ISO 13373 is a multi-part standard for condition monitoring and diagnostics of machines using vibration. It covers general procedures, data processing, guidelines for vibration diagnosis, and recommendations for monitoring parameters and thresholds.

What is the difference between alarm and danger thresholds?

Alarm threshold indicates abnormal condition requiring investigation and planned maintenance. Danger threshold indicates imminent failure risk requiring immediate action — shutdown or load reduction. Danger is typically 2× the alarm value.

How do I set vibration alarm levels?

Alarm levels can be set based on: (1) absolute ISO standards, (2) baseline × multiplier (e.g., 2.5× baseline for alarm, 4× for danger), or (3) statistical methods using historical data (mean + 2σ for alarm, mean + 3σ for danger).

Which vibration parameter should I monitor?

Velocity (mm/s RMS, 10–1000 Hz) is the most common for general machinery per ISO 10816. Displacement (μm p-p) for shaft relative vibration per ISO 7919. Acceleration (g) for high-frequency defects like bearing faults and gear mesh.

What is the relationship between ISO 13373 and ISO 10816?

ISO 13373 provides general guidelines for condition monitoring methodology, while ISO 10816 (now ISO 20816) provides specific numerical vibration severity limits for different machine categories. They are complementary standards.

Free Engineering Tool — #028

Condition Monitoring — ISO 13373

Reference tool for ISO 13373 condition monitoring parameters. Select machine type and enter measured vibration to determine status against alarm and danger thresholds.

ISO 13373ISO 10816 / 20816Alarm / Danger

Machine Type

Vibration Parameter

Measured Value (mm/s RMS)

Baseline Value (optional)

Quick presets

Assessment

Machine Status

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Zone A/B Boundary (Good)

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Zone B/C Boundary (Alarm)

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Zone C/D Boundary (Danger)

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Change from Baseline

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ISO 10816 Vibration Severity Zones

Vibration severity is classified into four zones:

Zone A — New or reconditioned machines
Zone B — Acceptable for unrestricted long-term operation
Zone C — Alarm — acceptable only for limited periods
Zone D — Danger — may cause damage

Velocity Thresholds (mm/s RMS)

Zone Boundary	Group 1	Group 2	Group 3	Group 4
A/B	2.3	3.5	1.4	0.7
B/C (Alarm)	4.5	7.1	2.8	1.8
C/D (Danger)	7.1	11.2	4.5	4.5

Baseline Monitoring

A change ratio > 2.5× baseline suggests developing fault. > 4× requires immediate investigation.

ℹ️ Note: These are general guidelines from ISO 10816-3. Specific machine types may have different criteria per specialized parts of ISO 20816.

Condition Monitoring Parameters — ISO 13373 | Alarm & Danger Thresholds | Free Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Assessment

ISO 10816 Vibration Severity Zones

Velocity Thresholds (mm/s RMS)

Baseline Monitoring