Pneumatic circuits: R, C Pressure is potential, pressure difference is voltage drop A flow restrictor is a resistance An air chamber is a capacitance DP Slope R Resistance R P+pc P+pi q C R Q pc C pi
Position to Pressure transducer/amplifiers pb Rx ps C pa Ps is pressure of supply air from wall pipe or air cylinder X is weighted differential average of input position and the pivot position X controls the pressure Pb send to the control valve
Pneumatic proportional controller Ps is const parameter Diaphragm is fast, so pc and pb are equal x is weighted diff sum of e and y Notice the direction of x and e:
Pneumatic proportional controller Since pc=pb Drawing for this part can be simplified
Proportional + derivative controller Recall: bellow pressure is related to input pressure by 1/(RCs+1) Pbellow
Proportional + Integral controller So, in closed-loop TF, replace (RCs+1) by (RCs+1)/RCs:
PID controller
Hydraulic servo system
Alternative construction
Proportional controller Same as last page Same as before
Dashpot
Proportional + Integral controller Rest as before Last page
Proportional +derivative control Spring force: k(y-z) instead of kz; new TF=1-oldTF
PID controller w Force Balance: k1z=ADP1; k2(y-w)=ADP1+ADP2
Block diagram representation
e w z
Thermal systems Conservation of heat energy: