CCST Control System Design & Architecture 3

Question 1

Which document type formally defines the measurement ranges, alarm setpoints, and control modes for every instrument in a plant?

Accepted Answer

Instrument Index / Instrument Data Sheet

Answer

Instrument data sheets capture all engineering specifications for each tagged instrument, including range, calibration, alarm limits, and materials of construction.

Question 2

In control system design, what is 'control loop interaction' (coupling) and why is it a concern?

Accepted Answer

The unwanted influence one control loop has on another's controlled variable

Answer

Loop interaction occurs in multi-variable processes where adjusting one manipulated variable also affects another loop's controlled variable, complicating tuning and stability.

Question 3

A safety instrumented system (SIS) is designed to achieve SIL 2. Approximately what probability of failure on demand (PFD) range does SIL 2 require?

Accepted Answer

≥10⁻³ to <10⁻²

Answer

SIL 2 corresponds to a PFD range of 10⁻³ to 10⁻² (average probability of failure on demand between 1 in 1,000 and 1 in 100) per IEC 61508/61511.

Question 4

What is the difference between 'fail-safe' and 'fail-secure' in control system design?

Accepted Answer

Fail-safe moves to a safe process state; fail-secure maintains the last known state

Answer

Fail-safe drives the system to a predetermined safe condition (e.g., valve opens or closes), while fail-secure prioritizes maintaining the secured/locked state to prevent unauthorized access or process upset.

Question 5

In a feedforward control strategy, the feedforward signal is derived from:

Accepted Answer

A measured disturbance variable that is expected to affect the process

Answer

Feedforward control measures a disturbance before it affects the controlled variable and applies a corrective action predictively, rather than waiting for error to develop.

(CCST) Certified Control Systems Technician Practice Test

(CCST) Certified Control Systems Technician Practice Test

CCST Control System Design & Architecture 3