Log Analog Input Data to a File Using NI Devices

This example shows how to save data acquired in the background to a file.

Create a DataAcquisition with Analog Input Channels

Create a DataAcquisition and add two analog input channels with Voltage measurement type. For this example use a National Instruments™ X Series data acquisition device, NI PCIe-6363 card with ID Dev1.

d = daqlist("ni")

d =

  12×4 table

     DeviceID                 Description                    Model             DeviceInfo     
    ___________    __________________________________    _____________    ____________________

    "cDAQ1Mod1"    "National Instruments NI 9205"        "NI 9205"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod2"    "National Instruments NI 9263"        "NI 9263"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod3"    "National Instruments NI 9234"        "NI 9234"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod4"    "National Instruments NI 9201"        "NI 9201"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod5"    "National Instruments NI 9402"        "NI 9402"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod6"    "National Instruments NI 9213"        "NI 9213"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod7"    "National Instruments NI 9219"        "NI 9219"        [1×1 daq.DeviceInfo]
    "cDAQ1Mod8"    "National Instruments NI 9265"        "NI 9265"        [1×1 daq.DeviceInfo]
    "Dev1"         "National Instruments PCIe-6363"      "PCIe-6363"      [1×1 daq.DeviceInfo]
    "Dev2"         "National Instruments NI ELVIS II"    "NI ELVIS II"    [1×1 daq.DeviceInfo]
    "Dev3"         "National Instruments PCIe-6363"      "PCIe-6363"      [1×1 daq.DeviceInfo]
    "Dev4"         "National Instruments PCIe-6363"      "PCIe-6363"      [1×1 daq.DeviceInfo]

deviceInfo = d{9, "DeviceInfo"}

deviceInfo = 

ni: National Instruments PCIe-6363 (Device ID: 'Dev1')
   Analog input supports:
      7 ranges supported
      Rates from 0.0 to 2000000.0 scans/sec
      32 channels ('ai0' - 'ai31')
      'Voltage' measurement type
   
   Analog output supports:
      -5.0 to +5.0 Volts,-10 to +10 Volts ranges
      Rates from 0.0 to 2000000.0 scans/sec
      4 channels ('ao0','ao1','ao2','ao3')
      'Voltage' measurement type
   
   Digital IO supports:
      39 channels ('port0/line0' - 'port2/line6')
      'InputOnly','OutputOnly','Bidirectional' measurement types
   
   Counter input supports:
      Rates from 0.1 to 100000000.0 scans/sec
      4 channels ('ctr0','ctr1','ctr2','ctr3')
      'EdgeCount','PulseWidth','Frequency','Position' measurement types
   
   Counter output supports:
      Rates from 0.1 to 100000000.0 scans/sec
      4 channels ('ctr0','ctr1','ctr2','ctr3')
      'PulseGeneration' measurement type
   

dq = daq("ni");
addinput(dq, "Dev1", 0:1, "Voltage");
dq.Channels

ans = 

    Index    Type    Device    Channel    Measurement Type          Range              Name   
    _____    ____    ______    _______    ________________    __________________    __________

      1      "ai"    "Dev1"     "ai0"     "Voltage (Diff)"    "-10 to +10 Volts"    "Dev1_ai0"
      2      "ai"    "Dev1"     "ai1"     "Voltage (Diff)"    "-10 to +10 Volts"    "Dev1_ai1"

Create a Log File

Create the file log.bin and open it. The file identifier is used to write to the file.

fid1 = fopen("log.bin","w");

Set the ScansAvailableFcn

During a background acquisition, the DataAcquisition can be directed to handle acquired data in a specified way using the ScansAvailableFcn property.

dq.ScansAvailableFcn = @(src, evt) logData(src, evt, fid1);

Acquire Data in the Background

Use start to acquire data for five seconds.

start(dq, "Duration", seconds(5))

During normal operation, other MATLAB® commands can execute during this acquisition. For this example, use pause in a loop to monitor the number of scans acquired for the duration of the acquisition.

while dq.Running
    pause(0.5)
    fprintf("While loop: Scans acquired = %d\n", dq.NumScansAcquired)
end

fprintf("Acquisition has terminated with %d scans acquired\n", dq.NumScansAcquired);

Close the Log File

fclose(fid1);

Load Data from the Log File

Load file contents as a 3-column matrix into data.

fid2 = fopen('log.bin','r');
[data,count] = fread(fid2,[3,inf],'double');
fclose(fid2);

Assign and Plot the Data

t = data(1,:);
ch = data(2:3,:);
plot(t, ch);

function logData(src, ~, fid)
[data, timestamps, ~] = read(src, src.ScansAvailableFcnCount, "OutputFormat", "Matrix");

data = [timestamps, data]' ;
fwrite(fid,data,'double');
end

While loop: Scans acquired = 500
While loop: Scans acquired = 1000
While loop: Scans acquired = 1500
While loop: Scans acquired = 2000
While loop: Scans acquired = 2500
While loop: Scans acquired = 3000
While loop: Scans acquired = 3500
While loop: Scans acquired = 4000
While loop: Scans acquired = 4500
While loop: Scans acquired = 5000
Acquisition has terminated with 5000 scans acquired