Simulink Integrator

Looking to go back to complete basics on how some aspects of Simulink work and am running into something mathematically that seems off. I've made a simple program with blocks (sine wave)->(1/s)->(Scope) with an additional scope set up to view the initial sine wave. I've set the amplitude of the sin wave to 1 and run the program. The sine wave plot looks correct, ±1 amplitude and the wave starts at (0,0), like a normal sine wave. The integral of a sine wave is -cos, so I expect to see a wave that runs ±1 and starts at (0,1), but what simulink outputs is a sine wave that starts at (0,0) and the amplitude runs from 0 - 2, not ±1. Am I missing something on how to set up a signal to be integrated? If I use the derivative function, I do get a cos wave. Any thoughts?

Answer 1

[Titus Edelhofer]

Hi Daniel,

you are missing the initial condition: the integration of sin is -cos(x)+X0, where X0 is at first arbitrary.

But because the integration always starts at point zero:

int_0^0 sin(x) dx  = 0

you get X0 = 1.

The curve you should see is not a sine but a -cosine shifted by one.

Titus

[Daniel W]

I see it now, makes sense. Thank you.

[Kaustubha Govind]

Daniel: Please accept Titus' answer since it has resolved your issue.