Units for Time in Simulink

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Walter Franklin
Walter Franklin on 3 Dec 2020
Answered: Giampiero Campa on 29 Oct 2021
For a continuous model what sets the time(scale?) in a simulink model?
As an example for openExample('simulink_general/sldemo_househeatExample') the scope x axis units are in hours. What sets that?
I know this is likely a trivial question, but my real aplication is to model transients in a physical thermal system without simscape. So far, the only way I have been able to match my hand calculated estimates using (with Q being the energy input each second) has been to use a descrete solver with a timestep of 1s but I know that I am going about things the wrong way.
Thank you for any guidence you can provide!

Accepted Answer

Jonas
Jonas on 3 Dec 2020
Edited: Jonas on 3 Dec 2020
Simulation time is always seconds.
In this particular model, they just adjusted the parameters (like heat power) such that 1 second corresponds with 1 hour. For the Heater, I see they multiply the parameter c with 3600. Also, they multiply the heat losses through the windows of the house with 3600. This way, every second the heat corresponding with one hour is generated. The x-axis can then be regarded as being in hours.
Otherwise the simulation would take way too long and would need to run 24*60*60 = 86400 seconds for it to finish just 24 hours. Now it finishes in just 24 seconds.

More Answers (1)

Giampiero Campa
Giampiero Campa on 29 Oct 2021
It is not seconds, it's an "unit of time" that you can relate to time units how you want, depending on your application. See also this: https://stackoverflow.com/questions/18650928/can-simulation-stop-time-in-simulink-be-compared-with-real-time

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