Process Control and Instrumentation Flashcards
6 cards from real Plant Operator Selection System Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Process Control and Instrumentation flashcards as text
In process control, 'cascade control' means:
Answer: Two controllers where the output of the primary sets the setpoint of the secondary
In cascade control, the primary (master) controller's output drives the setpoint of the secondary (slave) controller, improving disturbance rejection.
A Safety Instrumented System (SIS) is designed to:
Answer: Automatically bring the process to a safe state when a dangerous condition is detected
The SIS is an independent layer of protection that takes automatic action (shutdown, depressurization, etc.) when the BPCS fails to prevent a hazardous condition.
Which instrument tag designation on a P&ID indicates a flow controller?
Answer: FC
In ISA instrument tag notation, 'F' is the measured variable (flow) and 'C' is the function (controller), making FC a flow controller.
Dead band in a control instrument refers to:
Answer: The range over which input changes cause no output response
Dead band is the input change range that produces no detectable change in output, often caused by mechanical friction or hysteresis in final control elements.
When a process control loop is placed in 'manual' mode by the operator, it means:
Answer: The operator directly sets the controller output and the setpoint is ignored
In manual mode, the operator fixes the controller output at a chosen value while the automatic setpoint-based calculation is suspended.
A 4-20 mA current signal is used in process instrumentation primarily because:
Answer: It is less susceptible to electrical noise and a live zero detects broken wires
The 4-20 mA standard's live zero (4 mA = 0%) allows wire breaks (0 mA) to be distinguished from a valid zero-range reading, and current signals resist voltage noise pickup.
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