Data Interpretation & Analysis Flashcards

A maintenance technician reviews a control chart tracking hydraulic pressure (PSI) over an 8-hour shift. The process mean is 350 PSI with control limits at 320 PSI (LCL) and 380 PSI (UCL). The last 7 consecutive readings are: 355, 358, 362, 367, 371, 374, 378. Which condition does this data pattern indicate?

Answer: A run rule violation indicating a non-random upward trend requiring investigation

Even though all seven readings fall within the control limits, seven consecutive points trending in one direction (all increasing) triggers a run rule violation — a recognized statistical signal that the process is shifting. This non-random pattern indicates a special cause (e.g., a gradual leak, temperature rise, or valve wear) that requires investigation before the process goes out of control.

A vibration analysis report shows three frequency peaks for a centrifugal pump: 29.5 Hz at 0.18 in/s, 59 Hz at 0.42 in/s, and 118 Hz at 0.11 in/s. The pump runs at 1770 RPM and has a 6-vane impeller. Which conclusion is BEST supported by this data?

Answer: Blade pass frequency energy is dominant, suggesting impeller-related turbulence or recirculation

The running speed (1× RPM) is 1770 ÷ 60 = 29.5 Hz, and the blade pass frequency (BPF) = 29.5 × 6 vanes = 177 Hz — however, 59 Hz (2×) being the dominant peak is characteristic of hydraulic instability such as recirculation or cavitation amplified at 2× running speed, a known indicator of impeller-related flow issues. The highest amplitude peak at 2× running speed rather than 1× or BPF points to impeller/hydraulic causes.

A plant engineer compares motor efficiency data for four identical 50 HP motors running at different load percentages. The table shows: Motor A at 50% load = 91.2% efficiency; Motor B at 75% load = 93.8% efficiency; Motor C at 100% load = 93.1% efficiency; Motor D at 115% load = 91.6% efficiency. Which interpretation is correct?

Answer: Motor B produces peak efficiency, confirming that induction motors are typically most efficient between 70–80% of rated load

Induction motors reach peak efficiency between approximately 70–80% of full load — this is a well-established characteristic of their design. The data confirms this: Motor B at 75% load shows the highest efficiency (93.8%). Motor A at 50% load is undersized for its application (wasting iron losses), Motor C is slightly past peak, and Motor D is overloaded, which risks overheating and insulation degradation regardless of its momentary efficiency figure.

An oil analysis report for a gearbox shows these trend values over four consecutive months — Viscosity (cSt at 40°C): 218, 224, 231, 247; Iron (ppm): 38, 41, 44, 48; Silicon (ppm): 4, 12, 28, 61. Copper (ppm) remains stable at 6 ppm throughout. Which interpretation is MOST accurate?

Answer: The exponential rise in silicon is the most critical finding, indicating a failed air breather or seal allowing contamination

Silicon ppm that roughly doubles each month (4→12→28→61) is an exponential trend — the hallmark of an ingression contamination path such as a failed breather, damaged seal, or compromised gasket. Abrasive silica contamination then accelerates iron wear (the rising iron trend is secondary). Copper stability only rules out brass/bronze component wear, not the contamination source. The exponential silicon curve demands immediate investigation — not a future oil change — because abrasive ingression causes rapidly accelerating damage.

A technician reads a Pareto chart of maintenance work orders for one quarter. The categories and percentages are: Lubrication failures 38%, Electrical faults 27%, Misalignment 14%, Operator error 11%, and Other 10%. Management wants to reduce total downtime by 50% with the minimum number of corrective programs. Which strategy does the data support?

Answer: Target lubrication failures and electrical faults together, as they account for 65% of work orders

The Pareto principle (80/20 rule) dictates focusing on the vital few causes. Lubrication (38%) and electrical faults (27%) together represent 65% of all work orders. Addressing only lubrication leaves 62% of downtime untouched — insufficient to hit a 50% reduction goal. Combining both programs targets the two highest contributors with just two focused initiatives, yielding the greatest return with minimum corrective programs — which is exactly what management specified.

A power quality meter logs these RMS voltage readings across 24 hours on a 480 V nominal system: 6 AM–2 PM average 483 V, 2 PM–6 PM average 471 V, 6 PM–10 PM average 468 V, 10 PM–6 AM average 487 V. ANSI C84.1 standard specifies a service voltage range of ±5% of nominal (456–504 V). Which analysis is correct?

Answer: All readings are within ANSI limits; no action is required

The ANSI C84.1 ±5% tolerance on 480 V yields a range of 456 V (480 × 0.95) to 504 V (480 × 1.05). All four readings — 483 V, 471 V, 468 V, and 487 V — fall within this window. The 468 V reading may appear low but is still above the 456 V lower limit. A common mistake is applying ±5% as ±24 V from the meter reading rather than from the nominal voltage, or misremembering the standard as ±3%. No ANSI violation exists in this dataset.