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Scenario
You are the on-call engineer for a hydrogen compressor skid. The control system has five sensors arranged in a serial telemetry chain. Each sensor reports its own reading and passes all upstream readings downstream unchanged.
If exactly one sensor is faulty, it reports an incorrect value for its own measurement — but faithfully relays whatever the sensors upstream of it reported. Sensors downstream of a faulty one receive and relay the corrupted data without modification.
At 03:14 the master controller logs a warning. You pull the telemetry snapshot below. Exactly one sensor is malfunctioning. Your job: identify which one, what it actually reads, and determine the true system state.
Telemetry snapshot
Sensor 1 — Inlet pressure Reported: 12.4 bar Nominal range: 11–14 bar Note: S1 relays no upstream data. Physical constraint: inlet pressure must always be lower than stage-1 discharge pressure.
Sensor 2 — Stage-1 discharge pressure Reported: 9.1 bar Nominal range: 28–35 bar Note: S2 relays S1 = 12.4 bar. Compression ratio at this stage should be approximately 2.4–2.6×.
Sensor 3 — Inter-stage temperature Reported: 148 °C Nominal range: 130–160 °C Note: S3 relays S1 = 12.4 bar, S2 = 9.1 bar. Temperature is consistent with gas compressed to approximately 9 bar from 12 bar.
Sensor 4 — Stage-2 discharge pressure Reported: 87.3 bar Nominal range: 70–90 bar Note: S4 relays S1 = 12.4 bar, S2 = 9.1 bar, S3 = 148 °C. Compression ratio from S2 reading: 9.6×.
Sensor 5 — Final outlet flow rate Reported: 340 Nm³/h Nominal range: 310–370 Nm³/h Note: S5 relays all upstream values unchanged. Flow is within range for the reported outlet conditions.
Questions
- Which single sensor is faulty?
- What physical law or engineering constraint exposes the contradiction?
- What is the sensor's true reading, given that all other sensors are accurate?
- Bonus: Is the system in a safe state, or should you trigger a shutdown?
Admin note: This logic puzzle was created with the help of generative AI. Give us your feelings or criticisms of this in the comments below.
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Re: Sensors and Senseless (June 2026 Challenge Question)
