Brooks 5866, Инструкция по установке и эксплуатации, Страница: 19 / 66

Brooks Instrument Model 5866 Pressure Controller
3-2
Proportional Control
Proportional control is a basic continuous control mode in which the
controller output is proportional to the error input signal to the controller.
Refer to Figure 3-2. It provides very rapid response and is relatively stable.
Used alone, proportional control has one major disadvantage: at steady
state it exhibits an offset. That is there is a difference between the desired
value, or setpoint and the actual value of the controlled variable. An
integral action added to the proportional mode eliminates offset.
Integral Control
Integral or reset action is an integration of the input error signal over time.
Refer to Figure 3-3. This means that with integral action the value of the
manipulated variable changes at a rate proportional to the error. With
integral action present there can be no offset at steady state since the
manipulated variable will continue to change as long as an error is present.
Characteristics of P.I. Control
By using both proportional and integral control actions, rapid control can
be achieved with out a steady state offset. Refer to Figure 3-4. Typically
there is a slight decrease in system stability due to the presence of the
integral mode. The dynamic response of the system is better than the
response would be with integral alone. Because the two controller modes
are interactive the P.I. controller is somewhat more difficult to tune.
Tuning the P.I. control
Turning the P potentiometer clockwise (c.w.) will increase the proportional
band thus increasing the offset and system response time. If the
proportional band is too low, the system may overshoot the command, or
oscillate. Turning the I potentiometer counterclockwise (c.c.w.) will increase
the integration time, making the system respond slower, but more stable.
Adjust the P and I potentiometers until the optimum response is achieved.
Check the adjustment in the system over the expected range of pressures
and flows.
Fastest controller response to set point changes are obtained with the P
potentiometer fully counterclockwise and the I potentiometer fully
clockwise.