How can I output a constant on an analog channel？

[Ian Colman]

Hi,

Is it okay if you clarify your question please? At the moment you aIre writing your data to an LVM file using a write to LVM express VI. Do you wish to do this using lower level VIs to speed up execution time, or are you talking about your DAQ speeds?

Thanks,

Ian

[foolooo]

At the moment I wanna use the output channel to generate signals (of any type) continuously, and use the input channel to acquire them. I wanna test how quick this process (especially the input) can be. So I set both the channels run at hardware timed single point. From the files generated I can see that the reading rate is too small, so is there any method that I can speed up the process? I tried setting the sample clock of the analog input at different frequncy, but it was still not quick enough. From the specification I saw that the input rate could about 1.25M S/s, but what i've got was much smaller.

Thank you.

[Ian Colman]

Hi,

Okay what you need to do is set up your tasks for continuous generation/acquisition, then make sure you acquisition loop only contains the read or write VIs in order to obtain maximum speed. If you put a write to file express VI inside this loop, your rates will be allot slower.

Let me know how you get on,

Ian

[foolooo]

Hi, Ian

Thank you for your reply, and I need to record the data so as to process it in my further project. I updated my file. When the process run 100,000 times, the data stored in the buffer will be written into a file. But the writting process takes about 750 ms every 100k size. And can I get rid of the lag? Because when it is writting, the process in the For Loop cannot run. (I was thinking about using another buffer to shorten the writting period, but I'm not sure the exact programme.) Thank you.

[Ian Colman]

Hi,

I have tidyed up your code a bit and redone your error clusters to force correct execution but I don't think that this will have any great effect on the execution time of your file handling. Saving to file will take a few miliseconds, I don't think that you will be able to save to file much faster than you are at the moment.

Regards,

Ian

[foolooo]

Hi,

I don't think the "writing" process could be quicker. But can I continue doing the output and the input while it is writing the data into a file? So that the programme can work continuously without a wait.

Cheers,

Bo

[GovBob]

Have you looked into the producer consumer design pattern with a queue. The acquisition loop would be the producer and you would write your LVM files in the consumer. Just my 2 cents hope it helps.

[foolooo]

It works! Thank you for your suggestion. And I really learnt much from it. Thank you all.

Bo