[Linear System] What is the order of the system?

[EdajMay]

Hi,

I plotted two Bode plots on MATLAB, and I'm wondering what's the system's order, because the magnitude plot looks like a first order (-20 dB/ dec) whether the phase plot looks like a second order (-180 degrees).

I'm leaning towards a first-order system since the magnitude is more precise.

However, what could explain the difference between the two plots? Is it possible to obtain those plots?

Thank you

 

[NascentOxygen]

If the phase can approach -180° then it's not well approximated as a first-order response. You are trying to fit your points around a curve with a single break point, but could you do better with two break points—a second-order response but where the poles do not co-incide?

 

[LvW]

The phase plot looks rather strange because - for a second-order system - the phase must APPROACH the 180 deg line for infinite frequencies.
Most probably, a measurement error.

 

[berkeman]

Hi,

I plotted two Bode plots on MATLAB, and I'm wondering what's the system's order, because the magnitude plot looks like a first order (-20 dB/ dec) whether the phase plot looks like a second order (-180 degrees).

I'm leaning towards a first-order system since the magnitude is more precise.

However, what could explain the difference between the two plots? Is it possible to obtain those plots?

Thank you

How did you obtain this data to plot? I agree with the others that it looks like there are errors in your data. The attenuation looks to be -25 or -30dB/decade, but without another decade higher plotted, it's hard to tell. And the phase plot looks all wrong for either a 1st or 2nd order system.

Can you show the schematic of the circuit you measured, and show the equipment used to make the measurements? Can you share the raw data?