Test 2 Flashcards
Controller Tuning
The process of determining the tuning coefficients for the PID controller to obtain a desired controller response to process disturbances.
Decay Ratio
Measure of how quickly an overshoot decays from one oscillation to the next as the controller brings the process to the setpoints.
Overshoot
The change of a PV that exceeds the upper deadband value when there is a disturbance to a system.
Deadtime
change is made to first sensed.
Rise time
The length of time required for a PV to cross the ultimate value after a step input change, such as a setpoint change.
Dynamic response time
The length of time required for a PV to remain within 5% of its ultimate value following a step input change.
Gain Margin
The factor by which controller gain may be increased before instability occurs, and therefore is a measure of relative stability.
Self-tuning controller
Controller that has built-in algorithms or pattern recognition techniques that periodically test the process and make changes to the controller tuning settings while the process is operating.
Stand-alone controller
Controller that has its power supplies, input signal processing, controller functions, output signals, and displays contained in the same case.
Pretuning checks
- Ensure that the controller action is selected correctly. (direct or reverse)
- Determine which controller functions are needed for the process. (Integral, Derivative, or Proportional)
- Determine the initial tuning values that are to be used for the chosen controller functions. (Initial values)
Setpoint step change method
Manual tuning method that consists of making small changes in the setpoint and observing the responses.
Setpoint step change method steps
- Controller must be in auto mode and the measurement should be steady.
- Adjust proportional gain, integral time, and derivative function accordingly.
Tuning map method
Procedure for controller tuning that compares process curves to one of numerous typical closed loop response curves.
Ziegler-Nichols Tuning Method
Variation of one quarter wave decay.
Ziegler-Nichols closed loop tuning
Tuning a controller by increasing the gain until the system cycles at the point of instability.
Ziegler-Nichols open loop tuning
Tuning a controller based on open loop response to a step input.