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
A ratio control system is used in a combustion process. What is being maintained by the ratio controller?
Answer: A defined proportion between two process streams, such as fuel and air flow
A ratio controller maintains a fixed proportion between two streams (e.g., fuel-to-air ratio) so that as one stream changes, the other is automatically adjusted to maintain the correct ratio.
When performing a control loop performance assessment, what does a high 'Harris Index' (close to 1.0) indicate?
Answer: The loop is operating near its minimum variance (theoretical best) performance
The Harris Index compares actual loop variability to the minimum achievable variance (limited by dead time); a value near 1.0 indicates the loop is performing near its theoretical optimum.
In a heat exchanger control loop where the process has a strong nonlinear gain, what control technique is used to maintain consistent loop performance across the operating range?
Answer: Gain scheduling
Gain scheduling adjusts controller tuning parameters as a function of operating point (e.g., valve position or process variable range) to compensate for process nonlinearity.
What is the purpose of a 'split-range' control strategy in a process heating/cooling system?
Answer: To drive two or more final control elements in sequence from a single controller output signal
Split-range control maps different portions of the controller output (e.g., 0–50% and 50–100%) to separate control elements, such as a heating valve and a cooling valve, from a single controller.
A CCST technician observes that a flow control loop is very difficult to tune because small valve movements cause large flow changes. What process characteristic is this?
Answer: High process gain
High process gain means the process variable (flow) changes significantly for a small change in controller output (valve position), requiring a smaller proportional gain to maintain stability.
In model predictive control (MPC), what is the function of the 'prediction horizon'?
Answer: The time window over which future process behavior is predicted using the process model to optimize controller moves
The prediction horizon defines how far into the future the MPC algorithm projects the process response to candidate control moves, allowing it to optimize actions while respecting future constraints.