problem with sine-wave and scope component in simulink

i'm a begginer and trying to learn simulink. following a sample on mathworks site i put a sine-wave and a scope in a simple model. the problem is the shape of sine-wave if remain the frequency at 1 the sine-wave shape is correct but if change the frequency it'll not become like a sine-wave more like a distortion or ramp. i don't know what is the problem.

[Leopoldo Pavesi]

I had the same problem. I regularly use without any problems matlab and simulink for my automatic control lectures, but i needed to generate a sine wave and was frustrated. I believe Kaustubha has given way tp overcome this situation. Many thanks to her

Answer 1

[Kaustubha Govind]

I think the issue is that Simulink is not using a small enough time-step so that the signal is completely rendered on the scope (think of it like an aliasing effect). See Choosing a Solver for more information on you should configure the solver used for your model (which is what determines what time-step Simulink uses). Since you are a beginner, I'm assuming that you are using the default solver, which is a variable-step ode45 solver (from the model menu, Simulation->Configuration Parameters...>Solver). As you can seen, the "Max step size" parameter is set to "auto" by default, which means Simulink automatically tries to determine how large a step it can take so as to preserve your signal's shape - which is why, you probably see that the general shape of the signal is preserved, but details are lost. You can restrict this to a small value (say 0.01), save the new settings and try simulating again. If you still some distortion, lower the value further - at some point it should give you the signal shape you expect.

[shmd]

thank you that was the exactly problem

[Rishiraj Sarker]

Very helpful reply :)

[pranab nath]

great..tnx

[Govinda Nahak]

thank you..

[Lohith Venugopal]

Thank You....

[E S]

I was in a hurry and it helped me a lot! Thank you!

[brn ny]

yes it worked..thanks Kaustubha. reduce the max step size .if it doesn't work...keep decreasing (even up to 0.00001)

[Wail Saleh]

Thank you very much for the question and for the answer from Kaustubha. I suffered from the same problem for a long period. Now, it is resolved. Thanks again.

[SATYANARAYANA CHANDAKA]

Thank you very much

[SANDEEP PV]

Thank you very much Kaustubha.

[Juliette Bowman]

Amazing, worked a treat. Thank you so much!

[piyush kumar]

yes it really helped, thanks. We need more people like you to help MATLAB community

[Bhamini Sreekeessoon]

Thank you. It works.

[AMINE]

I express my heartfelt gratitude.

[Nam Hoang]

You are a god send. Thank you so muchhhhhhhh

Answer 2

[Guy Rouleau]

You might be interested by that:

http://blogs.mathworks.com/seth/2009/07/14/refining-the-output-of-a-simulation/

[shmd]

thank you Guy

Answer 3

[Salman]

Choosing Maximum Step Size in a Simulink Solver

Example model: Sine Wave Block → Scope Block

When using a sine wave block with frequency 10 rad/sec, the signal often looks not smooth in the Scope.

This happens because Simulink automatically chooses a maximum step size = 0.2, based on three built-in MATLAB rules:

1. Step size < Period ÷ 3

- Frequency = 10 rad/sec → Period = 1/f = 0.6 sec

- Period ÷ 3 = 0.2 sec

2. Step size < (Stop Time – Start Time) ÷ 50

- (10 – 0) ÷ 50 = 0.2 sec

3. Step size must be a fraction of (Stop Time – Start Time)

- Examples: 0.1, 0.2, 0.05, etc.

So with step size = 0.2 sec:

Points per sine cycle = Period ÷ Step size = 0.6 ÷ 0.2 = 3 points per cycle

But 3 points per cycle are not enough for a smooth sine wave.

For smooth display: use 50–100 points per cycle

Better step size choices:

0.6 ÷ 50 = 0.01 sec → smoother wave

0.6 ÷ 100 = 0.006 sec → even smoother wave