Process Control & Automation Flashcards
7 cards from real CPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Process Control & Automation flashcards as text
What effect does increasing the derivative time (Td) have on a PID controller's response?
Answer: Increases the controller's reaction to rapidly changing errors
Increasing derivative time makes the controller more sensitive to the rate of change of the error, providing anticipatory action and damping fast-changing disturbances.
In the ISA standard for process control loops, what does the letter 'C' represent in a tag such as 'TIC-101'?
Answer: Controller
Per ISA 5.1, the letter 'C' in an instrument tag stands for Controller; TIC-101 is therefore a Temperature Indicating Controller.
Which type of process displays a 'self-regulating' behavior when a step change is applied to the manipulated variable?
Answer: Self-regulating process
A self-regulating process naturally reaches a new steady-state after a disturbance without controller action, because internal process dynamics balance the change.
What is the main advantage of using a 4–20 mA current signal over a voltage signal for transmitting process data?
Answer: Current signals are immune to voltage drops caused by wire resistance
A 4–20 mA current loop is unaffected by the resistance of the wiring because the same current flows throughout the loop regardless of line resistance.
In a control valve, what is the 'rangeability' specification?
Answer: The ratio of maximum to minimum controllable flow
Rangeability is the ratio of the maximum to minimum controllable flow rate within which the valve maintains its stated flow characteristic.
Which Ziegler-Nichols tuning method requires bringing the loop to sustained oscillation by increasing proportional gain alone?
Answer: Closed-loop (ultimate gain) method
The Ziegler-Nichols closed-loop method finds the ultimate gain (Ku) and ultimate period (Pu) by increasing proportional gain until the loop oscillates continuously.
What is the role of a FOUNDATION Fieldbus or PROFIBUS device in a modern process plant?
Answer: To enable two-way digital communication between field devices and the control system over a single pair of wires
Fieldbus protocols such as FOUNDATION Fieldbus and PROFIBUS allow multiple field devices to communicate digitally on a single cable, enabling diagnostics, configuration, and process data transmission.