Do I need to arm a counter attached to NI DAQ USB 6341 to begin data acquisition?

I have a USB 6341 NI DAQ that is connected to a photon counter configured to count edge counts. I am trying to trigger the counter's data acquisition using an external start-trigger (PFI line connected to a delay stage). It seems that edge counts require pause-triggers rather than start-triggers (a pause-trigger is not allowed in Matlab). I am getting the error "USB 6341 (BNC) does not support external triggers for the CounterInput subsystem)."

Is it possible to acquire data without using a trigger or does the counter need to be armed to begin data acquisition? Alternatively, is it possible to configure a pause-trigger in Matlab? Any help would be appreciated. The code to intialize the counter is below.

det = daq('ni'); %initialize USB 6341 Daq

ch = addinput(det,"Dev1", "ctr1", "EdgeCount"); %Initialize counter for edge counts

addinput(det,"Dev1","ai0","Voltage"); %Add dummy analog channel to clock counter input

ch.ActiveEdge = 'Falling'; %Count on Falling edge of edge counts

get(ch) % get information on counter channel

addtrigger(det,"Digital","StartTrigger","External","Dev1/PFI9") %Initialize trigger

det.Rate = samplerate*samplepoint; %data collection rate

Answer 1

[Aravind]

Hi @Sanjna,

You do not need to "arm" the counter before starting the counting process. On the NI USB-6431, the counter input channels begin counting as soon as the session is started in MATLAB by calling start(det). There is no separate "arming" step required for the counters.

As of MATLAB R2024b, according to the documentation found here: https://www.mathworks.com/help/daq/daq.interfaces.dataacquisition.addtrigger.html, the Data Acquisition Toolbox supports only a start trigger. The NI USB-6341 does not support start triggers for the Counter Input subsystem, which is a hardware limitation for this device in combination with MATLAB/Data Acquisition Toolbox. The error message "USB 6341 (BNC) does not support external triggers for the CounterInput subsystem" arises due to this reason. Unfortunately, there is no workaround for this, and implementing pause triggers in MATLAB is not possible.

If your goal is simply to acquire data, you can proceed without any triggers. By calling start(det), you initiate the session, and both the analog input and counter input will begin reading together, with the counter starting couting immediately.

Alternatively, if you need a "trigger" condition to start reading, consider implementing a software-based trigger. This involves using a software loop to monitor a digital or analog channel for specific events, which can act as your "trigger". Once the event is detected, you can call start(det) to begin the session.

I hope this answers your question. If you provide more specific details about your use case, I can offer more targeted advice.

[Sanjna]

Hi Aravind,

Thank you for your response. I do need a "trigger" condition. How would I implement a software-based trigger? How do I set up a digital or analog channel that can monitor specific events that act as my trigger? Can I configure these to my external trigger (a delay stage that should send a trigger when it starts moving and stops moving) such that the counter starts taking data when triggered (stage starts moving) and stops taking data when triggered (stage stops moving)?