The HRG is often referred to as the Wineglass gyro as the CVG properties for a wineglass were first discovered and noted by Bryan in 1891. Due to Coriolis Forces, a vibration standing wave pattern induced on a hemispherical, cylindrical, or similarly shaped resonating cavity, rotates relative to the gyro case by a fraction of the rotation angle experienced about the angle of symmetry. The wave rotation scale factor is a function of resonator geometry but for a hemisphere is ≈ 0.3.
High quality Hemispherical Resonators are commonly machined from quartz, due to its excellent mechanical properties and it is the dimensional accuracy of the precision ground and polished unit which determines its accuracy. Temperature effects remain critical in this respect producing quadrature non-uniform mass distribution.
The system is robust, with almost no moving parts and can be very accurate, under strictly controlled temperature environments. Litton, now part of Northrop Grumman, produces a unit with < 0.01°/hr performance which is used by the military and for space flight in which it has recorded millions of operating hours without failure. This system has potential for oilfield use but is expensive, requires significant temperature stabilization which results in size implications. The system is also covered by the international arms trafficking laws with all the implications and restrictions applicable as noted above for RLG.
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