Controller, with complementary feedback

The regulation of ribonucleotide reductase is complex, with many feedback reactions used to keep the supplies of deoxynu-cleotides in balance. For example, dGTP and dTTP are feedback inhibitors of their own formation. Each is also an activator of the synthesis of the complementary nucleotide (dCDP or dADP), while dATP is an inhibitor of the reductions to make dADP, dCDP, dGDP, and dUDP. These control functions keep the supply of deoxynu-cleotides in balance, so that a roughly equivalent amount of each remains available for DNA synthesis. 

A proportional-plus-reset controller applied to the same process, and adjusted to produce 22.5 phase lag, can serve as a reference for compaii son. The values of reset time and proportional band required for )- 4-ainplitude damping were calculated for selected ratios of trated error per unit load chan was then found as the PR product, to compare with that obtainable through complementary feedback. This information is plotted in Fig. 4.16, with coordinates... 

The foregoing discussion on complementary feedback was based primarily on critically damped response. With a pure dead-time process, this was the best obtainable. But with less difficult processes, lower damping will enhance recovery from load disturbances due to greater controller gain. 

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