Why is Simulink giving different output for same transfer function but with different approach?

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Aarib Irfan
Aarib Irfan on 28 Mar 2020
I have created the lower simulink model for an altitude hold autopilot system as shown in the model below. The model created at the bottom gives the correct answer. The highlighted part is used to calculate the transfer function H for height. I calculated that transfer function in matlab and then used that H function directly in the simulink. The calculated function H is correct as i have confirmed that from the book. However, i get different answer for both models. The lower model gives right answer but the upper model doesn't even come close to the correct output even though the transfer function H is correct. I can't ask my teachers because everyone is on lockdown and i really need to know what am i doing wrong. So please someone help me.
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Sulaymon Eshkabilov
Sulaymon Eshkabilov on 29 Mar 2020
It is not quite clear (1) what formulation you've entered for H function in your upper model. Moreover, it is not clear (2) what you have entered for [theeta] and [sys] in your models. Just presuming that you've done everything correctly with the [H], [theeta] and [sys], then just a guess would be gain values.

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Answers (1)

Arkadiy Turevskiy
Arkadiy Turevskiy on 7 Oct 2020
Impossible to say exactly without having access to your models. What transfer function did you calculate for H? What is the input?

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