Instrumentation & Process Control Flashcards
7 cards from real CCST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Instrumentation & Process Control flashcards as text
A cascade control system consists of two controllers. Which controller's output directly manipulates the final control element?
Answer: Secondary (slave) controller
In cascade control the secondary (slave) controller receives its setpoint from the primary and directly outputs to the final control element such as a valve.
Which sensor type operates on the principle of electrical resistance change proportional to mechanical strain?
Answer: Strain gauge
A strain gauge changes its electrical resistance when deformed, and the resistance change is proportional to the applied strain.
The gain of a proportional controller is increased. What is the expected effect on steady-state offset for a step load disturbance?
Answer: Offset decreases but is not eliminated
Higher proportional gain reduces offset because the controller produces a larger corrective output per unit of error, but proportional-only control can never fully eliminate steady-state offset.
A Coriolis flowmeter measures flow based on which physical principle?
Answer: Inertial force caused by mass flow through vibrating tubes
Coriolis meters measure the twist (phase shift) in vibrating tubes caused by the inertial Coriolis force, which is directly proportional to mass flow rate.
What does 'turndown ratio' describe in the context of a flowmeter?
Answer: Ratio of maximum to minimum measurable flow with acceptable accuracy
Turndown ratio (also called rangeability) expresses the ratio of the maximum to minimum flow rate within which the meter meets its accuracy specification.
In a split-range control scheme, two control valves are operated by a single controller output. How is the output typically split?
Answer: One valve operates over 4-12 mA and the other over 12-20 mA
In classic split ranging, the controller output is divided so valve A strokes over the lower half (4-12 mA) and valve B strokes over the upper half (12-20 mA) of the signal range.
A level transmitter using a displacer element measures level based on which principle?
Answer: Buoyancy force change on a submerged displacer
A displacer level transmitter senses the change in buoyancy force as liquid level rises or falls around the suspended displacer, converting force change to a level signal.