CPT Process Control & Automation 2

Question 1

In a cascade control system, which controller receives the setpoint from the operator?

Accepted Answer

Primary (master) controller

Answer

In cascade control, the operator sets the setpoint on the primary controller, which then outputs a setpoint to the secondary controller.

Question 2

What does the term 'offset' refer to in a proportional-only control loop?

Accepted Answer

A sustained steady-state error between setpoint and process variable

Answer

Proportional-only control produces a permanent offset (steady-state error) because it cannot eliminate error without integral action.

Question 3

Which valve characteristic provides an equal percentage change in flow for equal increments of valve travel?

Accepted Answer

Equal percentage

Answer

Equal percentage valves produce a constant percentage change in flow per unit of stem travel, making them suitable for processes with variable pressure drops.

Question 4

A control valve with an air-to-open (ATO) actuator will fail in which position on loss of instrument air?

Accepted Answer

Closed

Answer

An air-to-open valve requires air pressure to open; when air is lost, the spring returns the valve to the closed (fail-closed) position.

Question 5

What is the function of a positioner on a control valve?

Accepted Answer

To ensure the valve stem reaches and maintains the position commanded by the controller output

Answer

A valve positioner uses feedback from the stem position to ensure the valve accurately follows the controller output signal, overcoming friction and hysteresis.

(CPT) Certified Process Technician Practice Test

(CPT) Certified Process Technician Practice Test

CPT Process Control & Automation 2