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Sampling Problem with Flexrio

Hi ,

 

I have Problem with Flexrio. I get signal parts that do not exist normally. Here is a picture.

 

Thanks

 

 

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Message 1 of 7
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Hi labview_jumper,

 

I'm assuming that you're use to cRIO or R series since the FPGA code you're showing (right?).

Actually, Analog FlexRIO adaptor Modules have their own clock, so you usually want you're AI node to be inside a SCTL running at the AI Clock rate.

 

Which module are you using? I'd suggest with give a try to the LabVIEW example associate to that module, that will give the architecture basis you should respect to use your FlexRIO.

 

Have a good day,

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Hello ,

 

I am using NI 5752  with 7966R. I am also getting wierd signal shapes even when running their example programs. I can see that gain is varying at different frequencies even without any gain control implementation. What may be the reason for this? Any idea?

 

 

Thank you,

Mithun

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Hello Mittu1,

 

I dont mind you post on that thread but you might get more answer creating a new one 😉

 

concerning your issue with the 5752, this make me think about an issue I have faced.

Can you tell us more about the signal you're sampling? The 5752 is design for ultrasound so there is a filter with a 16KHz cutoff frequency.

(see http://www.ni.com/pdf/manuals/375573a.pdf or http://www.ni.com/pdf/manuals/373035b.pdf).

 

So you cannot trust any result you're seeing about the gain if your signal frequency is lower 16KHz.

I hope this help.

Have a great day,

Message 4 of 7
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Hi Florent,

 

No i am working with ultrasound signals. If coming below 100 KhZ signal amplitude is very much high and at higher frequencies above 1 MhZ, it is coming down drastically. Really wierd behaviour. Can you suggest me any way to solve this?My signals are in the range of 200 khz to 6 MhZ. With very low amplitude..Say 10 mvpp.

 

 

Thank you,

Mithun

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Hi Mittun,

 

did you try to use the 5781 example in which you can configure the ADC? Which anti-aliases filter do you use (7.5MHz, 10MHz or 14MHz)?

That can explain a lot about the amplitude variation you're seen 🙂

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I tested NI 5752 with PXIe-7961R by using ConfigureDAC example.

Input signal is square wave of 500 KHz through SMB-2145.

Output is not square wave but half square half triangle wave.

I attach the photo of output wave.

 

I don't known how to solve this problem.

Do you know how to solve its? Please tell me if you know.

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