Sample rate in Analog Input/Output blocks in Simulink

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Anna
Anna 2025-2-12
回答： Avni Agrawal 2025-3-20
I am preparing a class assignment with NI myDAQ where the sample rate should be a variable to be defined by the students.
Sample rate should be a variable in the workspace so students can change it according to results from previous computations on the system itself.
If I try to insert a variable, defined in the workspace as a positive number, I get error. Is there a workarounf for it?
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Anna
Anna 2025-2-12
If I try to enter N as Sample rate in the block parameters (N exists in the workspace and N=50) I get the message that: "Sample rate must be specified as a positive real number".

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回答（1 个）

Avni Agrawal
Avni Agrawal 2025-3-20
Hi Anne,
I understand that you are trying to use NI myDAQ with Simulink, setting the sample rate as a variable from the MATLAB workspace can sometimes cause issues. Here's how you can work around this:
1. Define the Variable Before running your model, ensure the variable is defined in the workspace. For example:
N = 50; % Sample rate, can be changed by students
2. Use a Constant Block: Instead of directly entering the variable into block parameters, use a Constant block:
  • Drag a Constant block into your model.
  • Set its value to `N`.
  • Connect it to the block where the sample rate is needed.
3. MATLAB Function Block: If you need more flexibility, use a MATLAB Function block:
  • Add a MATLAB Function block to your model.
  • Inside the function, use `N` to set the sample rate.
function y = setSampleRate(N)
y = N; % Use N as the sample rate
end
4. Parameterize the Model: Ensure your model is set up to use workspace variables:
  • Go to `Simulation` > `Model Configuration Parameters`.
  • Check the `Data Import/Export` settings to allow workspace variables.
By following these steps, you can successfully use a workspace variable as the sample rate in your Simulink model with NI myDAQ.
I hope this helps!

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