Write to Measurement and Write to Text File

[Alexis_Koul]

Hello,

When I am connecting directly the output data from my  DAQ to Write to Measurement, the data are saved in the same frequency as I have input in the DAQ (1KHz). But when I am trying to save the data to a Write to Text File, the data are saved on much lower frequency (10 Hz).

Thank you. Any feedback is appreciated. 

Regards,
Alex

[pincpanter]

Writing to a text file is notoriously much less efficient, although 10 Hz only is a very poor performance, assuming you are writing on your local disk.

Probably you are opening and closing the text file at each write operation, instead it should be opened/closed only once.

Post your code (vi or snippet) for more suggestions.

[GerdW]

Hi Alexis,

it seems there is a problem in your VI.

As you forgot to attach that VI you need to debug on your own!

[Alexis_Koul]

Hello Paolo,

Thank you for your reply. Please find attached a screenshot of that part of the VI. The parameter e is from another loop, but even if I take it out, still I have the same issue. 

Thank you again!

[Alexis_Koul]

Hello GerdW,

I attached a screenshot of my VI in my previous reply. Any feedback is more than welcome. Thank you again!

-Alex

[RavensFan]

Screenshot of VI <> VI.

The problem might be in the way the Express VI is setup.  But we can't see that in a picture.

[GerdW]

Hi Alexis,

---

@Alexis_Koul wrote:

I attached a screenshot of my VI in my previous reply. Any feedback is more than welcome.

---

Feedback:

I asked for VI(s), but you refused and only attached an image…

I see too many local variables in this tiny image.

[Alexis_Koul]

Hello,

In the DAQ assistant, I have Acquisition Mode: Continues Samples, Samples to Read: 100 and Rate: 1 KHZ

So in the Write to Measurement file this gives me data every 0.001 seconds. So 1000 data points per second..which is want I want

In the Write to Text file I am getting every 0.1 seconds

If I change the Samples to Read, for example 10, I am getting data almost every 0.01 or 0.009/0.008 seconds...the value is not constant

The local variable e is a result of a calculation from the other while loop. In the other while loop I am using Visa Serial to control Arduino

Again, thank you!

[pincpanter]

Reading 100 values sampled at 1 kHz takes... 0.1 seconds.

At each loop iteration, the DAQ assistant node outputs 100 values (per input). Your code extracts the first of those values and saves it into the file. As a result, you are storing values at 0.1 Hz and trashing 99% of the samples.

To solve this problem, insert a For Loop and save all elements in the three arrays of doubles.

Test if the file writing can keep up with the acquisition timing. If not, you need to separate acquisition and writing in two different loops.

[Alexis_Koul]

Hello Paolo,

Thank you very much for your reply. What I did now was to just add a For Loop in the part of the VI that I am saving the data and I put as N = 100.

It looks that it works good, and I am getting almost 1000 data points per second, is just that many values are repeated. So the time stays the same and measurement is repeated.

I am not sure what you meant with to add three arrays of doubles, since I already put every data different Index Array and then to the Concatenate String.