2nd, or 4th order filter

[MillionHorns]

Hello!

I am attempting to low-pass filter some force data. I have set up what I believe to be 4th order, zero phase shift filter (via a 2nd order recursive filter). However, there seems to be much debate on the accuracy of my code. Some people seemingly believe that my code equates to a 2nd order filter. They believe that within the butterworth code in LabVIEW, it "controls" this somehow. 

Thoughts on my code and whether it is or is not a 4th order zero phase shift? Do you have sources for your thoughts? Trying to get this right, but I need sources to convince my boss (my PhD adviser). 

Thanks! 

ps  - my first post!!!  

[Titen]

Hi MillionHorns,

While I can't comment much on your filtering setup, the Butterworth Filter in LabVIEW does indeed control IIR 4th Order vs IIR 2nd Order within the filter structure options. Does exploring the contents of the Butterworth Filter vi help clear up any of the functionality?