topic Re: how to continously record data in LabVIEW

how to continously record data

Hsin — Thu, 08 Dec 2011 20:32:15 GMT

HELLO

I am trying to cotinously record thermocouple and pressure data. I am only able to capture the final data upon clicking the stop botton. How can I continously collect every data point?

BTW, I am using LabVIEW6 with XP

Thank you

Re: how to continously record data

X. — Thu, 08 Dec 2011 23:36:25 GMT

Did you try to take a look at the DAQ examples (Help>Find Examples...>>Hardware Input and Output>>DaQmx>>Analog Measurements>>Temperature)? I am pretty sure there is one that is doing exactly what you are looking for.

Re: how to continously record data

Hsin — Thu, 08 Dec 2011 23:41:39 GMT

YES! I did.

But the example didn't record the data.

Re: how to continously record data

X. — Thu, 08 Dec 2011 23:55:41 GMT

Sorry, I can't look at your VI (too early a version for me). Which example did you try? What hardware are you using? Do you get an error and if yes, which? Did you try to test your hardware from within MAX first?

Re: how to continously record data

Hsin — Fri, 09 Dec 2011 00:10:02 GMT

I use the "continous thermocouple mesurement", but I think because of the version, your might different.

I am using 6023E with SCXI devices. They're recognized by MAX.

I didn't get any error, just couldn't record each of data point, only the point when I click the stop.

Re: how to continously record data

Hsin — Fri, 09 Dec 2011 00:42:58 GMT

Please see my program which is attched. Thank you

And I have a loop for overall as well.

Re: how to continously record data

X. — Fri, 09 Dec 2011 00:43:40 GMT

Here is what I can see of your code, so it is in part guess work:

Re: how to continously record data

X. — Fri, 09 Dec 2011 00:55:26 GMT

So in essence, your code should do what you are describing it does. It is a wonderful example of beginner's code (we have all made some similar stuff at the beginning of our wiring attempts!).

Unless you really want to look for a loooong while at each bunch of thermocoupe data before moving on to the following, your code should look something like that (in your beginner's style, no offense intended, but there are a few new concepts in the newer versions of LV that would call for an entirely different structure):

This is obviously oversimplified, but that should give you an idea.

Re: how to continously record data

Hsin — Fri, 09 Dec 2011 01:03:20 GMT

Wow! That's fantastic! Thank you so much!

I will try to re-build my program.

If I have more problems, can I ask you again?

Re: how to continuously record data

Hsin — Fri, 09 Dec 2011 15:57:01 GMT

Dear X,

I got the data continuously! Thanks a lot!

But I have another question is the data is repeatedly record on 1 second.

EX: 12/9/11 10:55:01, 27E+030E-150E-3, 27E+030E-150E-3, 27E+030E-150E-3, 27E+030E-150E-3, 27E+030E-150E-3

Should I set anything for only record a set of data for a second?

Re: how to continuously record data

NIquist — Fri, 09 Dec 2011 16:05:40 GMT

If you want to collect every second just change the delay time (VI with the little clock) from 10 to 1000. It's in milli-seconds so 1000mSec = 1 Sec.

Re: how to continuously record data

Hsin — Fri, 09 Dec 2011 16:12:45 GMT

I did use the delay time for 1000!

But the data still shows like

12/9/11 10:55:01, 27E+030E-150E-3, 27E+030E-150E-3, 27E+030E-150E-3, 27E+030E-150E-3, 27E+030E-150E-3

12/9/11 10:55:02, 29E+039E-159E-3, 29E+039E-159E-3, 29E+039E-159E-3,29E+039E-159E-3, 29E+039E-159E-3

I did like to have data looks like

12/9/11 10:55:01, 27E+030E-150E-3

not repeat for each second

Thank you

Re: how to continuously record data

X. — Fri, 09 Dec 2011 18:02:10 GMT

I don't understand what you are trying to achieve.

1) Do you want to display the time of acquisition with better precision that one second?

2) Do you want to acquire at a specific rate?

In case you want to achieve 1, I would recommend saving raw "tick" values (ms since an arbitrary time t_0) (converted to a string) rather than the date/time string provided by this:

In case you want to achieve 2, the architecture of your program should be slightly different from the one I showed before. You probably want to set the hardware acquisition rate of your waveform data beforehand and use an acquisition mode that buffers the recorded data internally (that is in a RAM buffer) and use a VI that asynchronously polls your hardware to get all the available data. It's difficult to provide you with a definite answer without having access to your code (not your fault though).

The architecture of your original program (and that I showed) does not provide very precise acquisition rate, as it is dependent on the willingness of your PC to adhere to the "Wait" function delay. That effectively never happens...

Let me know whether this makes sense.

Re: how to continuously record data

Hsin — Sun, 11 Dec 2011 20:54:37 GMT

Thank you!

I think I got what I need!