CCST Process Optimization & Performance Tuning Flashcards
6 cards from real CCST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CCST Process Optimization & Performance Tuning flashcards as text
In a cascade control configuration, which controller directly manipulates the final control element (e.g., control valve)?
Answer: Secondary (inner) controller
In cascade control, the secondary (inner) controller receives its setpoint from the primary controller and directly positions the final control element.
What is the main advantage of feedforward control compared to feedback control in a process loop?
Answer: Feedforward acts on measured disturbances before they affect the process variable, reducing disturbance response time
Feedforward control measures a known disturbance and adjusts the controller output proactively, compensating for the disturbance before it can affect the controlled variable.
A CCST technician is analyzing a process trend and observes a sinusoidal oscillation with a period equal to the loop scan time. What is the most likely cause?
Answer: Aliasing due to the scan rate being too slow relative to process dynamics
Aliasing occurs when the control system scan rate is slower than twice the frequency of a process oscillation (violating Nyquist), causing the oscillation to appear at the wrong frequency in trends.
In process optimization, what does the term 'process capability index (Cpk)' quantify?
Answer: How well a process performs relative to its specification limits, accounting for both spread and centering
Cpk measures how centered and how tightly controlled a process is relative to its upper and lower specification limits — higher Cpk means fewer defects.
What is the purpose of a 'bump test' (step test) performed on a control loop that is switched to manual mode?
Answer: To identify process dynamics such as gain, dead time, and time constant for tuning calculations
A bump test applies a step change to the controller output in manual mode and records the process variable response to identify the process model parameters needed for tuning.
Which statistical process control tool is used to determine whether process variability is due to common cause or special cause variation?
Answer: Control chart (Shewhart chart)
Control charts plot process data over time with statistical control limits, allowing technicians to distinguish natural common-cause variation from abnormal special-cause events requiring investigation.