An inertial reference unit (IRU) is a type of inertial sensor which uses gyroscopes (electromechanical, ring laser gyro or MEMS) and accelerometers (electromechanical or MEMS) to determine a moving aircraft’s or spacecraft’s change in rotational attitude (angular orientation relative to some reference frame) and translational position (typically latitude, longitude and altitude) over a period of time. Another name often used interchangeably with IRU is Inertial Measurement Unit.
The two basic classes of IRUs/IMUs are "gimballed" and "strapdown". The older, larger gimballed systems have become less prevalent over the years as the performance of newer, smaller strapdown systems has improved greatly via the use of solid-state sensors and advanced real-time computer algorithms. Gimballed systems are still used in some high-precision applications where strapdown performance may not be as good.
Famous quotes containing the words reference and/or unit:
“In sum, all actions and habits are to be esteemed good or evil by their causes and usefulness in reference to the commonwealth, and not by their mediocrity, nor by their being commended. For several men praise several customs, and, contrarily, what one calls vice, another calls virtue, as their present affections lead them.”
—Thomas Hobbes (1579–1688)
“During the Suffragette revolt of 1913 I ... [urged] that what was needed was not the vote, but a constitutional amendment enacting that all representative bodies shall consist of women and men in equal numbers, whether elected or nominated or coopted or registered or picked up in the street like a coroner’s jury. In the case of elected bodies the only way of effecting this is by the Coupled Vote. The representative unit must not be a man or a woman but a man and a woman.”
—George Bernard Shaw (1856–1950)