Glossary

Sounds of a frequency higher than 20,000 Hz. The frequency region containing these frequencies is called the ultrasonic region.

The combustible portion of the fuel which is not completely oxidized.

Independent United States testing organization that sets safety standards for motors and other electrical equipment.

The highest concentration (expressed in percent vapour or gas in the air by volume) of a substance that will burn or explode when an ignition source is present.

The ratio of hours in operation to the total hours in that period.