Regarding industrial automation, which statement best reflects recommended design and lifecycle properties of computer-based controllers?

Introduction / Context:
Computer-based controllers are used across process and discrete manufacturing. The design philosophy influences maintainability, scalability, downtime risk, and ability to implement improvements. This question checks whether you understand why modularity and flexibility are desirable traits.

Given Data / Assumptions:

• Controllers may need reconfiguration for new products or recipes.
• Hardware and software updates occur over time.
• Plants aim to reduce mean time to repair and changeover times.

Concept / Approach:
Modularity partitions a system into replaceable units (I/O cards, communication modules, function blocks), enabling localized changes. Flexibility refers to the controller's capability to adapt via parameterization, reprogramming, and extensible I/O without complete redesign.

Step-by-Step Solution:

Verification / Alternative check:
Vendor-neutral standards (e.g., IEC 61131-3 function blocks) and modular I/O backplanes exemplify modular, flexible controller ecosystems that support rapid changeovers and incremental upgrades.

Why Other Options Are Wrong:

• should be built in a modular fashion wherever possible: incomplete because it omits flexibility.
• are very difficult to change: conflicts with real-world reprogramming and modular swaps.
• are very flexible: incomplete; does not emphasize modular design principle.
• None of the above: incorrect because the combined statement is appropriate.

Common Pitfalls:
Equating flexibility with ad-hoc changes without proper versioning, and overlooking the role of standardized modules and documentation in safe modifications.

Final Answer:
should be built in a modular fashion wherever possible and are very flexible