SACA Cyber-Physical Systems 5 — Questions and Answers
Question 1: Which design principle helps CPS maintain safe operation even when one or more components fail?
- Single point of control
- Fail-safe design with graceful degradation (Correct answer)
- Maximum throughput optimization
- Centralized data processing
Correct answer: Fail-safe design with graceful degradation
Fail-safe design with graceful degradation ensures a CPS moves to a safe, reduced-functionality state rather than failing catastrophically.
Question 2: In the NIST CPS Framework, which domain focuses on trustworthiness properties such as safety, security, privacy, and reliability?
- Functional domain
- Business domain
- Trustworthiness domain (Correct answer)
- Physical domain
Correct answer: Trustworthiness domain
The NIST CPS Framework's trustworthiness domain explicitly addresses safety, security, privacy, reliability, and resilience as cross-cutting concerns.
Question 3: What is 'sensor fusion' and why is it valuable in CPS?
- Physically combining multiple sensors into one unit to reduce cost
- Combining data from multiple sensors to produce more accurate and reliable information than any single sensor provides (Correct answer)
- Using one master sensor to validate all other sensors
- Encrypting sensor data before transmission
Correct answer: Combining data from multiple sensors to produce more accurate and reliable information than any single sensor provides
Sensor fusion merges inputs from multiple sensors to compensate for individual limitations and deliver higher-accuracy system state estimates.
Question 4: An autonomous vehicle CPS receives conflicting signals from its LIDAR and camera sensors. What control strategy should BEST resolve this?
- Always prioritize camera data over LIDAR
- Use a predefined arbitration algorithm that weights sensor confidence and applies sensor fusion (Correct answer)
- Halt the vehicle immediately and await manual intervention
- Discard both readings and use GPS only
Correct answer: Use a predefined arbitration algorithm that weights sensor confidence and applies sensor fusion
A confidence-weighted sensor fusion and arbitration algorithm resolves conflicts systematically while maintaining safe operation.
Question 5: What is the significance of 'latency' in feedback control loops within CPS?
- High latency improves control precision
- Excessive latency can cause instability or unsafe behavior because control actions arrive too late to correct deviations (Correct answer)
- Latency only affects data logging, not control
- Latency is irrelevant if the actuator is fast enough
Correct answer: Excessive latency can cause instability or unsafe behavior because control actions arrive too late to correct deviations
In closed-loop CPS control, delays beyond the system's tolerance can cause oscillation, instability, or failure to correct unsafe conditions in time.
Question 6: Which of the following BEST describes 'edge computing' in a CPS context?
- Moving all computation to a central cloud data center
- Processing data close to the physical devices to reduce latency and bandwidth usage (Correct answer)
- Using only on-device storage without network connectivity
- Delegating all control decisions to human operators
Correct answer: Processing data close to the physical devices to reduce latency and bandwidth usage
Edge computing processes data near the source—on gateways or local servers—enabling real-time CPS responses without cloud round-trip delays.
Question 7: In IEC 62443, what is the purpose of defining 'Security Levels' (SL) for industrial CPS?
- To rank network speed tiers for industrial equipment
- To categorize the robustness of security countermeasures required based on the consequence and likelihood of attack (Correct answer)
- To classify physical hazard zones in a facility
- To set pricing tiers for cybersecurity software licenses
Correct answer: To categorize the robustness of security countermeasures required based on the consequence and likelihood of attack
IEC 62443 Security Levels define the required strength of security measures based on the risk profile—higher consequences demand higher security levels.
SACA Cyber-Physical Systems 5
Which design principle helps CPS maintain safe operation even when one or more components fail?