Process Control Systems & Automation Flashcards
7 cards from real CPAT 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 Systems & Automation flashcards as text
What does the acronym PID stand for in a PID controller used in process automation?
Answer: Proportional-Integral-Derivative
PID stands for Proportional-Integral-Derivative, referring to the three mathematical terms used to calculate the controller output.
In a feedback control loop, what signal does the controller compare to the setpoint to determine corrective action?
Answer: The process variable (PV)
The controller compares the measured process variable (PV) to the setpoint to calculate the error and determine the required corrective output.
Which control action in a PID controller is responsible for eliminating steady-state offset (residual error)?
Answer: Integral action
Integral action accumulates the error over time and continuously adjusts the output until the error is driven to zero, eliminating steady-state offset.
What is the primary purpose of derivative action in a PID controller?
Answer: Respond to the rate of change of the error to dampen oscillations
Derivative action responds to the rate at which the error is changing, providing a dampening effect that reduces overshoot and oscillations.
In a simple process control loop, what is the role of the final control element?
Answer: Receive the controller output and physically alter the process
The final control element (typically a control valve or variable-speed drive) receives the controller's output signal and physically changes the manipulated variable to influence the process.
What is 'cascade control' in process automation?
Answer: A control strategy where two controllers are connected, with the output of the primary controller setting the setpoint of the secondary controller
Cascade control links two controllers so that the outer (primary) controller's output becomes the setpoint for the inner (secondary) controller, improving response to disturbances in the inner loop.
Which of the following best describes a 'process variable' (PV) in a control loop?
Answer: The measured value of the parameter being controlled
The process variable is the actual measured value of the parameter under control (e.g., temperature, pressure, or flow) as detected by the sensor/transmitter.