CPT Process Control & Automation 4

Question 1

What effect does increasing the derivative time (Td) have on a PID controller's response?

Accepted Answer

Increases the controller's reaction to rapidly changing errors

Answer

Increasing derivative time makes the controller more sensitive to the rate of change of the error, providing anticipatory action and damping fast-changing disturbances.

Question 2

In the ISA standard for process control loops, what does the letter 'C' represent in a tag such as 'TIC-101'?

Accepted Answer

Controller

Answer

Per ISA 5.1, the letter 'C' in an instrument tag stands for Controller; TIC-101 is therefore a Temperature Indicating Controller.

Question 3

Which type of process displays a 'self-regulating' behavior when a step change is applied to the manipulated variable?

Accepted Answer

Self-regulating process

Answer

A self-regulating process naturally reaches a new steady-state after a disturbance without controller action, because internal process dynamics balance the change.

Question 4

What is the main advantage of using a 4–20 mA current signal over a voltage signal for transmitting process data?

Accepted Answer

Current signals are immune to voltage drops caused by wire resistance

Answer

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.

Question 5

In a control valve, what is the 'rangeability' specification?

Accepted Answer

The ratio of maximum to minimum controllable flow

Answer

Rangeability is the ratio of the maximum to minimum controllable flow rate within which the valve maintains its stated flow characteristic.

(CPT) Certified Process Technician Practice Test

(CPT) Certified Process Technician Practice Test

CPT Process Control & Automation 4