Quarter-amplitude damping

To summarize, a dead time of 1 min would cycle with a period of 4 min, sustained by a reset time of 2/-ir, or about 0.65 min. Quarter-amplitude damping can be achieved by halving the gain, which means doubling the reset time. Figure 1.9 shows the entire situation. 

Quarter-amplitude damping requires loop gain to be 0.5. lOO C. 

Notice that c exhibits a damped oscillation whose period is two calcula tions (two dead times). Notice also that the amplitude of successive crests is diminished by one-quarter. Finally, there is an offset. The controller output comes to rest at 16.667 percent above the bias. The offset is... 

The decay ratio is the ratio of the amplitude of an oscillation to the amplitude of the proceeding oscillation, C/B in Figure 5.2. More specifically, we can define the quarter decay ratio (QDR), which lies between critical damping and underdamping ... 

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