NIDAQ continuous and background acquisition

Hello everybody,

I'm trying to acquire and store data from a CompactDAQ from National Instruments. The configuration of the device itselt and the visualization of the data is pretty straightforward, but I'm having trouble in store this data in a matrix that I will be able to access after the acquisition is over.

I'm connecting the device as follows:

s=daq.createSession('ni');
s.addAnalogInputChannel('cDAQ1Mod2', 0, 'voltage');
s.Rate=2000;
s.DurationInSeconds = 60;

to plot the data in real time I use the following lines of code:

lh = s.addlistener('DataAvailable', @plotData); 
function plotData(src,event)
     plot(event.TimeStamps, event.Data)
end

and then I start it in background (I need to acquire data in background in order to perform other tasks at the same time):

s.startBackground();

This seems to work fine for the real time problem, but I'm having trouble to define a callback function that will store all data acquired into a matrix or structure. I'm sure that this is a quite basic problem.

I want to thank you all in advance for your time.

[avinash pabbireddy]

Function definitions are not permitted in this context. i'm getting this error while running the code s=daq.createSession('ni'); s.addAnalogInputChannel('cDAQ2Mod1', 0, 'voltage'); s.addAnalogInputChannel('cDAQ2Mod1', 1, 'voltage');

s.Rate=2000; s.DurationInSeconds = 60; lh = s.addlistener('DataAvailable', @plotData); function plotData(src,event) plot(event.TimeStamps, event.Data) end

[Walter Roberson]

You need to name the file nidaq6258.m, and the first line of the file must be

function nidaq6258

[Jacob Graham]

Hey Everyone,

Looks like I'm a few years late to the party. These solutions and comments have been very helpful, but I still have a problem. The while(~s.IsDone) loop doesn't appear to be working for me. When I run the code below, Matlab remains busy indefinitely while it's on the while(~s.IsDone) line. When I debug and step past it manually, the code that follows works. I'd like to use the command window while the session is running in the background which is why this is a problem.

Thanks for your help

J

function acquireData
  clear global;
  global data
  s = daq.createSession('ni');
  ch3 = addAnalogInputChannel(s,'cDAQ1Mod1', 'ai3', 'RTD');
  ch3.RTDType = 'Pt3851';
  ch3.RTDConfiguration = 'ThreeWire';
  ch3.R0 = 100;
  s.Rate = 100;
  duration = input('Duration of Sampling Period?');
  s.DurationInSeconds = duration;
  time = (0.01:0.01:duration);
  lh = s.addlistener('DataAvailable', @plotData);
  startBackground(s);
  while(~s.IsDone)
  end
  close(gcf);
  plot(time,data);
  delete(lh);
  end

function plotData(src, event)
    global tempData;
    global data
    if(isempty(tempData))
    tempData = [];
    end
    plot(event.TimeStamps, event.Data)
    tempData = [tempData;event.Data];
    data = tempData;
    end

[Walter Roberson]

See the change suggested at https://www.mathworks.com/matlabcentral/answers/6258-nidaq-continuous-and-background-acquisition#answer_24925

Or put in a brief pause() in the while loop so that there is an opportunity for background code to run and events to be processed.

Answer 1

[Chirag Gupta]

Hi Nuno,

There are number of ways to achieve this:

1) Use some global data

function acquireData
global data
s = daq.createSession('ni');
s.addAnalogInputChannel('cDAQ1Mod1',0,'voltage')
s.Rate = 2000
s.DurationInSeconds = 5
lh = s.addlistener('DataAvailable',@plotData);
s.startBackground();
% Do something
while(~s.IsDone)
end

close(gcf);
plot(data); %  plot global data

function plotData(src,event)
    persistent tempData;
    global data 
    if(isempty(tempData))
         tempData = [];
     end
     plot(event.TimeStamps, event.Data)
     tempData = [tempData;event.Data];
     data = tempData;
end

2) Use NotifyWhenDataAvailableExceeds property (This decides when 'DataAvailable' is called. So if you don't want a live plot then this is suitable. Just set this to s.Rate * s.DurationInSeconds.

and have a callback for DataAvailable as:

function collectData(src,event)
     time = event.TimeStamps;
     data = event.Data;
     plot(time,data)
     save log.mat data time
     disp(‘Background Acquisition complete’);
end

This should save the data to a matfile.

3) Write Data to a file:

function acquireData
s = daq.createSession('ni');
s.addAnalogInputChannel('cDAQ1Mod1',0,'voltage')
s.Rate = 2000
s.DurationInSeconds = 5
fid = fopen('log.csv','w');
lh = s.addlistener('DataAvailable',@(src,event)saveData(fid,event));
s.startBackground();
while(~s.IsDone)
end

function saveData(fid,event)
     time = event.TimeStamps;
     data = event.Data;
     plot(time,data)
     fprintf(fid,'%f,%f\n',time,data) 
end

[avinash pabbireddy]

can u help me with the real time data plat s = daq.createSession('ni'); s.addAnalogInputChannel('cDAQ2Mod1', 0, 'Voltage'); s.addAnalogInputChannel('cDAQ2Mod1', 1, 'Voltage'); s.Rate = 2000 s.DurationInSeconds = 20; s [data,time] = s.startForeground; plot(time,data); xlabel('Time (secs)'); ylabel('Voltage') h = s.addlistener('DataAvailable', @plotData); function plotData(src,event) plot(event.TimeStamps, event.Data) end

[mado]

can i use the first method with usb6008 to aquire data and save file ?

[OJ27]

Hi,

I have been able to capture data in the background from a sensor while rotating it with a servo. However, I would like to apply an average filter for the collected points data. Could it be done in the function that is created for the listener? For example, I would like to average 10 samples before the rotating the servo to the next position.

[Tim Helps]

Hi Chriag,

Thanks for these solutions!

However, when I used them I noticed one problem with your tempData variable - since it's persistent, the data will be there still after the acquireData function is completed. If the acquireData function is run again, the previous data will still be there and tempData (and thus data) will continue to grow.

I've fixed this in my code by making it a global rather than persistent variable, and using: clearvars -global at the start of the acquireData function.

If you have a better solution please let me know!

Many thanks, Tim

[Alexandre Piccini]

Hey,

I come from the future just to thank you for this. Just what I was looking for :)

Greetings

Answer 2

[Nuno Martins]

Thank you very much Chirag Gupta, it worked like a charm. You saved me a lot of time.

[avinash pabbireddy]

function nidaq9234

global data
s = daq.createSession('ni');
s.addAnalogInputChannel('cDAQ2Mod1',0,'voltage')
s.addAnalogInputChannel('cDAQ2Mod1', 1, 'Voltage');
s.Rate = 2000
s.DurationInSeconds = 20
lh = s.addlistener('DataAvailable',@plotData);
s.startBackground();
% Do something
while(~s.IsDone)
end
close(gcf);
plot(data); %  plot global data
function plotData(src,event)
    persistent tempData;
    global data 
    if(isempty(tempData))
         tempData = [];
     end
     plot(event.TimeStamps, event.Data)
     tempData = [tempData;event.Data];
     data = tempData;
end

i'm getting error while running the code

Error: File: nidaq9234.m Line: 26 Column: 1
The function "plotData" was closed
 with an 'end', but at least one other function definition was not.
 To avoid confusion when using nested functions,
 it is illegal to use both conventions in the same file.

[Walter Roberson]

You need to add one more 'end' to this, either right after the plot(data) or at the very end. For your code structure, right after the plot(data) would make the most sense.

Answer 3

[jenni]

Is it possible to add a timer function to this code? I want a function to be executed once in every 2 sec?

Answer 4

[Csaba]

Hi Chirag Gupta!

Do you know how to get the same result with a NI DAQ-6052E PCI acquisition card? I tried your code, but since I could not get any CompactDAQ device detected:

>> d=daq.getDevices

d = 

No data acquisition devices available.
Click here for a list of known vendors.
Click here for troubleshooting tips.

??? Error: File: F20110718_AIAO_test_v15.m Line: 7 Column: 1
Function definitions are not permitted in this context.

the following line did not worked:

s.addAnalogInputChannel('cDAQ1Mod1',0,'voltage')

Maybe my device is not meant to work with sessions. It would be a shame, because the event detection would be very useful for me.

Indeed, my goal is to acquire 4 different signals on 4 different analog input through the NI BNC-2110 and the NI DAQ-6052E PCI card, plot them "live" as well as output "live" 3 different voltages (each would be a given function of the input voltages) on 3 different analog output.

Thank you very much! Kind regards,

Csaba

[Chirag Gupta]

As of MATLAB R2011a, only Compact DAQ devices are supported with the Session based architecture described above. You can try the R2011b prerelease (download from the MathWorks website) that supports other NI boards with the new architecture.

Otherwise, you can look at this demo:

"Continuous Acquisition Using Analog Input"

Answer 5

[Dagmar Fraser]

OOh top work - been looking for something like this for literal years!

I had to change

    % Do something
    while(~s.IsDone)
    end

to

    s.IsDone % will report 0

    s.wait() % rather than while

    s.IsDone % will report 1

[Christos]

hi! i would like to ask if it is possible to use the following code:

s.addAnalogInputChannel('Dev1','ctr0','EdgeCount'), in order to get the Edge count value from NI card usb 6221?

Thanks for your help