Advanced Techniques & Methods Flashcards

Which advanced process control (APC) technique is most appropriate when the process has explicit operating constraints that must not be violated?

Answer: Model Predictive Control (MPC)

MPC inherently handles hard and soft constraints on inputs, outputs, and rate-of-change through its constrained optimization formulation.

A process with a Right Half Plane (RHP) zero in its transfer function will initially respond in which direction when a step change is applied to its input?

Answer: In the opposite direction to the final steady-state change (inverse response)

An RHP zero causes inverse response: the process output first moves opposite to its eventual steady-state direction, severely limiting achievable closed-loop bandwidth.

The LMTD (Log Mean Temperature Difference) correction factor F in a shell-and-tube heat exchanger design accounts for:

Answer: Deviation from pure countercurrent flow due to multiple passes

The F factor corrects the LMTD calculated assuming pure countercurrent flow to account for the mixed flow patterns in multi-pass exchangers.

In process hazard analysis, what does LOPA (Layer of Protection Analysis) quantify?

Answer: Whether existing independent protection layers are sufficient to reduce risk to a tolerable level

LOPA computes the frequency of a hazardous event after accounting for the probability of failure on demand (PFD) of each independent protection layer.

ISA-5.1 specifies that a valve positioner should be symbolized on a P&ID as:

Answer: A separate instrument bubble connected to the valve actuator

Per ISA-5.1, accessory devices such as positioners are represented as separate instrument bubbles tagged accordingly and connected to the primary final control element symbol.

When performing a relay feedback test (Åström-Hägglund) to auto-tune a PID controller, the two values extracted are:

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

The relay test induces sustained oscillation; from the relay amplitude and resulting output oscillation amplitude and period, Ku and Pu are calculated and used with Ziegler-Nichols formulas.

In fieldbus and digital instrumentation, the term 'Function Block' (as used in FOUNDATION Fieldbus) refers to:

Answer: A software module that executes a defined control or I/O algorithm within a device

FOUNDATION Fieldbus function blocks (e.g., AI, AO, PID) are standardized software objects that execute algorithms and communicate parameters across the fieldbus network.