TABLE OF CONTENTS This exercise will introduce a combined proportional and integral control action of controllers. Special emphasis is given to the elimination of the remaining offset of proportional control without loss of control speed. It will be shown that the combination of proportional and integral control maintains the speed of control as it exists with proportional control only, but without the disadvantage of an OFFSET term. Figure Ex. 2.1 shows an example for closed loop control.
Call up the training application single flow loop. After this exercise has been called up, press F3 to get the detail display of the flow controller (Figure Ex. 4.1).
To prepare the controller for PI-control, change K (gain), T INT (integral time constant) and T DER (derivative time constant). Set K to 0.8, T INT to 1 and T DER to 0.
To study PI-control, change SPE from approximately 300 (60% of range) to approximately 125 (25% of range) as shown in Figure Ex. 4.2.
It can be seen, that combined proportional and integral control moves the PVE value closely towards the value of SPE. No offset is left, as would have been with proportional control only. There has also been no noticeable loss of speed of control. Close observation of the trend display (see Figure Ex. 4.2) first reveals a fast change of PVE, followed by...
