英语翻译Reading Material Tuning of the PID Controller The PID al

英语翻译
Reading Material Tuning of the PID Controller The PID algorithm is the most popular feedback controller used within the process industries.It has been successfully used for over 50 years.It is a robust easily understood algorithm that can provide excellent control performance despite the varied dynamic characteristics of process plant.Controller tuning involves the selection of the best values of Kc,Ti and TD (if a PID algorithm is being used).This is often a subjective procedure and is certainly process dependent.A number of methods have been proposed in the literature over the last 50 years.However,recent surveys indicate:(1) 30 % of installed controllers operate in manual.(2) 30 % of loops increase variability.(3) 25 % of loops use default settings.(4) 30 % of loops have equipment problems.A possible explanation for this is lack of understanding of process dynamics,lack of understanding of the PID algorithm or lack of knowledge regarding effective tuning procedures.This section of the notes concentrates on PID tuning procedures.The suggestion being that if a PID can be properly tuned there is much scope to improve the operational performance of chemical process plant.When tuning a PID algorithm,generally the aim is to match some preconceived “ideal” response profile for the closed loop system.The following response profiles are typical.
Often,with level systems exact setpoint following is not essential,hence proportional control is often used.Temperature loop dynamics can be slow because of process heat transfer lags.Dead-time is possible,especially in heat exchangers and temperature is not normally noisy.Consequently PID control is normally preferred.Flow loop dynamics are generally fast (of the order of seconds) .Control valve dynamics are normally the slowest in the loop.Flow systems are noisy.However,noise can often be dealt with simply by reducing the gain.