Newbie: Data acq. with NI 9081

[1984]

Hi there,

I have found the following code on one of our stands. The stand uses an NI 9081 with several modules. All the data acquisition is in the RT part of the controller (so the FPGA is not really used as I would imagine should be used). It seems we grab a sample from each channel, merge them into an array and then send it to the host computer.

The concerns I have is this:

1, it seems the sampling rate peaks aroung 1kS/s with this solution

2, I assume all the channels are sampled one by one, and not simultaneously (which ends up a syncing issue)

3, now we sample about 10 channels or so, but what if we have 100? The code would look really ugly.

I am not an RT expert at all, moreover right now I dont even have the RT toolkit installed on my computer. But I would imagine that as with DAQmx we should be able to get multiple samples (speeding up the measurement) from each channel AND we should be able to merge the sampling into one task, so we can get rid of the syncing problems.

I fully understand that the data acq. should run on the FPGA to utilize the tool properly, although we wont be able to move to this direction in the next couple months due to workload issues, so I rather want to upgrade the RT code for now.

Can you advise what would be the proper way to achive a better performance?

A screenshot would be great. Do we have a suitable example included in the example finder? 

I appreciate any help!

[Esteban.R]

Hi 1984

0-      The FGPA is actually been used but is configured automatically take a look to this document.

The RIO Scan Interface Under the Hood

1-      The maximum rate at which LabVIEW RT can update the I/O variable is 1kHz. Take a look to the section 1 of this document.

“Using NI CompactRIO Scan Mode with NI LabVIEW Software

“Using NI CompactRIO Scan Mode with NI LabVIEW Software……..The NI Scan Engine, a component of LabVIE...

2-      This will depend on the sampling of each module, in other if the module allows simultaneous sampling or not. In order to check this you check the specification tab of each modulo in the NI website or the manual.

3-      Keep in mind that the code in the block diagram it is recommended to fit your screen so that you can see everything, is a recommendation not a rule. In order to do this you will need to create subVIs, for example take a look to this document and image that I have attached.

Tutorial: SubVIs

4-      I am not sure what exactly do you mean, but if you want to get an array instead of a single point this cannot be done on scan interface you will have to use the FGPA interface in order to do that.

5-      What exactly do you mean with better performance? Have a higher sampling rate? Reduce the execution of the deterministic loop? Analyze data? Etc

6-      The NI example finder has plenty of examples for each module; some modules have examples in scan interface and FPGA interface.

7-      If you are new the RT, FPGA and you will also like to optimize your code keep in mind that NI has courses for those topics.

NI courses

I have respond most of your questions in this thread or forum but keep in mind that in order for other people to find answers to their question that might be similar is easier to handle one issue or question per forum post

Regards

Esteban R.