Avionics online test on “Gyroscopes – 2”.
1. Which of the following systems do not use MEMS gyro?
a) Space launch vehicles
b) Flight control systems
c) Missile guidance
d) Car stability systems
Answer: a
Clarification: MEMS gyros are being exploited not only in avionic applications such as flight control, standby attitude and heading reference systems, and missile mid-course guidance but also in the automobile industry in car stability enhancement systems. Space launch vehicles use ring laser gyros which are more accurate.
2. Why is a tuning fork gyro better than the vibrating cylinder type gyro?
a) Reduce base motion
b) Low power consumption
c) Easy to manufacture
d) Low run up time
Answer: a
Clarification: The vibrating mass rate gyro is a simple instrument suffers from the unacceptable characteristic that the smallest linear motions applied to its base cause unacceptably large errors. To overcome the effect of base motion, it is necessary to use balanced oscillations in which the oscillations of one mass are counter-balanced by equal and opposite motion of a second equal mass as in the case of tuning fork gyro.
3. Which type of gyros works by calculating the difference in time taken by light to travel in a closed circle?
a) Ring laser gyro
b) MEMS gyro
c) Floated gyro
d) Dry tuned gyro
Answer: a
Clarification: Optical gyroscopes such as the ring laser gyro and the fibre optic gyro measure angular rate of rotation by sensing the resulting difference in the transit times for laser light waves travelling around a closed path in opposite directions.
4. What is the basic principle by which laser gyros work?
a) Coriolis effect
b) Conservation of momentum
c) Sagnac effect
d) Mass conservation
Answer: c
Clarification: The Sagnac effect is a relativistic phenomena of light in a rotating reference system. When laser beams circulate in a closed path that is rotating in an inertial space, the optical length seen by the co-rotating beam appears longer than that seen by counter rotating beam.
5. Which of the following type of gyro works by counting the nodes of standing waves of laser beams?
a) Ring laser gyro
b) Optical fiber gyro
c) Dry tuned gyro
d) Floated gyro
Answer: a
Clarification: In a Ring laser gyro, the counterpropagating beams form resonant nodes within the gyro cavity and create an electromagnetic standing wave that remains fixed with inertial space. When the housing of the gyro rotates, a detector can count nodes of the standing waves, each of which represents an angle.
6. A fiber optic gyro measures rotation using the _______ of the two beams?
a) Intensity difference
b) Resonance
c) Interference intensity
d) Wavelength difference
Answer: c
Clarification: In a fiber optic gyro, The counterpropagating beams are launched into an optical path and are recombined as they exit. The interference generated by the recombination depends on the optical phase difference between the two beams and therefore provides a measure of rotation.
7. In two mode RLGs, only linearly polarized modes can be resonant in the cavity.
a) True
b) False
Answer: a
Clarification: Two mode RLGs are planar by design so that only linearly polarized modes can be resonant in the cavity. Suppression of one of the two modes of polarization ensures stable operation.
8. The emission of photons by the gas medium that fills the RLG cavity is called as?
a) Laser discharge
b) Spontaneous discharge
c) Spontaneous emission
d) Laser emission
Answer: c
Clarification: The gas medium that supplies the gain for the laser also occasionally emits photons which are unrelated to the laser signal. This is known as spontaneous emissions are leads to noise and random walk in the RLG angle output.
9. What is the cause of lock-in phenomena in RLG?
a) Backscatter
b) Low intensity
c) High intensity
d) Low standing wave ratio
Answer: a
Clarification: Lock-in phenomenon leads makes the RLG insensitive to low angular rates. The cause of the lock-in phenomenon is backscatter within the cavity, usually resulting from imperfections in or particulates in the mirror surfaces.
10. Which method uses a turntable in RLG to reduce lock-in errors?
a) Intensity control
b) Rate biasing
c) Using mechanical dither
d) Random rate fixing
Answer: b
Clarification: The method of rate biasing employs a turntable that applies a constant rotation to the gyro. An angular encoder measures the relative angle between the instrument and its base.
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