Continuous sample time is not supported by discrete derivative

Hello:

I want to know if there exist typical causes for having errors when dealing with discrete derivative block in Simulink. My error is:

"Continuous sample time is not supported by block 'Controller)/Controller/increment/Discrete Derivative/TSamp'"

Although it is a discrete system, it says somthing like a continuous signal is arriving to this block and this is not supported. I have realized before that when there exist huge variations of the input signal in the first time steps, the same o similar error appears.

Thank you in advance

Answer 1

[Arnaud Miege]

Without seeing the model, it's difficult to be specific, but it sounds like you are trying feed a discrete block with a continuous signal. Insert a Rate Transition block with the appropriate sample time before the discrete block and that should fix it. You should also read the section of the documentation on Working with sample times.

HTH,

Arnaud

[Javier Guiterrez]

This rate transition block does not work. My problem comes from before in the diagram. A variable that is calculated from algebraic operations cannot be derivated either.

[Javier Guiterrez]

i do not know if it is meaningful, but the following warning also appears:

Warning: Discontinuities detected within algebraic loop(s),

may have trouble solving

Thank you

[Arnaud Miege]

Can you upload your model to a filesharing site? It's difficult to answer your question without seeing the model

[Javier Guiterrez]

I am sorry that the model is confidential. Now I am out of the office until monday. If I can I will create a similar example for you.

Thank you

[Javier Guiterrez]

Hello again:

I have made a photo to show you my problem but i cannot find how to upload. Please tell me and I will update.

Thank you

[Arnaud Miege]

There's no built-in mechanism for uploading files on MATLAB Answers. Have a look at this question for other possibilities:

http://www.mathworks.co.uk/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

[Javier Guiterrez]

Finally it is not necessary to upload the photo but thank you anyway.

The problem is solved. The sample time of the used constants was inf. After changing them to a certain value, this problem is solved.

Thank you

[Arnaud Miege]

Cool, glad it's resolved. Next time, you may want to use the sample time colours to highlight any problems:

http://www.mathworks.com/help/releases/R2011a/toolbox/simulink/ug/f4-93620.html#f4-93674

http://www.mathworks.com/help/releases/R2011a/toolbox/simulink/ug/bry66ow.html#bry66rv

[Nits]

I am having a same issue but I am feeding buffer from Dspace serial receive block. I tried putting rate transition block with default settings, still i am getting the error mentioned below:

All sample times must be discrete. No continuous or constant sample times are allowed.

Looking forward to your solution.

Thanks

[Firas]

It worked for me thanks