Aggregate Sampling Rate

[AdamLeicester]

Hi,

I'm looking at possible solutions for data aquisition. I'm going to be using 4 or 5 analogue inputs and a couple digital inputs. For the analogue inputs most of them won't need a hugely quick sampling rate except for one which needs at least 100ks/s. I've noticed all the most cost-effective solutions have an overall sampling rate (eg. 250ks/s) which is spread over all channels. For these products, such as the NI-9205 compactRIO module, is it possible to distribute the available sampling rate unevenly between channels (ie. could I assign 100ks/s to one channel and spread the remaining 150ks/s between the remaining channels in use)? Thanks in advance for any help,

Adam

[DanVickers · Accepted solution]

Hello Adam,

To answer your question about sharing sampling rate, it is not possible to have different sample rates on one module, as this KB describes: Here (http://forums.ni.com/t5/Multifunction-DAQ/Aggregate-sampling-rate-and-Multichannel-Scanning-Rate/td-....

In the case of the 9205 this module multiplexes between all the channels (32 if set up in single ended mode or 16 in differential) this means the sample rate of 250KS/s is the total across all channels.

If using differential mode then the samples per second on each channel will be 250KS/s divided by 16, ie 15KS/s. However if you are to only specify 4 channels then the max sample rate will be 250KS/s divided by 4, ie 62.5 KS/s.

One way to get round this would be to use 2 x 9205 in one of our newer CompactDAQ chassis, which has 3 AI timing engines. This allows you to set different timings across 3 different modules. This is described well in this KB: Here   (http://digital.ni.com/public.nsf/allkb/E7036C1870F6605686257528007F7A72)

I am sorry this reply has taken so long, and I hope the information above helps.

Please feel free to reply with any further questions.

If you would like I could get one of our Technical Sales Engineers to give you a call to discuss a data acquisition system with you further?

Kind Regards