global virtual channels sampling rate

[Bertha]

Hello, does anybody know the sampling rate of a global virtual channel created in max tied to an RT system(remote)? I assume that is 1 sample on demand. If so, is it possible to change it? or do you have to create a task to be able to change them? I am using datasocket and shared variables to access the global channel in my PXI chassis and I don't want a program running on the RT. I will appreciate any input or way around it. Thanks

[Jim_S]

Hello Bertha,

After reading your post, I have a few questions to ask you about it. It looks like you want to setup a task on you host machine that will bypass the Real-Time system and acquire data from the cards in your PXI chassis. Unfortunately, this can't be done. You will have to setup a program that runs on the Real-Time system that acquires the data and sends it back to the host machine.

If you don't want to do this, you can remove the PXI controller and connect it to your computer via a MXI cable which would make the PXI chassis a continuation of your motherboard.

I hope this information helps you.

[Bertha]

Thank you for the response, I kind of knew this but I wanted to confirm. I haven't tested it and I have seen that you cannot do it in max but is there a way to have them both running at the same time on the same channel? a global virtual channel and a task on the RT?

[Jim_S]

Hello Bertha,

After reading your post, I wasn't clear what your question is. Is the global virtual channel going to be on the RT target or your host machine? If the global virtual channel is going to be on the target with the DAQmx task, do you want to have a global virtual channel and a DAQmx task to access the same channel on the Real-Time target at the same time? This isn't possible because the resource will be reserved for either the running virtual channel or the task.

If this doesn't your question, could you provide more detail about this? 

[Ben]

Hi Jim,

RDA - Remote Data Acquisition used to be able to acquire from hardware on another machine on the same LAN.

That sounds like a perfect fit for this question.

If not currently supported what was the last version that did support RDA?

Ben

[Jim_S]

Hello Ben,

From my research, we have moved away from using this in DAQmx as of 8.0. During my research about this, I did find a way to possibly do this using DAQmx OPC. The DAQmx OPC server will allow you to pass the reference to the device through a shared variable. From reading this KnowledgeBase though, I am not sure if you can do this to a Real-Time target but it is worth a try. From what I tested with this, it could be possible but from everyone I have talked to, not many had tried this. There is also a DeveloperZone on this as well that goes into some more detail about this as well.