Centrifugal compressor anti surge

[Indy]

Hi
I posted this thread in the electrical engineering section but it may be better suited here. I’m just trying to understand why compressor Anti-Surge controllers take temperature and pressure signals from the suction side and also the discharge side along with flow to then modulate a control valve to recirculate a portion of the flow back to the suction side to prevent surge occurring.

I suppose I am asking why are the signals not just taken from the compressor discharge side ? Can’t see what I’m missing.

Thanks

 

[Indy]

Thanks again.
Still not 100%sure why the inlet P is in mBar as is the outlet F (via orifice plate) but the outlet P is in Bar?

Thanks