GSK DA98E Series, User Manual

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Chapter 1 Summary
5
Figure 1-4 Full-closed loop control
Figure 1-5 Semi-closed loop control
z PID Control: Also called PID regulation, it is the common algorithm used by the controller
for mathematical treatment of the input data (setting and feedback). “P” is the abbreviation of
“proportional” and refers to the linear proportional relationship between the input and output of a
controller. The bigger a proportional control factor is, the more sensitively the system will respond and
the smaller (cannot be completely eliminated) the steady state error will become. Excessive
proportional control factor leads to the disturbance and instability of the system. “I” stands for
“integral” and means the influence of controller input time integral upon output (input gradually affects
output). The bigger an integral time constant is, the more smoothly the system runs without steady
state error and the slower the system responds. “D” is the initial of “Differential”, indicating the
influence of input differential (the slope of input change). Differential control can forecast, produces
advanced correction, reduces following error and improves dynamic performance. Excessive
differential coefficient may cause system disturbance and instability. Proportional, integral and
differential controls influence each other. In a specific control system it is required achieve the
balance of the response speed, control accuracy and stability by adjusting the PID control parameters.
As differential control tends to produce impact and unsteadiness, the servo system described herein
employs PI control, i.e. only proportional and integral control.