc_bszet_dd on Jan 9, 2013 9:50 AM

The input impedance on the 2000 series of scopes is fixed at 1M. It is switchable, between High-Z and 50 Ohms, on the 3000 and higher families of scopes.

Starting with the 90000 series of scopes, it is fixed at 50 Ohms.

Al

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lc_bszet_dd @ algoss on Jan 9, 2013 9:52 AM

That would explain the certain lack of the option to change the input impedance.
Thanks a lot for the really fast reply.

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4 Replies

ed Jan 7, 2013 3:11 PM
Mark Correct
Correct Answer
With the WAVGEN set to 50 ohms it expects you want 1Vpp into a 50 ohm load.
So its open circuit voltage is 2Vpp which is what you are seeing with CH1 set to 1Meg input impedance.

Set CH1-->Impedance-->50ohms.
Then it will show 1Vpp into the 50 ohm scope impedance.
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- lc_bszet_dd @ ed on Jan 9, 2013 9:30 AM
  Mark Correct
  Correct Answer
  Ahhh, so the device did outsmart me for good.
  Thank you for solving that mystery of mine.
  
  The only thing i couldn't quite get to work was changing the impedance of the channel.
  Not that it would matter, as i now know to leave the WFG at High-Z.
  But i couldn't find any option in the channel menu for changing the input impedance.
  There is no soft button labelled with "Impedance" in the channel menu.
  If you could give me another nudge, so i do find that option, i'd be very grateful.
  Thank you again, in advance, for your help.
  Like • Show 0 Likes0
  Actions
  - algoss @ lc_bszet_dd on Jan 9, 2013 9:50 AM
    Mark Correct
    Correct Answer
    The input impedance on the 2000 series of scopes is fixed at 1M. It is switchable, between High-Z and 50 Ohms, on the 3000 and higher families of scopes.
    
    Starting with the 90000 series of scopes, it is fixed at 50 Ohms.
    
    Al
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    - lc_bszet_dd @ algoss on Jan 9, 2013 9:52 AM
      Mark Correct
      Correct Answer
      That would explain the certain lack of the option to change the input impedance.
      Thanks a lot for the really fast reply.
      Like • Show 0 Likes0
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DSO-X 2012A WaveformGenerator problem

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