VI for capturing data at high frequency

[Dhawal]

Hi,
I have been trying to build a VI, which would read data from a machine at around 50KHz. I am accepting one analog signal from this machine, converting into digitized values and storing ALL the digitized values into a file. I could not afford to loose even one data. I would really appreciate if anyone has an example as to record data at such a high frequency.

Thanks in advance

Dhawal

[mikeporter]

One channel running at 50kHz is simple - in fact in the world of DAQ it's not even very fast. Check out the examples for seamless data acquisition. Basically, the idea is to set up a circular buffer that the DAQ writes to and LV reads from. As long as LV extracts the data faster than the DAQ is inserting it the process can run forever.

Mike...

[Dhawal]

Hi Mike,
Thanks for the reply. I was trying to search for the example that you asked me to look at. I really dont know where to find it. I would appreciate if you could attach the VI, so that I could understand what exactly am I suppose to do.
I am just trying to gather all the data, and would want it to open it in excel sheet (if thats possible). I had read that it is advisable to open such a huge file by initially collecting the values into binary form and then opening it into excel, once the acquisition is over.
Please suggest on the same, and also please try and attach a Vi for the same.

Thank you.

Dhawal

[Dennis_Knutson]

First, what are you using to acquire this data? Is it an NI-DAQ board, GPIB, serial, something else? If it's an NI-DAQ board, there are several examples. Open the example finder and expand Hardware Input and Output>DAQmx>Analog Measurements>Voltage.

Second, how much data are you acquiring and for how long? Excel is a pretty poor choice for saving large amounts of data. The old limit was about 65000 rows. I think microsoft has increased this with the latest version but you still won't be able to store much.

[Dhawal]

Hi Dennis,
I am using NI DAQ board (and am using Labview 8.2.1). I am trying to gather data at a rate of 30khz for around 10 sec (which would be around 300,000 samples/ch). You were very much right about microsoft excel, it just reads data to about 65000 rows. I cannot afford to loose any data in the experiment that I am running.
I would also want to draw FFT of the signals in real time. Is it possible?

Please suggest.

Dhawal

[Dennis_Knutson]

A qualified yes. I quality the answer because you use the term 'real-time'. Windows is not a deterministic operating system so 'real-time' does not apply. But, if by 'real-time', you mean analyzing the signals as they are acquired, then you should be able to do this. Again, do a search of the shipping examples for 'FFT'. You might also want to look at some of the design patterns (File>New...). You could have the acquisition in one loop and the analysis/graphing in another.