Units for Time in Simulink

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!

Answer 1

[Jonas]

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.

[Walter Franklin]

Thank you!

[Steven Lord]

So "by the book" seconds could seem like hours. Regulation 46A.

Answer 2

[Giampiero Campa]

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