Multi Channel Problem

[Tino_1111]

I am a new user to Labview and having some problems. The main issue that seems to be occuring is that when I put multiple input channels (dev1/ai17,dev1/ai18... ) to be recorded to an excel file the number of samples per channel changes as per putting only one single input channel. If I have only one channel selected the program will record temperatures every 0.5seconds, if I put more than 1 the program takes samples every ~10ms. I am trying to have multiple input channels to take 1 sample of each channel every specified frequency (ranging from every .5 sec to 2 sec). I do relize that this code may not be nice to look at but could anyone suggest some ways to conquer the problem?

Labview 8 user.

[Dennis_Knutson]

I'm not sure what you are expecting. You have no code at all to set how often you take a sample from either one or multiple channels.. The rate setting determines the time between multiple samples and you are not taking multiple samples. You are taking a single sample and then the loop starts a new acquisition. The time between loop iterations in your code is indeterminate. With single sample mode, you have now reverted to software timed acquisition. If you can live with some jitter, put a Wait (ms) or Wait Until Next ms Multiple in your loop.

[Wayne.C]

Tino,

LV ships with many excellent example vi's.  Take a look at LV example titled Cont Acq&Graph Voltage - Write Data to File (TDMS).vi. 

[Tino_1111]

Thanks for the reply Dennis and Wayne, I am not sure how an example of the code would look like to set how often to take the sample with multiple channels. The rate setting makes more sense after you have described it to me but when I take multiple samples I usually break the channels in a continous string with commas. I do relize that this is not muliple channels but does creating an 'append true/false string' for multiple channels do the same thing as what I have already? The main issue is that I am not sure what needs to be changed or added to get the simple effect and consistency I need. Thank you for the info.

[Dennis_Knutson · Accepted solution]

For acquiring a single sample from multiple channels at some rate, the code below should be close to what you need. The rest of your requirements I'm not sure I understand and I am also not familiar with the Express VIs that you are using.

[Tino_1111]

Thanks Dennis it helped!