TABLE OF CONTENTS The objective of this exercise is not to provide a guided tour through cascade control, but to introduce the student into the effects of PV tracking, initialization and Mode changes in cascade control. The other aspects of cascade control can easily be explored with the capabilities of this software package. But it is up to the student to experiment.
Call up the training application Tank level control (see Figure Ex. 11.1). At this stage no PV tracking or initialization is active. After the process has settled down, change MODE2 to MANUAL and OP2 to 30% of range. The objective is to continue cascade control when PVE1 has reached approximately a value of 70 (35% of range). As we can see in Figure Ex. 11.2 (see left side of the screen), the change of MODE2 and OP2 causes most variables within the cascade control system to drift uncontrolled (OP1, SPE1, SPE2). When PVE1 has reached approximately 70, change SPE1 to 70 and then MODE2 back to CASC.
When we change from CASC control to MANUAL (MODE2 from CASC to MANUAL) some variables are unpredictable as discussed earlier. When changing back to CASC control, these unpredictable variables cause a bump within our control system, when they have to change back to real and defined values.
Based on the observation that unpredictable values of OP1, SPE1 and SPE2 cause...
