04-01-2013, 10:37 AM
Controller
Controller.ppt (Size: 1.42 MB / Downloads: 59)
Controller Principles
The controller takes input, solve certain equations to calculate the proper output
The equations describe the mode or action of the controller
Process Characteristics
To select which mode of operation to used depends on the characteristics of the process
Process equation
Dynamic behavior of the process
Process Load
Set of parameters in the process that results in controlled variable equal to setpoint value, excluding controlled variable
When the load changes, the controlling variable is adjusted to compensate for this change to bring back to the setpoint
Process Lag
The time delay that process responds to the load change
Example,
An inlet flow is suddenly double. The process gradually change the liquid temperature.
Control System Parameters
Error
Variable Range
Control Parameter Range
Control Lag
Dead Time
Cycling
Controller Modes
Dead Time
Dead time is the delay from when a controller output signal is issued until when the measured process variable (PV) first begins to respond.
The presence of dead time is never a good thing in a control loop.
Reverse Action
When an increase in controlled variable cause a decrease in controller output
Temperature control
If temperature increase, the drive to the heater should be decrease
Integral Control Mode
Integral mode eliminates offset by allowing the controller to adapt by changing zero output
Integral action is provided by summing error over time, multiplying that sum by a gain and adding the result to the present controller output.