Control Systems & Instrumentation Flashcards

When performing a process hazard analysis (PHA) for a control system, what does the acronym HAZOP stand for?

Answer: Hazard and Operability Study

HAZOP (Hazard and Operability Study) is a structured technique using guide words to identify potential hazards and operability problems in process designs.

In a split-range control scheme with two valves, how is the controller output typically divided?

Answer: One valve operates over 0-50% output and the other over 50-100% output

Split-range divides the controller output span between multiple actuators so each handles a different portion of the output range for wider process rangeability.

A resistance temperature detector (RTD) exhibits which fundamental electrical characteristic that makes it useful for temperature measurement?

Answer: Resistance increases predictably with increasing temperature (positive coefficient)

Platinum RTDs have a well-defined positive temperature coefficient of resistance, providing accurate and repeatable temperature measurement.

What is 'dead band' in a control instrument?

Answer: The range of input change that produces no change in output

Dead band is the range through which an input can change without producing any noticeable change in output, often caused by mechanical backlash or hysteresis.

In the Ziegler-Nichols closed-loop (ultimate gain) tuning method, which two parameters must be determined experimentally?

Answer: Ultimate gain (Ku) and ultimate period (Pu)

The Z-N closed-loop method requires finding the ultimate gain (Ku) that causes sustained oscillation and the resulting ultimate period (Pu) of oscillation.

Which type of level measurement technology is most suitable for interface level detection between two immiscible liquids of different densities?

Answer: Guided wave radar (GWR) transmitter

Guided wave radar can detect two distinct reflection points along the probe — one at the upper liquid surface and one at the liquid-liquid interface.

What is the significance of the 'process gain' (Kp) in control loop analysis?

Answer: It is the ratio of change in process output to change in controller output at steady state

Process gain (Kp) quantifies how much the process output changes per unit change in controller output at steady state, critical for proper controller tuning.