Query for PXI 6031E

[Sarang Jaiswal]

Hey All,

I have just started with all the PXI stuff. I have a very basic query for PXI 6031E.

I have a query for PXI 6031E. The sampling Rate is 100kS/s. My doubt is if I am using 2 channel then the sampling for that channel is 50kS/s  each  is it true or is it 100kS/s for each channel ???  

In you have any information about this please forward it to me

Thank you.

[devchander]

hi Sarang

PXI 6031 is an Eseries card and has a single ADC which all AI channels share.

As you rightly understand, while using 2 channels, the max scampling rate you can configure will be 50kS/sec.

The max possible sampling rate for a channel in a scan list = maximum scan rate of card / by number of channels in the scan list.

regards

Dev

[Sarang Jaiswal]

Hey thanks for the reply, I would also like to know the following.

I want to acquire 20KHz Pulse Waveform in LabVIEW applied from the function/waveform generator. I am using PXI 6031E for acquition. The waveform must be acquired continuously.

I want to know what should be the value of

sample per channel                     --->  of DAQmx Create Channel

Rate                                                --->  of DAQmx Create Channel

Number of sample per channel  --->  of DAQmx Read

If I put the values as

sample per channel                     =  3000   

Rate                                             =  30000

Number of sample per channel   = 3000

then the detected frequency in LabVIEW is approx around 10K though I am providing 20 K ..... why is this happening ??

I hope you all have got my question. In case of any more clarification please let me know.

Thank You.

[McKala[DE]]

Hello Sarong,

Don't forget the Nyquist Theorem (this gets lots of people).  With a 20KHz signal, you have to sample at at least 40KHz to avoid aliasing.  While 40KHz is the minimum rate needed to reconstruct the signal, I would recommend sampling at 80-100KHz for better resolution. 

The values of each input is application dependent, below is a description of what each input does.   

The "Samples per Channel" input on the DAQmx Timing VI creates a buffer for your data.  When acquiring a continuous signal, it is better to leave this unwired and the driver will set this.  

The "Rate" input on the DAQmx Timing VI is the sampling rate - for your application it needs to be greater than 40KHz.

The "Samples to Read" on the DAQmx Read VI specifies how many samples to retrieve from the buffer at one time.  You can choose to read a certain number of samples or if you leave this unwired you will retrieve all the samples available in the buffer. 

Hope this helps!

 

[Sarang Jaiswal]

Hey Micaela,

Thanks for replying. I tried out from 40K-80K but i am not getting the waveform continuously on Charts.....I really don't understand why ... my main problem is i have to aquire signal from 400 - 20KHz .....so maximum frequency component is 20Khz ......hence according to nyquist the sampling frequency comes around 40KHz ....

if you can send me the sample program it would be nice.....i am using PXI 6031E

thank you

[McKala[DE]]

Sarang,

Take a look at the shipping example Cont Acq&Graph Voltage-Int Clk VI. 

You can get to it through Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Analog Measurements >> Voltage >> Cont Acq&Graph Voltage-Int Clk (about 6 from the bottom). 

Also, you might try using a Waveform Graph instead of a Waveform Chart.

[Sarang Jaiswal]

hey Micaela,
I already tried with that example. Its not working ..... also i am using Charts and not Graph's . I will post my vi tommorow as my Lab is closed now .

Thank you

[devchander]

hi sarang,

Using a graph will help you as chart stores values and uses virtual memory

I would suggest one more thing.

Althrough Labview DasqMx  will automatically allocate a suitable buffer size for continous acquisition, i would advise you to try using a AI buffer of suitable size, preferably 4 times the sampling rate.

if you could tell what error you were getting, it would be a help.

regards

Dev