# Vibration Fault Signature Diagnosis Reference Table

> Source: https://netray.co/tools/vibration-fault-signature-diagnosis-reference
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

A searchable lookup of what each common machine fault looks like in a vibration spectrum, with dominant frequency, direction and the first check to make.

## Category

maintenance

## Industry

Discrete Manufacturing

## Audience

- Reliability engineer
- Vibration analyst
- Maintenance planner

## Tool

**Kind:** worksheet

**Mode:** reference

**Columns:**

#### Fault

**Key:** fault

**Type:** text

#### Dominant frequency

**Key:** freq

**Type:** text

#### Strongest direction

**Key:** dir

**Type:** text

#### Spectrum features

**Key:** features

**Type:** text

#### First check

**Key:** check

**Type:** text

**Rows:**

**Fault:** Unbalance (static)

**Freq:** 1x running speed

**Dir:** Radial

**Features:** Single clean 1x peak, phase steady and in phase across the bearings

**Check:** Look for buildup, missing weights, damaged fan blades

**Fault:** Unbalance (couple)

**Freq:** 1x running speed

**Dir:** Radial

**Features:** 1x peak with phase about 180 degrees out between the two bearings

**Check:** Two plane balance, check rotor geometry

**Fault:** Overhung rotor unbalance

**Freq:** 1x running speed

**Dir:** Radial and axial

**Features:** High 1x in both directions, axial phase steady

**Check:** Inspect fan or impeller, check for bent shaft

**Fault:** Bent shaft

**Freq:** 1x, sometimes 2x

**Dir:** Axial

**Features:** High axial 1x with axial phase about 180 degrees across the machine

**Check:** Dial indicator runout on the shaft

**Fault:** Angular misalignment

**Freq:** 1x with 2x and 3x

**Dir:** Axial

**Features:** High axial 1x and 2x, axial phase about 180 degrees across the coupling

**Check:** Laser alignment, check coupling gap and soft foot

**Fault:** Parallel (offset) misalignment

**Freq:** 2x running speed, often 1x also

**Dir:** Radial

**Features:** 2x peak often above 1x, radial phase about 180 degrees across the coupling

**Check:** Laser alignment, check thermal growth

**Fault:** Soft foot

**Freq:** 1x, sometimes 2x

**Dir:** Radial

**Features:** Elevated 1x that changes when a hold-down bolt is loosened

**Check:** Loosen each foot in turn and watch the reading

**Fault:** Structural looseness (base, frame)

**Freq:** 1x

**Dir:** Vertical

**Features:** Large vertical 1x, big phase difference between machine foot and base

**Check:** Check hold-down bolts, grout, frame cracks

**Fault:** Bearing housing looseness

**Freq:** Harmonics of 1x, up to 10x

**Dir:** Radial

**Features:** Many running speed harmonics, sometimes 0.5x subharmonics, noisy floor

**Check:** Check housing fit, cap bolts, bearing outer race fit

**Fault:** Rotating looseness (rub, loose fit)

**Freq:** 0.5x, 1.5x, 2.5x subharmonics

**Dir:** Radial

**Features:** Fractional harmonics at half-order multiples

**Check:** Check shaft to bearing fit, impeller or sleeve fit

**Fault:** Rolling element bearing wear

**Freq:** Bearing defect frequencies (BPFO, BPFI, BSF, FTF), non-synchronous

**Dir:** Radial and axial

**Features:** Non-integer multiples of 1x, sidebands at 1x for inner race, rising noise floor in late stages

**Check:** Compare against the bearing frequency table, check envelope spectrum

**Fault:** Early bearing defect

**Freq:** High frequency, kHz range

**Dir:** Radial

**Features:** Rise in high frequency band, enveloping or spike energy before running speed spectrum changes

**Check:** Envelope analysis, ultrasound, trend high band

**Fault:** Journal bearing oil whirl

**Freq:** 0.40x to 0.48x running speed

**Dir:** Radial

**Features:** Peak just under half of running speed, can lock up to rotor critical speed

**Check:** Check oil viscosity and temperature, clearance, loading

**Fault:** Gear tooth wear

**Freq:** Gear mesh frequency (teeth x shaft speed) with sidebands

**Dir:** Radial and axial

**Features:** Gear mesh peak with sidebands at the speed of the worn gear

**Check:** Compare to baseline, inspect tooth contact pattern

**Fault:** Cracked or broken gear tooth

**Freq:** 1x of the damaged gear with sidebands around mesh

**Dir:** Radial

**Features:** Strong sidebands at running speed of the damaged gear, time waveform shows impact once per revolution

**Check:** Inspect gear, review the time waveform

**Fault:** Gear eccentricity or backlash

**Freq:** Gear mesh with sidebands, 2x mesh

**Dir:** Radial

**Features:** Elevated mesh amplitude that varies with load, sidebands at gear speed

**Check:** Check backlash, shaft runout, gear mounting

**Fault:** Blade or vane pass problem

**Freq:** Number of blades x running speed

**Dir:** Radial

**Features:** Peak at blade pass frequency, higher when clearance to the casing is uneven

**Check:** Check impeller to volute clearance, flow conditions

**Fault:** Pump cavitation

**Freq:** Broadband random, high frequency

**Dir:** Radial

**Features:** Raised noise floor at high frequency, often with blade pass peak, sounds like gravel

**Check:** Check suction pressure, NPSH margin, strainer

**Fault:** Belt wear or mistension

**Freq:** 1x to 4x belt frequency

**Dir:** Radial

**Features:** Peaks at belt frequency and harmonics, often with 2x belt as the strongest

**Check:** Check belt condition, tension and sheave wear

**Fault:** Sheave misalignment or eccentric sheave

**Freq:** 1x of the affected sheave

**Dir:** Radial and axial

**Features:** High 1x of the sheave, axial component with misalignment

**Check:** Straightedge or laser check on sheave faces

**Fault:** Electrical: eccentric air gap or stator problem

**Freq:** 2x line frequency

**Dir:** Radial

**Features:** 2x line frequency peak (100 or 120 Hz), disappears on power off

**Check:** Check air gap, stator looseness, supply balance

**Fault:** Electrical: broken rotor bar

**Freq:** 1x with sidebands at pole pass frequency

**Dir:** Radial

**Features:** Sidebands around 1x spaced at the pole pass frequency, best seen under load

**Check:** Motor current signature analysis at full load

**Fault:** Resonance

**Freq:** Natural frequency of the structure

**Dir:** Any

**Features:** High amplitude at one frequency, phase shifts about 180 degrees through the peak during a run up or coast down

**Check:** Bump test, change speed or stiffness

**Fault:** Rotor rub

**Freq:** Many harmonics, sometimes subharmonics

**Dir:** Radial

**Features:** Similar to looseness, may show truncated waveform and a noisy spectrum

**Check:** Check clearances and thermal growth

**Notes:** Signatures are typical patterns, not proof. Confirm with the time waveform, phase and the machine history before replacing parts. Running speed is written as 1x.

## Content

**Intro:** Most vibration calls come down to matching a spectrum to a short list of causes. This reference lists the common faults with the frequency, direction and spectrum features that usually identify them, and a first check to confirm.

**Sections:**

#### How to use the table

**Body:** Start from what you see in the spectrum, not from what you suspect. Find the dominant peak, divide its frequency by running speed to get the order, and search for that order in the table. Then check the direction in which it is strongest and whether the phase supports the diagnosis. Use the search box to filter by fault name or by words such as axial, sidebands or subharmonics. Export the filtered rows to Excel to attach to a condition report or a CMMS work request.

**Bullets:**

- Convert peaks to orders: frequency in Hz divided by running speed in Hz
- Note the direction (radial or axial) of the largest reading
- Compare against the last baseline for the same measurement point
- Check phase when 1x or 2x dominates

#### Why running speed multiples matter

**Body:** Faults that repeat once per revolution show up at 1x and its harmonics. Unbalance, bent shaft, misalignment and looseness all live at integer orders, which is why phase and direction are needed to separate them. Rolling bearing defects and belts are non-synchronous or tied to a different component, so their peaks sit at fractional or unrelated orders. Gears add a mesh frequency equal to teeth times shaft speed, with sidebands that tell you which gear is damaged.

#### Worked example

**Body:** A 1,480 rpm pump motor (24.7 Hz) shows a large peak at 49 Hz in the radial direction, with the axial reading low. The ratio is about 2.0, which points to parallel misalignment or an electrical cause. If the peak is 2x line frequency (100 Hz on a 50 Hz supply) it would be electrical, but here it is 2x running speed, so the next step is a laser alignment check and a look at soft foot. If the peak stays after a realignment, check the time waveform for looseness.

#### Common mistakes

**Body:** Treating any 1x peak as unbalance is the most common error. Always check phase and the axial reading. Another mistake is diagnosing from overall velocity alone, which hides early bearing faults in the high frequency band. Finally, do not skip the baseline: a peak that has always been there is not a new fault.

**Cta:** If your CMMS or ERP already holds asset and work order history, we can help link spectrum alarms to work requests automatically. Ask for an expert review of your condition monitoring data flow.

**Faq:**

#### How do I tell unbalance from misalignment?

**Answer:** Unbalance gives a dominant 1x peak in the radial direction with steady phase. Misalignment gives high 1x and 2x, a strong axial component and phase that is about 180 degrees out across the coupling. Check both radial and axial readings and phase before deciding.

#### What does a peak at half running speed mean?

**Answer:** A peak at about 0.5x and its odd multiples usually points to rotating looseness or a rub. A peak at 0.40x to 0.48x on a journal bearing machine is oil whirl. Confirm with the time waveform and machine type.

#### Do these signatures work for variable speed drives?

**Answer:** Yes, but convert to orders first. At a different speed all synchronous peaks move with the shaft. Electrical peaks tied to line frequency stay fixed on a fixed supply, but with a VFD they follow the drive output frequency.

#### Can this replace a certified vibration analyst?

**Answer:** No. It is a lookup to speed up triage. Severity, remaining life and repair decisions need trended data, phase, waveform review and often a second technique such as oil analysis or thermography.

## Search terms

vibration analysis fault chart, vibration spectrum fault diagnosis, unbalance vs misalignment vibration, vibration fault frequency table, vibration analysis cheat sheet, mechanical looseness vibration signature, gear mesh frequency vibration, vibration troubleshooting guide

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