How to handle multiple devices with an external trigger signal in NI-PXI platform?

I have a NI-PXI chassis(model: 1042Q) and multiple data aquisition devices(PXI-4496) for multi-channel signal acquisition and processing.

With an external digital trigger, how can I connect the trigger signal and make a matlab program. Please let me know the useful code to deal with multiple devices with an external trigger signal in a PXI chassis.

Answer 1

[R]

Hi @Hyu-Sang Kwon,

To acquire data from multiple NI PXI-4496 devices using an external digital trigger in a PXI chassis (model: 1042Q) with MATLAB, use the 'Data Acquisition Toolbox'. First, ensure the NI-DAQmx drivers and Data Acquisition Toolbox are installed. Use daqlist("ni") to identify connected devices and create a DataAcquisition object with daq("ni").

Add analog input channels from each PXI-4496 device using addinput, specifying channels (e.g., addinput(d, deviceIDs{i}, "ai0:7", "Voltage")). Configure the external digital trigger with addtrigger, setting the trigger type to "Digital", source to "StartTrigger", and condition to "RisingEdge" (e.g., addtrigger(d, "Digital", "StartTrigger", "Dev1/PFI0", "External")).

Set the sample rate and duration and start the session to begin data acquisition when the external trigger is received.

Below is a sample code you can refer:

% Ensure the Data Acquisition Toolbox is installed and NI-DAQmx drivers are available

% Step 1: List all connected DAQ devices
devices = daq.getDevices;

% Display connected devices
disp('Connected DAQ devices:');
disp(devices);

% Step 2: Create a data acquisition session
s = daq.createSession('ni');

% Step 3: Add analog input channels from each PXI-4496 device
% Replace 'Dev1', 'Dev2', etc. with the actual device IDs from the devices list

deviceIDs = {'Dev1', 'Dev2'}; % Example device IDs
numDevices = length(deviceIDs);

for i = 1:numDevices
    % Add all channels from each device
    addAnalogInputChannel(s, deviceIDs{i}, 0:7, 'Voltage'); % PXI-4496 has 8 channels (0-7)
end

% Step 4: Configure the external digital trigger
% Replace 'PFI0' with the actual PFI line used for the external trigger
s.addTriggerConnection('External', 'Dev1/PFI0', 'StartTrigger');

% Step 5: Set the rate and duration of the acquisition
s.Rate = 50000; % Sample rate in Hz (50 kHz)
s.DurationInSeconds = 10; % Duration of the acquisition in seconds

% Step 6: Start the session and acquire data
disp('Waiting for external trigger...');
[data, time] = s.startForeground;

% Step 7: Process the acquired data
disp('Data acquisition complete.');
plot(time, data);
xlabel('Time (s)');
ylabel('Voltage (V)');
title('Acquired Data from Multiple PXI-4496 Devices');
legend(arrayfun(@(x) sprintf('Channel %d', x), 1:size(data, 2), 'UniformOutput', false));

% Save the data to a file if needed
save('acquired_data.mat', 'data', 'time');

Refer to the documentation link and examples to know more:

https://www.mathworks.com/help/daq/hardware-discovery-and-setup.html?s_tid=CRUX_lftnav

Answer 2

[Hyu-Sang Kwon]

Thanks very much for your immediate reply.

I tried your code, but I got the following error message.

Because I use the Matlab 2018b version, these commands such as "daqlist" and "daq" may cause an error.

Would you modify this code for Matlab 2018b?

Thanks in advance.

-------------------------------------------------------------------------

'daqlist'은(는) 정의되지 않은 함수 또는 변수입니다.

오류 발생: Mat_answer_01 (line 4)

devices = daqlist("ni");

[R]

Hi @Hyu-Sang Kwon, I have modified the code for R2018b usage. Post R2020b release, workflow have changed from sessions based to DataAcquisition interface based workflow.

[Hyu-Sang Kwon]

Thanks again, but your code causes the following errors, unfortunately.

Please, would you solve the problem?

-------------------------------------------------------------------

>> Mat_answer_02

Connected DAQ devices:

Data acquisition devices:

index Vendor Device ID Description

----- ------ --------- -----------------------------

1 ni Dev1 National Instruments PXI-4496

2 ni Dev2 National Instruments PXI-4496

경고: A channel that does not support on-demand operations was added to the session. On-demand operations using inputSingleScan and

outputSingleScan will be disabled. Only clocked operations using startForeground and startBackground can be done.

경고: A channel that does not support on-demand operations was added to the session. On-demand operations using inputSingleScan and

outputSingleScan will be disabled. Only clocked operations using startForeground and startBackground can be done.

Waiting for external trigger...

다음 사용 중 오류가 발생함: Mat_answer_02 (line 34)

Specify StartTrigger connection for device 'Dev2'. All devices in a session should start together and use the same scan clock.

>>

[R]

@Hyu-Sang Kwon, it seems that you need to ensure all devices in a session start together and use the same scan clock. You can add this configuration before Step 5, i.e., setting the rate and duration of the acquisition:

% Ensure that all devices use the same clock
for i = 2:numDevices
    s.addClockConnection('Dev1/PFI0', deviceIDs{i}, 'ScanClock');
end

[Hyu-Sang Kwon]

I added the configuration commands and ran the program, but unfortunately, it dosen't still work.

The error message is as follows, and the command line 30 is

s.addClockConnection('Dev1/PFI0', deviceIDs{i}, 'ScanClock');

-------------------------------------------------------------------------------------------------------------------

>> Mat_answer_03

Connected DAQ devices:

Data acquisition devices:

index Vendor Device ID Description

----- ------ --------- -----------------------------

1 ni Dev1 National Instruments PXI-4496

2 ni Dev2 National Instruments PXI-4496

경고: A channel that does not support on-demand operations was added to the session. On-demand operations using inputSingleScan and

outputSingleScan will be disabled. Only clocked operations using startForeground and startBackground can be done.

경고: A channel that does not support on-demand operations was added to the session. On-demand operations using inputSingleScan and

outputSingleScan will be disabled. Only clocked operations using startForeground and startBackground can be done.

다음 사용 중 오류가 발생함: Mat_answer_03 (line 30)

Can not determine destination device and terminal name from input argument 'Dev2'. Use 'DeviceName/TerminalName' format or 'External'.

>>