The Complete Handbook of Vibration Meters

Chapter 1: Understanding Vibration Meters

What a Vibration Meter Actually Measures

A vibration meter is a single-purpose instrument that converts mechanical motion into an electrical signal, then processes that signal into a number you can read. That number is typically expressed as acceleration (in meters per second squared, or g), velocity (in millimeters per second or inches per second), or displacement (in micrometers or mils). The physical reality it measures is the same in all three cases: a machine part moving back and forth around its resting position. But the way that motion is represented matters enormously for what the reading tells you.

The most common mistake made by inexperienced users is treating the meter like a thermometer - place it on the machine, read the number, and compare it to a fixed threshold. This is only valid if you are measuring the same machine, at the same point, under the same load conditions, with the same sensor mounting, using the same measurement unit, and ideally at the same running speed. Change any one of those variables and the number changes, often by a factor of two or more. A vibration reading is only meaningful as part of a comparison - either against a baseline reading you took earlier, against a published severity chart for your machine class, or against a sister machine in identical service.

Consider a concrete example: a 30 kW electric motor driving a centrifugal pump at 2950 RPM. If you mount an accelerometer on the bearing