order of transfer functions

[etruyen]

This problem puzzles me...

I have a physical system which I try to model by describing every component by its tranfer function.

However, I noticed that the order in which I place these components plays a role in the output that is generated by the vi.

From a theoretical point of view, the blocks in serie might be replaced by an equivalent transfer function, i.e. their product.

But I noticed that a different sequence of the blocks, (but the same glabal transfer function) gives different results.

To keep the link with the physical system I would like to keep working with the seperate components.

I included a file to illustrate the problem: Three times the same open loop transfer function, but two different results...

Are there recommendations on the order I should put them in? And what is the cause of this?

Thanx,

Elie

[James.M]

Floating point arithmetic itself has rounding issues that are very well known and are an accepted issue. Here is a resource for more info.

That might be the source of your discrepancy. Essentially the operations could each have their own different rounding errors, which would result in a different output when stacked up in different orders.