Profilometer

Profilometer is a measuring instrument used to measure a surface's profile, in order to quantify its roughness. Vertical resolution is usually in the nanometre level, though lateral resolution is usually poorer.

Probe Gap

The physical distance between the face of an eddy probe tip and the observed surface. The distance can be expressed in terms of displacement (mils, micrometers) or in terms of voltage (millivolts), which is the value of the (negative) dc output signal and is an electronic representation of the physical gap distance. Standard polarity convention dictates that a decreasing gap results in an increasing (less negative) output signal; increasing gap produces a decreasing (more negative) output signal.

Predictive Maintenance

Usually maintenance that is performed again based on a calendar. The term is usually interchanged with periodic maintenance.

Piezoelectricity

The property exhibited by some materials where a mechanical stress causes the material to produce an electric charge. Both man made and natural piezoelectric materials are used in accelerometers.

Phase Spectrum

Phase frequency diagram obtained as part of the results of a Fourier transform.

Phase Response

The phase difference (in degrees) between the filter input and output signals as frequency varies; usually expressed as lead and lag referenced to the input.

Phase Reference

A signal used in rotating machinery measurements, generated by a sensor observing a once-per-revolution event.

Phase

A measurement of the timing relationship between two signals, or between a specific vibration event and a Keyphasor pulse.

Periodic maintenance

Maintenance that is performed on a calendar or some measure of time basis, i.e., every 12 or 18 months, every so many RPMs, or every so many hours.

Period

The time required for a complete oscillation or for a single cycle of events. The reciprocal of frequency, F=1/T