ChE 433 D( V )PCL Highlights What I want you to take away on a 3 x 5 card
Define the control problem … - Macro vs. Micro - Deterministic vs. Heuristic - Self-regulating and non self-regulating - Dead time, how much compared to lags - Linearity, is the process linear with load?
Accuracy vs. Repeatable
Errors accumulate √ 2
Hysteresis and Dead band – Did your valve move, how much?
Filters, only when necessary! - Do not use digital filter for electrical noise! - 3 second filter time constant for hydraulic noise - Filters add control lag
Make that signal linear!
Linear signals allow the same controller settings for all loads! Determine L, compensating equation is 1/L
Controller modes, tuning … - Why not use proportional only? - PI will work most of the time - Consider Lambda, reset setting cancels the combined process lag - Ultimate period method more accurate than graphical method
Tuning … - Bode plot shows minimum gain at critical frequency
The operator might not like your idea of good control!
Lambda Tuning Set the reset value to cancel the total process time constant.
Lambda Tuning; The Reset cancels the total process time constant
Feedfoward … If you can measure the disturbance, consider using the measurement as a “feed forward” signal to anticipate the disturbance
Flow Control … Low gain, due to noise, fast reset, no rate Equal percentage valve trim
Level Control … Will proportional only do? Regulating or non-self regulating?
Pressure Control … Regulating or non-self regulating? Gas or liquid? That is compressible? Liquid pressure can be tuned like flow loops
Temperature Control … Heat transfer depends on velocity Set point profiles for batch
Temperature Control … Sensor placement
Temperature Control … For steam service, condensate removal
Multivariable Control … Can Tuning remove the interaction?
Multivariable Control … Relative Gain Array shows interaction Model control