Problem in Control and Simulation

[Waqar123]

I was working in control and simulation module of NI Labview 2013 and created a VI as shown in the attached file but i do'nt understand the output of the VI.

I applied a unit step input to Transfer function = 1/(s+1), and the desired output (exp(-t)) is shown in green colour (Drawn by me in MSPaint) but it displays the output as the one shown in red colour.

As the inverse Laplace of 1/(s+1) = exp(-t), the graph should be having a value of 0.3678 at t = 1 and 0 value at t --> infinity but the output (red) is exactly opposite.

Some one can please explain the output that why is it like this??

Regards

[Poolean · Accepted solution]

When applying a step response, you have to multiply your transfer function by 1/s to account for the step input before performing the Laplace Transform to obtain the correct result. In your case, the transform yields: (1 - e^(-t))

There are lots of explanations of step responses online, but here's one.