TABLE OF CONTENTS This exercise will give some practical experience in the closed loop tuning method. Figure Ex. 8.1 shows the diagram of a typical control loop. The steps for tuning are explained in the Chapter 5 tuning of closed loop control systems .
Call up the training application General single loop with interactive PID (real form).
Then, call up the detail display F3 and change MODE to MANUAL. Set the OP to 50% and wait for the process to settle down. Make a good judgment about noise observed on PV and set the digital noise filter (TD) accordingly. A good value of TD will result in a still noticeable but very small magnitude of noise in the PV term. The noise filter has to be set up before tuning in order to have it included in the results of the tuning exercise. Practically, the noise filter becomes part of the process as far as loop tuning is concerned.
For the closed loop tuning method, we have to change the tuning constants in such a way as to obtain P-control only. Change T INT to 999, T DER to 0 and K to a relatively low value of 0.5. Then, change MODE back to AUTO and make a small change of SPE in order to find out how sensitive the process is in responding. We have to find a value for K so that the closed loop will oscillate with...
