Vibration Severity Zone (ISO 20816)

Because the same absolute velocity means different things on a 10 hp pump and a 2,000 hp compressor on a soft foundation. ISO 20816 splits machines into classes by power and mounting, and within a class the three zone boundaries are fixed velocities -- so the reading and the class together give the answer with no judgment required, which is exactly what makes it useful to a technician who is not a vibration analyst. Zone A is new-machine condition, B is acceptable for unrestricted long-term operation, C is unsatisfactory for the long term and means plan the work rather than necessarily shut down, and D is severe with damage possibly occurring. A 60 hp pump on the Class II boundaries reading 0.135 in/s sits in zone C: above the 0.110 B/C boundary and below the 0.280 C/D. THE ZONE IS A SCREEN, NOT A DIAGNOSIS. A reading in zone C says something is wrong and says nothing whatever about what; the forcing-frequency and bearing-defect calculations are what turn an overall level into a cause. Equally important is the CHANGE, which is the part a single reading cannot show: a machine that has gone from 0.062 to 0.135 in/s in six months has grown 118% and crossed a boundary in one interval, and a machine that has merely doubled from 0.06 to 0.12 is telling a clear story even though both readings sit inside zone B. The standard's own guidance treats a significant change as actionable regardless of zone, and that rate is what turns a scheduled inspection into a planned outage before it becomes an unplanned one. NO CLASS TABLE IS SHIPPED: the boundaries are entered, because they depend on the class, on the edition, and on whether the plant has adopted its own limits. This is an overall broadband velocity screen. It does not diagnose, identify a fault, or evaluate displacement or acceleration, and an overall velocity in the standard's band is insensitive to exactly the high-frequency energy that early bearing damage produces -- a bearing can be failing with the overall reading firmly in zone B. It does not address measurement quality: transducer mounting, location, direction, and the band the instrument actually integrated all change the number, and readings taken differently are not comparable, which matters most for the trend. ISO 20816, the machine manufacturer's limits, and the plant's condition monitoring programme govern.

the overall broadband velocity reading is placed in zone A, B, C or D against the three boundary velocities entered for the machine class; 1 mm/s = 0.03937 in/s; the trend is the percent change from a previous reading and its rate per month.

The ISO 20816 vibration severity zones A/B/C/D, CITED NOT MIRRORED: the class boundaries are entered because they depend on the machine class, the edition, and the plant's adopted limits. Zone A is new-machine condition, B acceptable for unrestricted long-term operation, C unsatisfactory long-term, D severe. ISO 20816, the machine manufacturer's limits, and the plant's condition monitoring programme govern.

A comparison against boundaries the user enters; no class table from the standard is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: reading, reading_is_mm_s, boundary_ab, boundary_bc, boundary_cd, previous_reading, interval_months, reading_in_s, reading_mm_s, margin_to_next_zone_in_s, change_pct, change_per_month_in_s

• No class boundary table is shipped boundaries are entered from the adopted edition and classISO 20816
• A screen, not a diagnosis the forcing and defect frequencies turn a level into a causecondition monitoring practice
• Readings taken differently are not comparable transducer mounting, location and band all change the numbercondition monitoring practice