Mixed Sampling Rates - Error 1073807339 with USB 9215

[GigaMilp]

Hello

I've been using a four channel NI cRIO-9215 with a USB-9161 carrier with success for some time now. Normally I use the 'analog 2D DBL N chan N samp' VI and strip off each channel with an array index. The sampling rate is the same for each channel. (Physical channels = Dev1/ai0:3)

I want to sample two channel at different rates. ie see attached diagram... (e.g Physical channels = Dev1/ai0   and  Dev1/ai1)

When running this program the scales autoadjust for both graphs followed by Error 1073807339. On continuing a further Error 200284 is displayed.

Question: Can this H/W with some VI, acquire data from more than one channel at different sampling rates? i.e one channel may be 1000hz and the other 50hz

I don't want to sample all channels at the highest frequency, and then display a percentage of the lower freq channel. I would like to display both graphs at their respective acquisition rates.

Has anyone tried this?

Thanks in advance for any advice

Regards

Adrian

[MarkLe]

Hi Adrian,

The normal way to do this is to sample all channels at the highest rate, then divide down (or discard samples of) the data to generate the waveforms for the lower rates.

There is an article on the NI website on how to achieve this here:

http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=BCB8746152612330E034080020E74861&p_...

(this is written for the E series devices, but is equally applicable to the cRIO modules, or any other device which uses DAQmx).

Unfortunatley, you won't be able to define several analogue input tasks with different sampling frequencies, as there is generally only one sample clock available. This is why several analogue inputs are normally grouped together as a task, with shared timing characteristics.

I hope this helps you.

Best wishes,

Mark

Applications Engineer

National Instruments