TOEIC Link Vocabulary — Vibration Analysis and Bearing Fault Diagnosis Cluster

Vibration analysis reports are a rich source of TOEIC Link reading passages because they pair a compact technical vocabulary with a diagnostic narrative — a symptom is measured, a spectrum is interpreted, a fault is named, and a maintenance action is recommended. The reading questions almost always target the interpretation step, where the report moves from a measured value to a named fault, so a candidate who can read the diagnostic vocabulary fluently reaches the answer sentence far faster than one who is still decoding the terminology. This cluster organizes the vocabulary the way the reports use it, and closes with the report frames that carry the questions.

Vibration analysis is a condition-monitoring method for rotating machinery — pumps, motors, fans, compressors, gearboxes, and turbines — in which vibration is measured, converted to a frequency spectrum, and interpreted to detect developing faults before they cause failure. Because faults appear as energy at characteristic frequencies, the vocabulary of frequency dominates the passages, and learning it as a set of related terms is far more efficient than meeting each word cold.

Measurement vocabulary

The measured quantity is described by three interchangeable-but-distinct terms that passages use precisely: displacement (how far the part moves, used at low frequency), velocity (how fast it moves, the most common overall-severity measure), and acceleration (the rate of change of velocity, used to find high-frequency bearing and gear faults). A passage that reports "overall velocity in mm/s RMS" is giving a severity figure; a passage that shifts to "acceleration envelope" is signalling bearing analysis.

Core measurement terms to lock in as a group: amplitude (the size of the vibration), RMS (root-mean-square, the standard averaging method for severity), peak and peak-to-peak, overall level (a single number summarizing total vibration energy), baseline (the reference reading a healthy machine produced), and alarm and trip thresholds. The severity judgment in almost every passage is a comparison of the overall level against the baseline or the alarm threshold, so these are the words the question stem will echo.

Spectrum and defect-frequency vocabulary

The interpretive core of the report is the frequency spectrum — usually called the FFT spectrum after the fast-Fourier-transform that produces it — which decomposes the vibration into its component frequencies. Faults appear at characteristic frequencies expressed as multiples of running speed (also called 1×, the once-per-revolution frequency, or turning speed).

The fault-frequency vocabulary maps directly to fault types, and learning the pairing is the highest-value study move: unbalance appears at 1×; misalignment appears at 2× (and sometimes 1× axially); mechanical looseness produces a series of harmonics (integer multiples) and sometimes sub-harmonics (half-order); a bent shaft, a broken rotor bar, and blade-pass phenomena each have their own signature. Bearing faults appear at non-synchronous bearing defect frequencies — the BPFO (ball pass frequency outer race), BPFI (ball pass frequency inner race), BSF (ball spin frequency), and FTF (fundamental train frequency / cage frequency). Gear faults appear at gear mesh frequency (GMF) with sidebands spaced at running speed.

Two terms recur specifically in bearing diagnosis and are worth isolating: envelope analysis (also demodulation), the technique that pulls the repetitive bearing impacts out of the broadband noise, and crest factor, the ratio of peak to RMS that rises early in bearing degradation. When a passage introduces "envelope spectrum" or "high crest factor," the diagnosis is heading toward a bearing fault.

Fault-progression vocabulary

Bearing faults follow a recognized progression that the reports narrate, and the vocabulary of that progression is testable: incipient (earliest, detectable only in ultrasonic and acceleration bands), developing, advanced, and severe or imminent failure. Associated action words scale with the stage — monitor, trend, schedule replacement, expedite, and remove from service. The report's recommendation sentence is chosen directly from the fault stage, so locating the stage word usually locates the recommended action. This progression vocabulary overlaps closely with the broader vibration analysis and rotating-equipment condition monitoring services cluster and connects to the actuator-diagnostics domain in the valve actuator stroke and diagnostic testing services cluster.

Report-language patterns that carry the questions

The passages reuse four frames. The measurement frame states the reading: "Overall velocity at the outboard bearing rose from a baseline of 2.1 mm/s to 6.8 mm/s RMS." The interpretation frame names the pattern: "The envelope spectrum shows a clear BPFO peak with harmonics, indicating an outer-race defect." The stage frame places it on the progression: "The defect is assessed as developing rather than incipient." The recommendation frame prescribes: "It is recommended that the bearing be replaced at the next scheduled outage and that vibration be trended weekly until then."

Inference questions cluster on the interpretation and stage frames, because those are where the analyst exercises judgment rather than reporting a number. Train yourself to find the fault-name word — unbalance, misalignment, looseness, outer-race, inner-race — and read the sentence around it first, because it links the measurement to the recommendation that the question is usually asking about.

A one-week consolidation drill

Twenty minutes a day. Days one and two: write the fault-to-frequency pairings from memory (1× unbalance, 2× misalignment, harmonics looseness, defect frequencies for bearings). Days three and four: define each bearing defect frequency and the two bearing-specific techniques (envelope, crest factor) in one sentence each. Days five and six: take any diagnostic sentence and label its report frame. Day seven: time yourself on two passages, locating the fault-name word before reading its sentence. The goal is to make the diagnostic vocabulary recognition-fast, so the reading questions become a matter of locating a known pattern rather than decoding an unfamiliar one.