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A rate gyro refers to a gyro that puts out some sort of signal that is proportional to its rotational velocity. Originally gyro’s where large mechanical devices. Nowadays, purely mechanical gyro’s have been replaced by small, lightweight solid-state ones. There are now three main types of solid-state gyro’s: piezoelectric, fiber-optic gyro’s (FOG’s), and ring laser gyro’s (LRG’s). Most of the time, when someone refers to a solid-state gyro they mean a piezoelectric one as they are by far the least expensive and most common piezoelectric gyro is a small silicon or quartz "tuning fork" that deforms due to the coriolis force when it is rotated. Tokin’s use a piezoelectric ceramic instead of silicon or quartz. The deformation is measured by a sensor that amplifies the signal. There is a nice animation of this at http://www.systron.com/theory.html. Even though they are commonly advertised as "non-mechanical" and "no moving parts", they are in fact electromechanical. Solid-state rate gyro's are also considered MEMS (Micro Electro Mechanical Systems). Because piezoelectric gyro’s measure rotation via a vibrating tuning fork, they are susceptible to picking up noise due to external vibration and resonant coupling of the tuning forks. Two-axis piezoelectric units need tuning forks that operate at slightly different frequencies to try and avoid this unwanted coupling. Another (more expensive) type of solid-state rate gyro is a fiber-optic gyro (FOG). These use the phase difference of laser light in two beams traveling in opposing rings to measure rotation using the Sagnac effect. An explanation can be found at http://www.kvh.com/pdf/ECoreTech.pdf. FOG’s can still pickup noise due to vibration but not due to resonant coupling because they don't use tuning forks. Ring laser gyro’s (LRG’s) also exploit the Sagnac effect. All I know is that FOG’s sell for $1000’s and LRG’s sell for $10,000’s. FOG’s and LRG’s are also known as optical gyro’s.
Here’s a quick summary. The details are in the second table below.