CCST CCST Process Optimization & Performance Tuning 2

Question 1

In a cascade control configuration, which controller directly manipulates the final control element (e.g., control valve)?

Accepted Answer

Secondary (inner) controller

Answer

In cascade control, the secondary (inner) controller receives its setpoint from the primary controller and directly positions the final control element.

Question 2

What is the main advantage of feedforward control compared to feedback control in a process loop?

Accepted Answer

Feedforward acts on measured disturbances before they affect the process variable, reducing disturbance response time

Answer

Feedforward control measures a known disturbance and adjusts the controller output proactively, compensating for the disturbance before it can affect the controlled variable.

Question 3

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?

Accepted Answer

Aliasing due to the scan rate being too slow relative to process dynamics

Answer

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.

Question 4

In process optimization, what does the term 'process capability index (Cpk)' quantify?

Accepted Answer

How well a process performs relative to its specification limits, accounting for both spread and centering

Answer

Cpk measures how centered and how tightly controlled a process is relative to its upper and lower specification limits — higher Cpk means fewer defects.

Question 5

What is the purpose of a 'bump test' (step test) performed on a control loop that is switched to manual mode?

Accepted Answer

To identify process dynamics such as gain, dead time, and time constant for tuning calculations

Answer

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.

(CCST) Certified Control Systems Technician Practice Test

(CCST) Certified Control Systems Technician Practice Test

CCST CCST Process Optimization & Performance Tuning 2