Module speed, FPGA speed, Controller speed and timed loop speed

[K.Waris]

Hello.

I am developing an application to acquire analogue signal at 800kS/s. Budget allocated doesn't seem to be sufficient to buy on over-spec hardware. So have to be very very specific about every component. I had a look on the website and chosen the following hardware.

9221 8 Channel Analogue module capable of sampling at 800kS/s. I am not sure if this sampling rate given in module specification means that it can acquire upto 800kS/s or it is the sampling rate ADC of the device samples at in which case the device might not meet Nyquist criteria and the module capable of sampling at 1.6MS/s is required which I think isn't available?

9012 controller- - 400MHZ controller. If I put a while loop inside a VI under RT target, Does it run at 400MHZ by default provided there is no code inside it? Is so I could certainly use loop time express vi for sampling at the required rate.

What about the timed loop? I have just developed an RT project and added vi under RT target. The timed loop default clock rate is 1kHz and I cant select higher than 1MHz?

9112 chassis. Default clock rate 40MHz. Same question as for 9012 controller above.

Kind Regards

[Pete.Dunc · Accepted solution]

Hi AustinCann

If you need to acquire at 800 kS/s then the the NI-9221 module will be able to do this, if you are only using 1 channel that is.  The module using aggregate sampling, so the maximum rate will be split over the channels you are using.

If however, you need to detect frequencies of >400 kHz then you would need a higher sample rate to detect these, as you have mentioned.

The controller processor will run at 400 MHz although the loops in your code will not run at this rate.  On the real-time target you can use a timed loop to certain clock sources - typically 1 kHz and 1MHz - and define the period in terms of the selected clock.  If you require faster loop rates you can always code directly on the FPGA.  The CompactRIO Developers Guide is a comprensive document and discusses the majority of RT and FPGA concepts.

The best course of action would be to contact your local office, as they have all the resources needed to spec out your system.