Can I acquire singals of frequency greater than 200KHz using 7831-R FPGA module without loss of data?

[keyur.ospl]

hi all

can anybody help me

i would like to aquire signal of frequency greater than 200k Hz using 7831R FPGA module

if anybody have souce code of vi then plz help me to solve this problem

keyur makadia

application engineer

Optimized Solutions Pvt.  Ltd

[xseadog]

Hi

in a nutshell NO

If you care to read the User Manual

http://www.ni.com/pdf/manuals/370489a.pdf

It states the max  sampling frequency at 200KS/s.

If you understand the Nyquist Theorum then your max frequency would be  100Khz. Then the samplied signal would be a pure as throretical possible with out any images.

xseadog

[MattP]

xseadog is absolutely correct if you want to acquire an analog signal.  You can sample a digital line at 40 MHz, but the analog inputs are limited by the on-board analog to digital converter.  It is possible, however, to build an external circuit with a faster ADC and sample the ADC's digital outputs at a faster rate than 200 KS/s using the 7831's digital inputs. 

There will be no programmatic solution, but it is technically possible (though not ideal) to implement a hardware solution as above. 

[Vineet_A.]

Hello,

There is one other option that you might consider.  Using the R Series expansion system, you can sample faster with the NI 9221 or NI 9201 C Series modules.  The crow-9151 chassis can connect to one of the digital connectors on your 7831R, and those modules can sample up to 480kS/sec on a single channel with R Series.

Here are a few links to the hardware I mentioned.

https://www.ni.com/en-us/support/model.ni-9151.html

https://www.ni.com/en-us/shop/model/ni-9201.html

https://www.ni.com/en-us/shop/model/ni-9221.html

Regards,

Vineet A.

[MakOnTrack]

The NI-7831 Hardware specification says, that each input can be independently sampled at a max. frequency of 200kHz. (-> 5 usec per sample)

Is it possible, that I connect a same analog signal to, say 5 different Analog I/P lines of the 7831R; acquire data from each channel parallelly (making use of independent data acquisition loops). But I synchronize the 5 acquisition loops such that, none of them acquire data at the same instant of time.

Making use of this architecture, I will potentially get 5 different samples in a single 5 usec period. That will make my sampling frequency multiply by 5, i.e. 1000kHz.

I haven't tried it yet, so don't know whether it will work. But has anyone tried ? Or probably knows why this isn't possible ?

TIA.

--

Makarand Mijar
Final Year, M.Tech [Power Electronics]
5-Year B.Tech-M.Tech Dual Degree
Department of Electrical Engineering
IIT Kanpur, India.
Email: makarand@iitk.ac.in

[Vineet_A.]

Hello,

It is possible to do what you're describing in LabVIEW FPGA, and achieve an overall higher sampling rate.  I've never tried it myself, but I'm pretty sure I've heard of others that have.  You'll have to be very careful when triggering and synchronizing your parallel loops in order to get it just right.

If all you need is a faster sampling rate, you could also use one of the new PXI-7851R boards, which can sample at 750 kS/s on every channel.  If you alternate between two only channels, you could get up to 1.5 MS/s and the programming would be a lot easier.

Here's a link to the model page >> https://www.ni.com/en-us/shop/model/pxi-7851.html 

Regards,

Vineet

Message Edited by Vineet A. on 07-17-2009 04:51 PM