When you measure vibration on a pump or motor, the reading needs a yardstick before it means anything: is 4 mm/s fine or a warning? The ISO 10816 standard, and its successor ISO 20816, provide that yardstick by grading overall vibration into evaluation zones that tell you whether a machine is fit to run, needs watching, or should be shut down. The measure it uses is the overall RMS velocity in millimeters per second, evaluated against boundaries that depend on the type and mounting of the machine. It is the foundation on which most vibration alarm and trip thresholds are built.
ISO 10816 vibration severity in one line: ISO 10816, now largely superseded by ISO 20816, is the standard that classifies machine condition by the overall RMS vibration velocity measured on non-rotating parts such as bearing housings. It sorts the reading into evaluation zones A through D, where A is a new-machine condition and D is likely to cause damage, with the zone boundaries set according to the machine's class and mounting.
The standard is built on a single broadband number: the overall RMS velocity, typically measured on the bearing housing or another non-rotating part of the machine over a defined frequency band. Velocity in millimeters per second is used because, across the mid-frequency range where most rotating-machine faults live, velocity correlates well with the fatigue-inducing severity of the vibration. Rather than looking at individual frequencies, this overall value rolls the whole vibration signature into one figure that represents the machine's general condition.
That number is then placed into one of four evaluation zones. Zone A is the range typical of newly commissioned machines. Zone B is considered acceptable for long-term unrestricted operation. Zone C indicates a machine that is not suitable for continuous long-term running and should be regarded as usable only for a limited period until a repair opportunity arises. Zone D represents vibration severe enough to be capable of causing damage. The zones give operators a plain-language verdict, run freely, keep running but plan a repair, or stop, without needing to interpret a raw number in isolation.
It is worth being clear about what the standard does and does not do. It grades overall severity to judge whether a machine is fit to run; it does not diagnose the cause. A machine sitting in zone C tells you it is vibrating too much for comfort, but not whether the cause is imbalance, misalignment, or a bearing fault. That diagnostic step needs spectral analysis. The zones answer the acceptance question, and a separate spectrum answers the what-is-wrong question.
A number that is alarming on one machine is perfectly normal on another, so the standard does not use a single set of boundaries. The same overall velocity means different things on a small pump than on a large turbine-generator, so machines are grouped by characteristics such as size, power, and type, and each group gets its own zone boundaries. A large, robust machine tolerates higher velocity before it reaches zone C than a small one does, and the standard's tables reflect that by shifting the boundaries per group.
Mounting matters just as much. The standard distinguishes between rigidly mounted machines and those on flexible supports, because a flexible foundation changes how vibration at the bearing relates to the forces inside the machine and to the stress the structure sees. The same RMS velocity is evaluated against different limits depending on whether the machine and its base behave as a rigid or a flexible system. Getting the classification right, machine group and support condition, is what makes the zone verdict meaningful; applying a turbine's limits to a small pump, or rigid-mount limits to a flexibly mounted set, produces misleading alarms.
ISO 20816 is the current evolution of this family and consolidates and updates the earlier ISO 10816 parts, keeping the same overall-velocity-into-zones philosophy while refining the measurement guidance and machine categories. In practice many operators still refer to the numbers as ISO 10816 limits, and for setting broadband alarm thresholds the two are aligned in intent. The key point that carries across both is that a severity verdict is only valid once the machine has been correctly categorized.
The zone boundaries translate directly into alarm and trip thresholds, which is where the standard becomes operational. The B-to-C boundary makes a natural warning level: crossing it means the machine has moved out of acceptable long-term operation and someone should plan a repair. The C-to-D boundary makes a natural danger or trip level: crossing it means the vibration is now capable of doing damage and continued running is a risk. Because the boundaries are defined per machine class, a monitoring system can pre-populate sensible thresholds instead of relying on an operator to guess them.
A SCADA historian is the natural home for this because it continuously logs the overall velocity and compares it to those thresholds. Merobix trends the broadband RMS value from each measurement point against the class-appropriate zone boundaries, so a machine that drifts from zone B into zone C raises a warning automatically and a machine reaching zone D raises a danger alarm, without an operator having to watch every reading. For fleets of pumps, motors, and fans spread across remote sites, that automatic comparison to a recognized severity standard is what makes broad vibration coverage practical.
Trending the overall value over time adds what a single reading cannot: rate of change. A machine can sit safely in zone B for years, but a value climbing steadily toward the B-to-C boundary is a developing problem worth investigating before it alarms. Historized data lets operators establish each machine's normal baseline within its zone and watch for the upward trend, turning the standard from a pass/fail gate into an early-warning tool. When a zone alarm does fire, the same history shows how fast the machine got there, which helps decide whether to intervene now or on the next planned outage.
Zone A is the vibration level typical of a newly commissioned machine. Zone B is acceptable for long-term unrestricted operation. Zone C is not suitable for continuous long-term running and means the machine should be repaired at the next opportunity. Zone D is severe enough that the vibration can cause damage, so the machine should be stopped.
ISO 20816 is the current standard that consolidates and updates the earlier ISO 10816 series, while keeping the same approach of grading overall RMS velocity into evaluation zones. The measurement philosophy and the meaning of the zones carry across both. Many operators still call the limits ISO 10816 values, and for setting broadband vibration alarms the two are aligned in intent.
No. The standard grades overall vibration severity to judge whether a machine is fit to keep running, but it does not diagnose the cause. A machine in zone C is vibrating too much, but whether the cause is imbalance, misalignment, or a bearing fault requires spectral analysis of the vibration. The zones answer the acceptance question, and a frequency spectrum answers what is actually wrong.
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