大 Well Known issue: Sensor HIghly nonlinear 2)Maintenance (Titration Curve) If not carefully maintained the sensor gain and time H constant can vary significantly causing severe control problems 00.20.40.60.81.01.21.41.61.82.0 Ratio of reagent to influent Flow ★ G C. Goodwin-Bode Lecture 1999
G.C. Goodwin - Bode Lecture 1999 Well Known Issue: Sensor Ratio of Reagent to Influent Flow 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 1) Highly Nonlinear (Titration Curve) 2) Maintenance If not carefully maintained the sensor gain and time constant can vary significantly - causing severe control problems. pH
The above issue is important (especially from a Bode/Fundamental Limitations perspective) but there are other issues arising from the actuator Reagent Control value Non-ideal ! ★ G C. Goodwin-Bode Lecture 1999
G.C. Goodwin - Bode Lecture 1999 The above issue is important (especially from a Bode/Fundamental Limitations perspective) but there are other issues arising from the actuator Reagent Control Value ( Non-ideal !)
大 Problem(Actuator Ranging) Control valve large enough to go from pH 11>7 104 change in ion concentration %o error in valve= 102 change in ion concentration Final ph error7±2! ★ G C. Goodwin-Bode Lecture 1999
G.C. Goodwin - Bode Lecture 1999 Problem (Actuator Ranging) Control valve large enough to go from pH 11 7 104 change in ion concentration 1% error in valve 10 2 change in ion concentration Final pH error 7 2 !
大 Control System Design (Issues Multiple valves are needed to achieve desired accuracy Assume valves 5% accuracy 10 1→)9.6 7 8.6 9.6→8.3 stages 7.3 ★ 8.3→7 6.7 G C. Goodwin-Bode Lecture 1999
G.C. Goodwin - Bode Lecture 1999 Control System Design (Issues:) Multiple valves are needed to achieve desired accuracy. Assume valves 5% accuracy 11 9.6 10 7 9.6 8.3 8.6 7 8.3 7 7.3 6.7 3 stages
大 Recall Smoothing of the effect of input disturbances is provided by mixing in tanks of different sizes Tank 3 Tank 2 Tank I Large) (Medium) (Small) Spectral density 400 20 x Similar to Sub-Band coding in communications ★ G C. Goodwin-Bode Lecture 1999
G.C. Goodwin - Bode Lecture 1999 Similar to Sub-Band Coding in Communications Recall Smoothing of the effect of input disturbances is provided by mixing in tanks of different sizes. max 400 20 1 1 Spectral Density Input Tank 1 (Small) Tank 2 (Medium) Tank 3 (Large)