Loop test on M-series card

[Poormanphysics]

Hello to readers:

I wrote a simple loop test code using Express VIs for testing a new M-series card the lab recently acquired. The test code simply uses the two ao0 and ao1 output channels into two analog inputs ai7 and ai8 (see attached GIFs) it took me sometime to figure out the meaning of multiple errors I get when actually choosing the available choices of sample output update method to work. I seek answers to why only a " a single point update" is the only one that works for these scheme? For the case of N-updates, Continuous and Hardware timed schemes prompts multiple errors?

Regards,

Berns B.

[Lorne H.]

Dr. Berns,

I do not believe your GIF were attached to the previous post.

With that said, you should be able to do analog input and output at the same time on your Data Acquisition (DAQ) board without any problems.

Could you tell me what DAQ board you are using?
Which error codes are you recieving?

Also, it might be easier for me to tell you what is going wrong if you posted your test code.

Something to check for...
You cannot have two seperate Express VIs for each analog input.  Likewise, you cannot have two seperate Express VIs for each analog output.  If you want to use two analog inputs you have to access them through the same express VI by selected one or more analog input (or output) lines from the channel select dialog box (when setting up the DAQ Assistant.).  Do not misunderstand me, you will need two Express VIs.  One for analog output and one for analog input.

Check out the knowledgebase below...
Why Do I Get Error -50103 When Using Multiple DAQ Assistant Express VIs?
This might give you some insight into some of the problems you are having.

I hope this helps, continue to post with more questions so I can completely solve your problem.

Lorne Hengst
Application Engineer
National Instruments

[Poormanphysics]

Hello:

Here are the attachements. By some chance I was not able to check them. I like to patch the older code in DAQ Legacy implemented VIs with newer Express VIs but i have some weird behavior I observe. For example the Select Signals Express VI has only seven (7) signals you can choose if I have 14 Analog Inputs from my M-series Card a PCI6251 how is it possible for me to read and graph the rest? Can you have multiple DAQ assistant Express VIs?

This is all for now.

Thanks,

Berns B.

[Poormanphysics]

Hello again:

Here is my attempt to separate the "position feedback" signals from "faults feedback". I can't figure out how is it possible for 14 analog signals to be decoded or demultiplexed by a Signal Select Express VI which only has seven select options?

Regards,

Berns B.

[Poormanphysics]

Hello again:

You mentioned in the last thread that I cannot have two Analog Output Express VIs that is true if somewhow the lie flat together on the same block diagram. In the attached example here I attempted to make two independent knob control of output voltage for my XY Servo drives which are independently controlled but is contained in one and the same VI. How is this possible? Does  not mean this would also be true for analog inputs?

Regards,

Berns B.

[Lorne H.]

Dr. Berns,

I have some answers for you...

"Can you ahve Multiple DAQ Assistant VIs?"

Yes and No.  You can have as many as you want as long as they do not confict with each other.

What causes a conflict?  Having two different DAQ Assitants accessing the same Analog Input or Analog Output on the same board at the same time.  Your most recent program avoids this when doing the Analog Output by making sure the DAQ Assistants do not run at the same time and by not having the DAQ Assistant do continuous task timing.

"Why can I only see 8 signals in the Select Signals Express VI when I want to see all 16?"

There is a Knowledge Base which partially answer this question...

Will the Select Signal Express VI Work With More Than 8 Signals?

The solution in the knowledge base will only work for finite and continuous DAQ Assistant tasks and not single point.

"How is this possible? Does  not mean this would also be true for analog inputs?"

What you did in the VI you sent will work.  There is another option though.  You could group the knob controls together in an array and connect them to the input of one DAQ Assistant which writes to both analog output ports at the same time.  Using one DAQ Assistant as opposed to two is cleaner programming in my opinion.

It looks like you are on the right track.  Down the road you might want to look into using the lower level DAQmx VIs as opposed to the DAQ Assistant to accomplish your task.  The lower level VIs will give you a little bit more flexibility.

I hope this helps,

Lorne Hengst
Application Engineer
National Instruments