How to determine the moment (time) at which the signal exceeded the set value in simulink?

If I have a signal defined by exponential function (for example): 2e^t. How do I determine time when the value of this function will be more then (for example) 5?

Answer 1

[Jonas]

Put an integrator block with input 1 inside an enabled subsystem. Use a relational operator to see if your exponential function value is above 5 and use it for the enable port of the enabled subsystem. The output of the integrator will give you the time.

[Marko Boskovic]

Dear Jonas,

Can you please send me an example of system you talking about?

Regards,

Marko

[Tiago Moraes]

Here an example:

[Tiago Moraes]

Explaing the example:

Inside subsystem we have an integrator. Simulation time: 12s.It's generated a pulse with period 4s and pulse width 22%. So, per clicle, the pulse is high during 0,88s. In 12s, we have 3 cycles. So, the integrator result is 2,64s (3 x 0,88s). It works!

[Jonas]

Instead of using an integrator I just used the clock directly.

Answer 2

[Fangjun Jiang]

Assume you build your model correctly, your signal varies as time goes. Compare your signal with the Constant value, its output will be a true or false signal. Use this signal to trig a tiggered subsystem, which contains a Clock block inside. Play with it and you should be able to get what you want.

[Marko Boskovic]

I can do the same with the block ''MATLAB function'', but I don't get what I want. I want to determine at what point this function exceeds a certain value, and to use that moment as the time when I will call another function (because that other function is not active until that moment). For example I have a function x^2, the function x-2 should be run at the moment when the function x^3 exceeds the value 4, so I need to have number (time when fuction is higher than certain value) on output. How do I determine that moment, can I do that using for or while loop in block ,,MATLAB function''?

[Fangjun Jiang]

I can see that it can be done using a MATLAB Function block, but no need to use FOR or WHILE loop. Keep in mind that the MATLAB Function block is executed at every simulation step.

Did you try the method I suggested? That is a more straightforward method.