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 is the primary purpose of a distributed control system (DCS) compared to a standalone controller?
Answer: To distribute control across multiple processors while providing centralized monitoring
A DCS distributes control functions across multiple controllers while allowing operators to monitor and manage the entire plant from centralized operator stations.
In a programmable logic controller (PLC), what is a 'scan cycle'?
Answer: The sequential process of reading inputs, executing logic, and updating outputs
A PLC scan cycle consists of reading all input states, executing the control program logic, and then writing the results to all outputs, repeated continuously.
What does 'split-range control' involve?
Answer: Sending a single controller output to two or more final control elements that operate in sequence
Split-range control sends one controller output signal to multiple valves that each operate over a different portion of the output range (e.g., 0–50% and 50–100%).
Which term describes the change in process variable per unit change in controller output, expressed as a ratio?
Answer: Process gain
Process gain is the ratio of the change in the controlled variable to the change in the manipulated variable, characterizing how sensitive the process is to control action.
A thermocouple produces a signal based on which principle?
Answer: Voltage generated at the junction of two dissimilar metals
Thermocouples operate on the Seebeck effect, where a voltage is produced at the junction of two dissimilar metals proportional to the temperature difference.
What is 'dead band' in the context of a control system?
Answer: A range of input values over which no output change occurs
Dead band is a range of the input (or error) signal within which the controller takes no corrective action, which can cause limit cycling or persistent offset.
Which safety instrumented system (SIS) term describes the probability that a safety function will fail to operate on demand?
Answer: Probability of failure on demand (PFD)
Probability of failure on demand (PFD) quantifies the likelihood that a safety system will not perform its intended protective function when a hazardous event occurs.