topic Re: daq and write to array in LabVIEW

daq and write to array

ballbouncing — Thu, 08 Mar 2012 14:09:03 GMT

Hello All,

I have a data acquisition task, as shown in the attached file. In order to speed up the data acquisition process, I am planning to first acquire and save the data into an array, and then write the whole chunk into a txt file. I have searched a lot, but I could not find how to do this. Can someone instruct me or give an example link to do so.

Thanks.

Amir

Re: daq and write to array

Phanuel — Thu, 08 Mar 2012 14:37:04 GMT

Hi Amir,

I found de following example for you:

Continuously Read Data and Log to a TDMS File

https://decibel.ni.com/content/docs/DOC-11300

This example acquire data and write after the acquisition the data in a TDMS File.

I think this example will help you.

Re: daq and write to array

ballbouncing — Thu, 08 Mar 2012 15:24:04 GMT

Thank you very much for you help. But I have two more questions:

1- The TDMS file, as pops up at the end, does not have the corresponding time stamps for each acquired voltage value. How can I store the time stamps in the same file as well?

2- I have another dependent measure in the loop that I need to store it in the same file. How can I add this value to the TDMS file so that at the end I can have that as well.

Basically I need three colums in my output TDMS file:

1- Voltage values

2- The time stamps correponding to each acquired voltage

3- Another dependent measure, which is computed within the loop

Thanks.

Amir

Re: daq and write to array

Xenox — Thu, 08 Mar 2012 15:36:30 GMT

Hi Amir,

with the TDMS Write.vi you can add Channels and Groups to your TDMS File.

The following example write random values in specific groups and channels.

Timestamping Queued Data and Storing in TDMS Files:

https://decibel.ni.com/content/docs/DOC-5789

Re: daq and write to array

ballbouncing — Thu, 08 Mar 2012 17:41:38 GMT

Hi Again,

I have cutomized the example for my application. Attached you can find my code. But there is still a problem. At the end of the trial, as set by the total time (sec), the TDMS file does not show all the values, i.e. it is too short. Where are the other values? I thought I saves all data points!

Additionally all the measurements are 0. I have connected it to the clock source but they are all still zero.

Thank you for your help.

Amir

Re: daq and write to array

Bijay — Fri, 09 Mar 2012 08:50:50 GMT

Hi Amir,

Remove that 100ms wait vi from 2nd loop and connect 100ms to timeout terminal of dequeue element.

I hope that will work.

Regards,

Bijay

Re: daq and write to array

Xenox — Fri, 09 Mar 2012 08:59:50 GMT

Hey,

at first please allow debugging in your VI. With debugging you can set probes, which help you understand the function of your VI:

http://digital.ni.com/public.nsf/allkb/22729F1BAC6BBDD086256FDC005FE8FD

What clock source do you connect to your Dev1/ctr1? Did you check your clock with a scope?

(Dev1/ctr1 is not the internal clock!)

I did some changes in your VI:

Xenox

Re: daq and write to array

Bijay — Fri, 09 Mar 2012 09:06:45 GMT

Hi xenox,

Try this....

Go to VI properties > category Execution >check Allow debugging.

Continue with work.

Regards,

Bijay

Re: daq and write to array

Xenox — Fri, 09 Mar 2012 09:10:41 GMT

Hi Bijay,

i know

have a look at my link I posted before:

http://digital.ni.com/public.nsf/allkb/22729F1BAC6BBDD086256FDC005FE8FD

Re: daq and write to array

ballbouncing — Wed, 14 Mar 2012 21:44:48 GMT

Hi Bijay,

and thanks for your response. Unfortunately I could not open your example code, since it is written in a higher labview version as mine, which is 8.6. Can you help me with an example that the queue is filled in two different loops. In the example above, all values are stored in a single loop. What if I want to store x value from loop 1 and also store y value from loop 2. can I add them to the same queue? or I have to use another queue?

Thanks.

Amir

Re: daq and write to array

Ryan-C — Thu, 15 Mar 2012 17:16:59 GMT

Hi there,

You can most certainly add data from different loops to the same queue. There is a simple Example VI in the NI Example Finder called "Queue Multiplexer.vi".

I'm not sure if it's in the LabVIEW 8.6 Example Finder, so I saved as previosu version for you and attached it.

Best of luck!

Re: daq and write to array

shahjenil — Fri, 22 Mar 2024 07:20:48 GMT

This Link is no more available I am trying to resolve the same problem can you share an example?

Re: daq and write to array

Bob_Schor — Fri, 22 Mar 2024 12:45:23 GMT

Please do not ask for "Me, too!" help on a topic that has been idle for more than a decade. If you need help with your problem, press the "Start a Topic" button and clearly explain your problem/question. It is best if you include your attempts. Attaching your LabVIEW code is preferred to attaching a "picture of a VI", but many of the more-experienced Forum users are running LabVIEW 2019 or 2021 (I'm one of them), and won't be able to open LabVIEW 2023 or 2024 code unless you "Save for Previous Version" (on the "File" menu).

Bob Schor

Re: daq and write to array

shahjenil — Fri, 22 Mar 2024 13:41:19 GMT

Actually I am not working with LabVIEW, currently I am using the ni daqmx library in python but was facing similar daq issues, didn’t knew if it was worth starting as a new topic on a LabVIEW forum if it is then I’ll be happy to start a new discussion where I can share my files too.

Re: daq and write to array

Bob_Schor — Sun, 24 Mar 2024 23:26:00 GMT

The LabVIEW Forums are an excellent place to ask for help with LabVIEW issues. If you are mainly using DAQmx in a Python environment, bypassing LabVIEW, you might want to ask in some Python forums ...

Bob Schor

Re: daq and write to array

mcduff — Mon, 25 Mar 2024 00:41:17 GMT

Use the built in logging features of DAQmx, data will be saved to a TDMS file. Python has an excellent, if not better, TDMS library that you can use to read the files or convert to another format.

you can post some of your python code here as the functions are similarly named.

Re: daq and write to array

shahjenil — Tue, 26 Mar 2024 13:45:05 GMT

Hey,

So I have attached the Python file that I am using currently to scan a 2d grid using a confocal microscope and DAQ, this program stores the result in the 2d matrix 'pmt_data' and gives me the desired output(image of the scan) however the program takes 30-40 minutes for just 200 pixels by 200 pixels grid, how do I optimize it? am I doing something wrong while writing and reading the data?

Re: daq and write to array

mcduff — Tue, 26 Mar 2024 14:45:44 GMT

Nothing looks overtly incorrect in your python script.

How fast do you want this to go? 200 x 200 pixels is 40000 pixels. 40 minutes is 1000 pixels per minute.

Re: daq and write to array

shahjenil — Tue, 26 Mar 2024 15:20:42 GMT

When I am using the ScanImage software through MATLAB if you are familiar with it, I am getting more pixels scanned in a matter of seconds which is why I was wondering if can get a similar run time in Python or LabVIEW using NI-DAQmx.

Re: daq and write to array

mcduff — Tue, 26 Mar 2024 15:36:30 GMT

@shahjenil wrote:

When I am using the ScanImage software through MATLAB if you are familiar with it, I am getting more pixels scanned in a matter of seconds which is why I was wondering if can get a similar run time in Python or LabVIEW using NI-DAQmx.

I am not familiar with ScanImage software. A long time ago, I was doing z-slices of florescent images and this is the basic algorithm,

Move to Position
Check if in Position, if false wait
Take wide field Image
Repeat

For your case, you have

Move to position.
Check if in position
Readout PMT, Start Daq, stop Daq, Average values, etc

To speed this up adds possible programming complexity and bugs

Start DAQ and continuously acquire Data
Move to Position
Check if in position
Query DAQ for latest values now that you are in position. No need to start, stop daq, etc. That will save some time at the cost of programming complexity.

Does ScanImage take a single point at each pixel, multiple points, does it take data while the objective continuously moves and interpolates pixel positions? All of these things can speed up acquisition time at the cost of complexity of your program.

In your python script I see a simple raster scan that is easy to program, understand, and relatively bullet proof. It's cost is a long acquisition time.