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An inertial reference unit (IRU) is a type of 
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.
Optical Inertial Reference Units (IRUs)
Navigational equipment Aircraft instruments Avionics {{technology-stub
inertial sensor
An inertial measurement unit (IMU) is an electronic device that measures and reports a body's specific force, angular rate, and sometimes the orientation of the body, using a combination of accelerometers, gyroscopes, and sometimes magnetomete ...
which uses gyroscopes (electromechanical, ring laser gyro
A ring laser gyroscope (RLG) consists of a ring laser having two independent counter-propagating resonant modes over the same path; the difference in phase is used to detect rotation. It operates on the principle of the Sagnac effect which shif ...
or MEMS
Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
) and accelerometers
An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acce ...
(electromechanical or MEMS
Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
) to determine a moving aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engine ...
’s or spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
’s change in rotational attitude (angular orientation relative to some reference frame) and translational position (typically latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
, longitude
Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lette ...
and altitude
Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...
) over a period of time. In other words, an IRU allows a device, whether airborne or submarine, to travel from one point to another without reference to external information.
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.
See also
*Air data inertial reference unit An Air Data Inertial Reference Unit (ADIRU) is a key component of the integrated Air Data Inertial Reference System (ADIRS), which supplies air data (airspeed, angle of attack and altitude) and inertial reference (position and attitude) information ...
* Inertial measurement unit
External links
Optical Inertial Reference Units (IRUs)
Navigational equipment Aircraft instruments Avionics {{technology-stub