Avionics MCQs – Accelerometer
1 - Question
What does the accelerometer measure?
Explanation: The accelerometer is a type of inertial instrument that measures the acceleration in any given axes. The measured acceleration can be integrated over time to obtain velocity and distance.
2 - Question
What is the output given by an accelerometer if the instrument is accelerated upward with an acceleration of 7g?
Explanation: Accelerometer is used to measure acceleration of the vehicle and thus must be corrected for the Earth’s gravitational effect. If the accelerometer is being accelerated upward with an acceleration of 7g, then (a-G) = 7g – (-1g), and the instrument reads 8g.
3 - Question
Which accelerometer uses torquer coil and pick off supported by a flexure to measure acceleration?
a) MEMS accelerometer
b) Flexure pivot accelerometer
c) Vibrating beam accelerometer
d) Mechanical accelerometer
Explanation: The flexure pivot accelerometer is the most commonly used in aircraft systems. The sensitive element consists of a pendulum with a torquer coil and a pick off supported by torsional spring or flexure.
4 - Question
In flexure pivot accelerometer, the torque current is a measure of acceleration.
Explanation: The torquer coil in the accelerometer restore the pendulum to null, the torquer current being a measure of the restoring torque and, hence, of the acceleration.
5 - Question
Why do accelerometers that include fluid damping exhibit reduced damping?
a) State of fluid
d) Thermal characters
Explanation: Accelerometers that include fluid damping exhibit reduced bandwidth and additional thermal sensitivity due to changes in fluid characteristics. Thus flexure pivoted accelerometers are better than floated instruments.
6 - Question
An accelerometer can only measure acceleration in one direction?
Explanation: An accelerometer can only measure acceleration in one axes. In navigational systems comprising of accelerometers, three separate accelerometers are places with each on the three body axes of the aircraft.
7 - Question
Which of the following is true with respect to flexure pivot accelerometers?
a) Flexure must provide maximum resistance in the direction of input axis
b) Flexure must provide maximum resistance in the direction other than input axis
c) Torquer coil current measures the acceleration
d) Unbalanced accelerometer type
Explanation: The pivot or flexure supporting the pendulum must provide minimal restraint for the pendulum in the direction of the input axis while exhibiting high stiffness in the other two directions. The spring constant of the flexure or pivot generates a restoring force that reduces the gain of the electronic restoring loop.
8 - Question
Which of the following conditions cause rectification of vibration inputs?
b) Low voltage
c) High voltage
d) Low current
Explanation: Heating of torquer coil due to rebalance current can lead to rectification of vibration inputs and must often be compensated. A pulse rebalance torquer maintains constant heating.
9 - Question
What does silicon accelerometers use for proof mass sensing and for rebalancing?
c) Metalised wafers
d) Single crystal silicon frame
Explanation: The frame, proof mass and hinges are made with single crystal silicon. Metalised wafers are used to enclose this and also serve as electrodes for sensing proof mass and rebalancing.
10 - Question
Which type of rebalancing technique use voltage applied to pendulum and electrode for correction?
a) Charge forcing
b) Voltage forcing
c) Current forcing
d) Potential forcing
Explanation: In potential forcing, a potential is applied to the pendulum and to one or both the electrodes. The voltage establishes electric fields that induce the charge of the nonconducting pendulum. This causes a net force to act on the proof mass.