Matlab function: c2d => what does sample time

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Alex 2011-8-15

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Hi all.

I'm trying to convert a continues transfer function into a discrete. I know that the matlab function c2d can be used to this purpose. But what does the sample time? I mean, if I late choose to work with a signal with a different sample frequency, would I then need to convert the filter again, and why?

[sysd,G] = c2d(sys,Ts,method)

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Answer 1

Paulo Silva 2011-8-15

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That's just the sampling time of the conversion of your transfer function from continuous to discrete (each method has it's own formula and the Ts is part of it, see the methods and formulas in books like Digital Control of Dynamic Systems), you can change the sampling time of the input signal without convert again but you must be careful with the sampling times, plot the continuous and discrete response to your input on the same axes and see if they are similar, low Ts values require more processing power but result in better responses, high Ts values require less processing power but don't give good results, you must make a compromise and choose the Ts that satisfy your project requirements.