LabVIEW data acquisition Setup Multifunction DAQ

I have doubts as to the acquisition of data in the LabView environment. I used the block diagram (Figure 1) below to review the update of the readings for the execution of a loop.

Block 1 has been used to enable a task (first steps) with 3 channels (al) analog input AI3 and even set up the channel. In this case, the data bus (data-block 4) are construindos by 4 columns of data (provided by task 3 AI3 more).

Block 2 is used to set the sampling rate in this case is 1 Hz (1 sample per channel x 1 rate).

In this case, it worked as I expected (Figure 2). This allows to conclude that the interval between each sample was 1 second. The saw took a second in the iteration.

The second step was to change the amount of data sampled in accordance with Figure 3 channels in block 3.

Now, each channel showed 10 samples, while there are 4 channels configured, we have 40 samples. In this case the iteration totalled 10seconds (point to 1 Hz and 10 samples per channel-figure 4).

The first question is what is the time between each sample obtained by channel?

In this type of configuration (multiple channels), block 3 provides 10 samples in each channel, as well as the sampling is done, IE, the block gets 3 10 samples from a channel and passes to the next channel or gets 1 comp each channel and repeat this process up to 10 samples per channel?

What is the best way to make sure that the interval between each sample is constant?

If anyone knows any text that explains what the function blocks of data acquisition information please.

Thank you

Gabriel

Well, there are several ways to read the signals of multiple signals, and each of them has different behavior. I couldn't see how you get mutiple channels, because in the two codes, you set a channel in your codes. Take a look at this figure:

Here you can see how to set multiple channels using DAQmx, using commas to separate the channels. About the ways different ways that you can read the signals, you can look at the links I sent in my first post to learn more about them.

In a few words, the time between samples from the same channel is T = 1/Fs, corresponding to the sampling frequency Fs. It is not a rule to determine the interval between samples from different channels, because it will depend on how you did your code, and as I sad, there are different ways to do. You can acquire the samples at the same time, or you can configure your code to read a fixed number of points of a channel and then read another fixed number of samples to another channel (https://decibel.ni.com/content/docs/DOC-28279). You can acquire a finite number of points, or you can acquire all the time. Yet once, take a look at the material that I have already sent. It will help you find the best solution to achieve your code according to your application.

Kind regards

Pedro

Tags: NI Hardware

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