ABSTRACT
This chapter discusses a more detailed description of loop operation and its implicit mathematical relationships. In the feedback loop, the variable to be controlled is measured and compared with the desired value— the set point. The resonant oscillator uses a device that requires a minimum of added energy each cycle to maintain oscillation. The nonresonant oscillator is simply an amplifier with some type of phase-shifting network between output and input. Two-position control is nearly always the simplest and least expensive form of automatic control. Any of the forms discussed can be implemented with commercially available mechanical, pneumatic, or electronic instrumentation. Proportional or throttling control was developed to meet the demand for a more precise regulation of the controlled variable. Throttling control indicates any type of control system in which the final operator is purposely positioned to achieve a balance between supply to and demand from the process.
