NI Digitizer

[meBaga]

In case of NI digizer 5132, what is the significance of 4MB-ch and 32MB/Channel ?

[Nathan-P]

The difference between these two boards is the amount of on-board memory.  When you start an acquisition, the samples are stored in the on-board memory, and then you will from the host machine at some point "fetch" the data to have it stored on your computer.  Since you can write to on-board memory faster than it can be transfered to the host, more memory means that you can acquire more data before it fills up.  This equates to larger records and/or longer acquisitions.

I hope this makes it more clear.

-Nathan

[meBaga]

OK, Thanks for the reply, I also want to know that, how it is related with "Sample Rate" and "Number of Samples to Acquire" ??

Actually I want to acquire a signal of 1 MHz, @ 50MS/s for a time span of 40 mili Sec. That Means I will be acquiring 20MS. Which one is preferable ?

[Nathan-P · Accepted solution]

Your math isn't quite right.  If you acquire data at a sample rate of 50MS/s, for 40ms, you will actually end up with 200,000 samples (200kS).  If you acquire for 400 ms (0.4 sec), then you are right, and would have 20MS (20,000,000 samples).  

Each sample on the USB-5132 takes 8-bits, or 1-byte of memory.  

So, (200,000 samples) / (1 byte) / (1024 bytes per kB) = ~196 kB.  

or,  (20,000,000 samples) / (1 byte) / (1024 bytes per kB) / (1024 kB per MB) = ~ 19.1MB

So at 20MS, it will use up ~19.1 MB of onboard memory.  Above is the formula for converting number of samples into memory requirements.

I hope this helps.

Nathan