Labview does not read the amplitude of waveform correctly for TDS 2014 scope

[ngautam]

Hi, 

I downloaded drivers for tektronics TDS 2014 oscilloscope from NI website (http://sine.ni.com/apps/utf8/niid_web_display.download_page?p_id_guid=047216EC20B66FABE0440003BA7CCD...  ).  I am trying to collect waveform from the oscilloscope. I am able to talk to the oscilloscope and see the waveform on my computer. However, the waveform displayed has 10 times higher amplitude than the actual waveform. I have set the Probe attenuation to unity and I am not sure what makes this change in the waveform. 

The vi I have been using is attached here.

Thanks for your help!

Nutan

[Albert.Geven]

If you have a 1..10 probe and the scope knows this then the signal is multiplied by 10 also on the scope.

BUT maybe twice multiplied?

[ngautam]

I chcked the output value also of the probe and that tunrned out to be the same as what I set it to.

I am not sure where the multiplication is taking place.

[Dennis_Knutson]

Are you saying the amplitude display on the pc is different than the amplitude display on the scope?

[ngautam]

Before connecting scope to computer, the amplitude ons cope is 200mV. After connecting scope to computer, the amplitude on computer is 2V and during the acquisition process, the axes on scope are also adjusted such that it also reads 2V.

[Dennis_Knutson]

Connecting to the computer will not change anything. You must mean connect and run the VI. There is a probe setting being sent to the scope. I can't look at the VI right now so just probe around with context help turned on. You'll find it.

[ngautam]

Yes, I meant opening the labview and running the VI, that changes the amplitude. I have looked at the probe settings in VI in the context help and could not find anything suspicious there. I will try to look at it again, thanks

[fredericb]

Hi 

I had a similar problem using an agilent DSO serie scope and Labview.

It turned out that in my case the scope reading from labview was a simplified data file a bit like like a screen shot of your scope screen instead of the real data. You can check by comparing the number of points displayed on your VI and the time scale and resolution of your scope.

Anyway after messing about for a while i decided it would be faster and more reliable to use the software provided on the agilent website (even tho it's a bit crap) at least you can get the real data out of your scope and do a post process analysis of them.

Fred

[crossrulz]

Your code is changing the probe attenuation to 10 (default value on the control is set to 10).  If your scope was previously set to 1x probe, then that will cause the change from 200mV to 2V.

[ngautam]

Thanks! I will look into that.