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
When a process control loop exhibits 'hunting' or cycling behavior, what is the most likely cause?
Answer: Controller gain or integral action is too aggressive
Hunting or sustained cycling typically results from excessive proportional gain or too much integral action, causing the controller to overcorrect continuously.
What is the purpose of 'anti-reset windup' circuitry in a PID controller?
Answer: To limit integral accumulation when the controller output is at its limits
Anti-reset windup circuitry stops the integral term from accumulating when the controller output is saturated, preventing delayed or excessive response when the output returns to normal range.
In process instrumentation, a 'transmitter' differs from a simple sensor in that a transmitter:
Answer: Conditions and converts the measured signal to a standardized output such as 4–20 mA
A transmitter converts the raw sensor signal into a standardized, scalable output (such as 4–20 mA or digital fieldbus) suitable for transmission to a control system.
What does a 'process flow diagram' (PFD) show that a 'piping and instrumentation diagram' (P&ID) typically omits?
Answer: Major equipment, mass/energy balances, and overall process flow
A PFD shows the overall process flow, major equipment, and material/energy balances, while a P&ID provides detailed piping, instrumentation, and control information.
Which type of control action is most appropriate for a process that requires very tight control with no steady-state error and exhibits minimal noise?
Answer: Proportional-integral (PI)
PI control eliminates steady-state offset through integral action and is appropriate for most process loops; derivative is avoided when signal noise is a concern.
In hazardous area classification, what does a Zone 1 designation indicate under IEC standards?
Answer: An area where an explosive gas atmosphere is likely to occur during normal operation
IEC Zone 1 designates an area where an explosive atmosphere in the form of a cloud of flammable gas is likely to exist during normal operation periodically.
What is the primary function of a 'ratio controller' in process control?
Answer: To maintain the ratio of two process variables at a desired value
A ratio controller maintains a fixed ratio between two process streams (e.g., fuel-to-air ratio in a combustion system) by adjusting one stream proportionally to the other.