Data acquisition and representation on waveform graph

[Triciakenf]

 

 Hello ,

i'm doing data acquisition from a scope via GPIB but i keep having zeros between points which i don't want. I attached the picture of the wave from the scope and also a picture of my waveform graph  as well as the points recorded in text file to show these zeros. How can i remove the zeros so as to have a smooth curve? 

I also noticed that the value of the voltage on the waveform graph(up to 100v) is not exactly what i have on my scope(20mV/div) . Is there a way to get the exact scaling?

Thanks,

Patricia

[pincpanter]

Probably, every voltage value is long two bytes rather than one. Check the scope documentation thoroughly.

EDIT: I managed to open a Teledyne scope programming manual, which may be similar to your device. According to the manual, waveform values you get must be linearly rescaled using two parameters (vdiv and ofst) that can be queried from the scope.

[RTSLVU]

A couple things here...

1. How are you retrieving the scope sweep data?
2. Why do you convert it to a U8?
3. Most scopes I use return Floating Point numbers (usually a double) for sweep Y values

I am guessing you are requesting the sweep data wrong or it is in a different format than you think it is.

Also what scope are you using? Most popular scopes have a set of LabVIEW "drivers" that make this type of operations much easier than using raw SCPI commands.

[Triciakenf]

Thanks for your reply.

I'm not sure if i understood your questions correctly but i will try to answer them.

 My oscilloscope (Teledyne Lecroy LT342L) is in RIS mode and i use the waveform command (WF?)  to obtain the wavedescription of my signal. The output is a string in ASCII code(you can see how it looks like on the front panel in the picture i attached previously) which can't be plotted on a waveform graph. So i used the vi change string into array (U8)  which returns just unsigned bytes. Since i have negative values too i had to wire it to sign bytes also to be able to view the negative part of the plot.

I dont use the Labview drivers because the version available for my model is 2016 and not compatible with labview 2021.

[pincpanter]

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@RTSLVU  ha scritto:

1. Most scopes I use return Floating Point numbers (usually a double) for sweep Y values

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This does not seem to be the case. Values are most probably U16 or I16.

[RTSLVU]

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@Triciakenf wrote:

I dont use the Labview drivers because the version available for my model is 2016 and not compatible with labview 2021.

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Well that makes no sense at all because that vast majority of LabVIEW drivers are just the SCPI commands wrapped up in pre-fab VIs.

I use Lecroy scopes daily, our Waverunner 44XI scopes are almost a decade old and the LabVIEW drivers from when we bought them still work just fine with LabVIEW 2020...

[Triciakenf]

Well i tried it out and it was not compatible so i had to use IVI drivers for many models listed. just 2 models listed were tested and mine isn't among. I sent a mail to ni drivers department and this is what i got as answer 'The current LabVIEW wrapper given in the download page only supports 2016 '. Well they are working on it but i in the meantime i have to continue working on my project.

[RTSLVU]

Oh sorry, I just noticed these are IVI drivers. I have never had good luck using any IVI driver.

But back to the original issue... I am still guessing that you are getting either both channels' data or the format is not what you expect it to be.