Question

Describe the principles and operations of movement sensors: Doppler-Effect Velocity sensor and Spring-Mass Accelerometor; State the advantage and disadvantage of each type of movement sensors.

Answer 1

Doppler effect velocity sensor:

• It is a specialized doppler radar which uses the doppler effect to measure the three orthogonal velocity components referenced to the aircraft.

Principles and operations:

• so ,by using this sensor we measure an aircraft three dimensional velocity .A doppler radar antenna is caused to radiate a minimum of three non-coplanar microwave beams towards the earth surface.some energies get back to the radar by the earth surface.By combining beam angles and three or more doppler frequencies we get the components of aircraft velocity.

Advantages and disadvantages:

1. these are used on helicopters for navigation,sonar dropping,target handover for weapon delivery and for search and rescue.
2. it also measures the velocity relative to the surface,sea current and tidal effects.
3. as the air craft moves back scattering coefficient changes within the beam width and causes some error in the  velocity .so, a major error is that they suffer typically from accumulated error .

Spring-Mass Accelerometer:

it is a sensor that it measures physical acceleration experienced by an object due to inertial forces or due to mechanical excitation ,so it behave as a damped mass on a spring

Principles and operations:

• It contains a piezoelectric crystal element bonded to a mass.when it is subjected to a force,the mass compresses the crystal ,causing it to produce an electrical signal that is proportional to the level of force applied.

Advantages and disadvantages:

• it is used in android platform as sensors which let us monitor the motion of the device in which they are hardware and software based sensors.
• the sensor itself cant provide the velocity.