DAQ program randomly hangs for 1-2 seconds

[alauber]

HI!

I have a problem with the data acquisition program I made. Here is the situation:

- We have an CompactDAQ data acquisition hardware.

- We use labview DAQmx

- The data are acquired with a rate of 1 Hz, during 24 h

- The data to acquire are: 

• about 20 Analog signals
• 1 digital signal
• 2 Frequency signals

- two of the Analog signals are used to control a ventilator

- the rest of the signals have to be monitored, that is they have to be plotted on a graph.

My program works well for hours, but for a reason I don't understand, sometimes the program hangs for 1 to 2 seconds randomly. That means that the data buffer is filling. This situation can cause major problems, as I'm using the acquired data to control a ventilator. So my questions are:

-  has someone an idea why the program can hang for 1 or 2 seconds? It seems to be a Windows XP problem, as the loop I use for data acquisition in labview only needs 0,2 seconds to complete, so there is actually plenty of time left for other actions.

- Is there a possibility with DAQmx to clear the data buffer, or at least to read only the last values?

Thank you for you help!

Marc

[Marian_O]

Hello Marc,

thank you for posting at the National Instruments Forum. I would like to help you, but I have a few questions to encircle the problem:

a) Is the CompactDAQ (cDAQ) Hardware connected to your computer directly or are you using some kind of USB-Hub? If so, please connect the cDAQ directly to the computer.

b) How did you configure the DAQmx Triggering/Sampling? Is it continuous, N-samples or 1-sample?

c) How do you find out, that the system is "hanging" for 1 to 2 seconds?

Best regards

MarianMO

[alauber]

Hello MarianMo,

Thank you for your help! Here is the reply to your questions:

a) Yes, the cDAQ is connected directly to the computer

b) I initialize a DAQmx continuous task outside of the loop, and in the loop I acquire the data, one sample at the time. The user can stop the program with a mouse click, and then the task is closed outside of the loop. I am using a timed loop right now, but I also tried with a standard loop.

c) I noticed that the system hangs first because the ventilator I control via my program started to swing. Then I used the feature of the timed loop to determine exactly when, and how long the loop hangs. I haven't found any clue yet, and it seems to happen randomly. I have programmed the timed loop to execute every second. When using the features of the timed loop, I see that the loop only takes 0.2 seconds to execute, apart from the time when it hangs...

So far, I have tried to restart the task when the timed loop detects a problem, in order to clear the buffer. But that takes quite a lot of time and didn't solve my problem.

I hop I answered your questions!

Best regards,

Marc

[Marian_O]

Hi,

so are you stopping the timed loop, when it runs late? Is it possible, that you post your code here?