[airbreather]

ratio controller example is like pump at 100% when tank at 90%, 0% when 70% and interpolated inbetween

pump % = (level% - 70) * 5

limited between 0 and 100

so fuller the tank, harder the pump works, in steady state an equilibrium point will be reached somewhere in the range relative to inflow vs outflow rates.

It gives less surging downstream, at the cost of a known setpoint, just has a working range.

It might have marginally have less capacity compared ti PID, as the pump wont jump up to 100% immediately a surge comes thru at all levels, but that also depends on PID loop tuning.