NI cDAQ-9178 problem

[LievenD]

Dear All,

I am using the NI cDAQ 9178 and seem to have a problem with the unit.  I had some issue's with reading several inputs on the device and pulled out all the cards except one.  I used the DAQ assistant and setup a simple voltage reading input.  When I dictate my loop to run at 50 ms then the last iteration duration shows something around 70.  Even when I increase the loop rate to 200 ms, it still shows around 70.  I am starting to suspect something is wrong with the hardware.

I used the daq assistant and asked for single channel, single point.  In doing so I thought the loop rate would dictate my sample timing. 

Does anybody know what could be the problem or has anybody seen this problem before?

I have added a screenshot of my problem.

Thank you.

Lieven

[LievenD]

I think I might have found the problem.  From playing around with the unit I found I can acquire 100 samples at 1 seconds interval.  But I cannot acquire 1 sample every 10 miliseconds.  From what I can see the unit only does fast data acquisition in the unit itself but it doesn't have the capability of streaming it real time to Labview.

I think I'll have to restructure my software to get it working.  Probably producer-consumer loops or something like this.

However I would still appreciate it if somebody can confirm my suspicion.

Thanks & regards,

Lieven

[alcava.cr]

Hi Lieven,

What you are seeing is that the code inside the timed loop takes around 70 ms to complete the execution. The chassis only provides communication with the module, which is the component that limits the speed of acquisition. I would encourage you to check the specs of your module to clear all doubts regarding your limitations.

Plus, remember that the timed loop structure ensures execution control and is normally used with Real-Time applications. Be careful, Windows is a multipurpose OS so the code inside this loop may not behave the way you want, I recommend using regular loops. And yes, best programming practices such as producer/consumer architecture always helps when it comes to performance.

I hope this helps