ISO 18436-2 vibration analyst categories: CAT II vs CAT III

What ISO 18436-2 is

ISO 18436 is the international series on qualifying and assessing people who work in condition monitoring and diagnostics of machines. Part 2 covers vibration condition monitoring and diagnostics. It defines four categories of vibration analyst, from Category I, who collects data, to Category IV, who handles the hardest diagnostic and rotor dynamics problems.

The standard sets what each category must know and do. Certification itself comes from certification bodies that follow ISO 18436-1 and the training requirements in ISO 18436-3, so the certificate names the body, for example the Vibration Institute or the Mobius Institute Board of Certification, together with the ISO 18436-2 category.

The four categories at a glance

CAT II vs CAT III: the practical difference

Both categories analyze vibration. The difference is depth and responsibility.

• A CAT II analyst answers "what is wrong with this machine". They read the spectrum and waveform, recognize the common fault patterns, judge severity and write the recommendation. Most findings on pumps, fans, motors and gearboxes in a route-based or online program are CAT II work.
• A CAT III analyst answers "is the program finding the right things, and what is going on when the usual patterns don't fit". They decide what to measure and how often, set and review alarm limits, confirm difficult diagnoses with phase, cross-channel and envelope measurements, investigate resonance and structural problems, and check the CAT II work.

A simple rule: a program needs CAT II analysts to keep up with the findings and at least one CAT III analyst to own the program and the hard cases.

What it takes to be certified

Each category builds on the one below. A candidate needs recognized training, documented field experience and a passed exam. The figures below are the usual ones, cumulative from Category I; the exact numbers depend on the edition of the standard and the certification body.

Certification bodies set their own pass mark and rules for experience and recertification, typically every five years. Check the current requirements with the body you plan to certify through.

What the Category II exam covers

The Category II body of knowledge is the everyday toolkit of a vibration analyst:

• signal processing: sampling, resolution, windows, averaging and the FFT;
• transducers and mounting, and how they limit the usable frequency range;
• spectrum and time waveform analysis, units and scaling;
• fault diagnosis: unbalance, misalignment, looseness, rolling element bearings, gears, electrical faults, pumps and fans;
• severity assessment and standards such as ISO 20816;
• corrective action: alignment and single-plane balancing.

Category III adds program management, phase and cross-channel analysis, envelope and demodulation techniques, resonance testing and a deeper look at bearings, gears and motor faults, including motor current analysis.

Why the category matters when you buy monitoring

Automated diagnosis has changed how much of the routine work a human has to do, but it hasn't removed the need for a qualified person to stand behind a recommendation that stops a machine. When a vendor or service provider says findings are reviewed by analysts, ask which category, and which certification body issued it. A CAT II review is enough for most routine findings; problems that don't fit the usual patterns call for CAT III.

How Misoki uses this

Prism AI reads every measurement and names the fault behind a change: bearing defects, unbalance, misalignment and looseness, gear and motor faults. Findings that matter are then reviewed by ISO CAT II/III vibration analysts before they reach you, together with the evidence behind them.

Frequently asked questions