How to Measure Motor Vibration With Your Phone

An electric motor is the most common machine you will ever put a vibration meter on — and your phone can do it. Using the built-in accelerometer, you can read a motor’s overall vibration in mm/s, spot the two most common faults (imbalance and misalignment) from the frequency spectrum, and track the motor’s health over time. It takes about a minute and no extra hardware.

This guide is motor-specific: where exactly to measure on a motor, what your reading is telling you about the motor’s condition, and what a phone can and cannot catch. If you want the general measurement technique that applies to any machine, see our full walkthrough on measuring vibration with a phone — here we focus on motors. To follow along, grab the free Vibration Detector Sensor app.

Check your motor in under a minute

Press your phone to the motor’s bearing housing and read live RMS velocity in mm/s, plus the spectrum that reveals imbalance and misalignment.

► Download on the App Store  |  See how it works →

Why measure motor vibration?

Vibration is the earliest and clearest signal that a motor is developing a problem. Long before a motor gets hot, noisy or trips out, its vibration level starts to climb — from imbalance, misalignment, looseness or bearing wear. Catching that rise early means you can plan a repair instead of suffering an unplanned breakdown. Because a phone is always in your pocket, it is the ideal tool for the frequent quick checks that catch problems early, using the accelerometer meter.

Where to measure on a motor

Take readings at the motor’s bearing housings — the solid metal directly over each bearing — at both the drive end (the coupling/pulley side) and the non-drive end (the fan/rear side). At each bearing, measure in three directions:

• Horizontal — usually the highest reading; most sensitive to imbalance.
• Vertical — sensitive to looseness and weak mounting.
• Axial (along the shaft) — the key direction for misalignment and bent shafts.

Avoid measuring on the terminal box, cooling shroud or any sheet-metal cover — those resonate and exaggerate the reading. Press the phone firmly and flat against bare housing metal and let the value settle on the vibration meter.

What your reading means: common motor faults

The overall mm/s value tells you how bad; the frequency spectrum tells you what. Here are the signatures of the most common motor faults:

Fault	Spectrum signature	Tell-tale sign
Imbalance	Dominant peak at 1× running speed	High horizontal vibration
Misalignment	Strong 2× peak	High axial vibration
Mechanical looseness	Many harmonics (1×, 2×, 3×…)	Erratic, directional readings
Bearing wear	High-frequency peaks	Often above a phone’s range
Electrical fault	Peak at 2× line frequency (100/120 Hz)	Vibration vanishes instantly at power-off

To use it: find the dominant peak in the spectrum, divide its frequency by your motor’s 1× frequency (RPM ÷ 60), and read the multiple. A peak at exactly 1× is imbalance; at 2×, misalignment. The sensor app highlights the dominant frequency for you, so you can go from a high reading to a likely cause in one session.

What’s a good motor vibration reading?

As a quick benchmark for a typical medium motor on a rigid base: under 2.8 mm/s RMS is good, 2.8–4.5 mm/s warrants investigation, and above 4.5 mm/s needs action. Smaller motors should read lower. The most reliable judgement, though, comes from comparing against the motor’s own baseline — record a reading when it is healthy and watch for any climb using the logged history in the app.

✓ Pro tip: To confirm an electrical fault, watch the reading the instant you cut power. Mechanical vibration coasts down with the motor; electrically induced vibration disappears the moment the supply is removed. It is one diagnostic a phone can help with even at low frequencies.

What a phone can and can’t catch on a motor

A phone reliably measures the overall RMS velocity for trending on any motor, and it captures the low-frequency mechanical faults — imbalance and misalignment — on motors up to roughly 3,000 RPM, where the fundamental sits within the sensor’s range. What it generally cannot resolve are the high-frequency signatures of early bearing wear and the 100/120 Hz electrical peaks, which sit above a phone’s usable band. For those, a dedicated analyser is the right tool — but for everyday screening and trending, the Vibration Detector Sensor app covers the faults you are most likely to meet.

Trend every motor in your plant — free

Live RMS & peak in mm/s, a dominant-frequency spectrum, session logging and CSV export. Baseline your motors today and catch the climb before it becomes a breakdown.

► Get Vibration Detector Sensor on the App Store  |  Explore the app →

Note: A smartphone accelerometer is well suited to screening and trending of motor vibration, but it is not a substitute for a certified, calibrated analyser for high-frequency bearing diagnostics or compliance-grade measurement.

Frequently Asked Questions

How do I measure motor vibration with my phone?

Open a vibration meter app, press your phone firmly and flat against the motor’s bearing housing while the motor runs under normal load, and read the live RMS velocity in mm/s. Take a reading at both bearings in the horizontal, vertical and axial directions, and save the highest value as your baseline.

What is a normal vibration level for an electric motor?

For a typical medium motor on a rigid base, under 2.8 mm/s RMS is good, 2.8–4.5 mm/s warrants investigation, and above 4.5 mm/s needs action. Smaller motors should read lower, and the most reliable benchmark is the motor’s own healthy baseline.

Where do you measure vibration on a motor?

Measure on the bearing housings at both the drive end and non-drive end — the solid metal directly over each bearing. At each point take readings horizontal, vertical and axial. Avoid the terminal box, cooling shroud and any sheet-metal cover, which distort the reading.

What does high motor vibration mean?

It means a developing mechanical or electrical problem. A dominant peak at running speed points to imbalance, a peak at twice running speed points to misalignment, multiple harmonics suggest looseness, and a peak at twice line frequency suggests an electrical fault. The frequency spectrum identifies which.

Can a phone detect motor bearing problems?

A phone can catch advanced bearing problems that raise the overall vibration level, but early bearing defects show up at high frequencies above a phone’s usable range, so they are best detected with a dedicated analyser. For routine screening and trending, a phone is still valuable.

What causes an electric motor to vibrate?

The most common causes are imbalance (dirt or wear on the rotor), shaft misalignment with the driven machine, mechanical looseness, worn bearings, a soft foot or weak mounting, and electrical faults in the windings or rotor. Each leaves a distinct signature in the vibration spectrum.

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