Difference between Second order Transfer function NATIVE block vs Second order Transfer function expansion equation form

SANJEEV RACHABATHUNI

Hi

If I want to use the 2nd order Transfer Function in the Altair Embed platform, there are two ways I can take the Transfer Function Ready made block from the embed tool box or I can create a 2nd order expansion form using embed native blocks.
Functionality wise both are the same. If I give the same input to both models and it should produce the same outputs. But here I have observed there is some difference.

can you please help me to come out of this problem?

I am sharing the required diagrams, test data and Screenshots results.

 

Please check the attachment

Thank you,

Regards,

R Sanjeev

pdarnell

Hi Sanjeev,

If you drop the time step to .0001 you get much better agreement. Our transfer functions know they are linear transfer functions and take the discrete sample time into account to maintain accuracy regardless of sample time. The integrators do not, so depending on the frequency response of the transfer function you may need to shrink the time step to get good agreement.

The plot below looks at the step response region and plots the xfer block in red, and the 1/S equivalent in blue. You can see at the .0001 step size there is good agreement.