VOR station that represents the bearing from the station to
the airborne receiver. The LORAN system operates by the
shipboard receiver determining the time delays of signals
transmitted from two LORAN stations. The GPS operates
by the receiver comparing the time differences and satellite
positions of at least three satellites. LORAN and VOR
systems can be used to determine the position of a vehicle,
while GPS can also determine altitude which is useful for
aircraft and hikers in the mountains.
One of the earliest forms of long distance navigation
was celestial which involves using dead reckoning to
estimate a future position, calculating the position of easily
identifiable stars, and then comparing the actual position
of these stars to determine the actual position. Celestial
navigation uses complex math (hyperbolic trigonometric
functions), data tables of star positions at various times of
the year (Nautical and Air Almanacs), and precision time
pieces. Celestial navigation is a very complex subject which
takes several months of training to master, so I will steer
(very punny) clear of the subject.
All of the forms of navigation rely on a measure of
the speed of the vehicle, the direction of travel, the time
of travel, and a reference such as a map. The accuracy of
your navigation depends on the accuracy of these pieces
Now that we have a very basic understanding of
navigation (there is a lot more to navigation than I am
giving you here), let’s look at the Inertial Navigation System
(INS). The INS measures the vehicle speed, from which
distance traveled is calculated using an accelerometer
and some electronics. Figure 11 show a very basic
accelerometer in which a mass -- which tries to stay in the
same position as the vehicle accelerates -- has a distance
change (displacement) relative to the main body of the
accelerometer. In Figure 11 as the vehicle accelerates
to the right, the mass moves to the left of its rest (not
accelerated) position. The four mass supports provide a
spring action which allows the distance the mass moves to
be relative to the amount of acceleration.
The accelerometer in Figure 11 needs an electronic
means of determining the displacement of the mass such
as a potentiometer, capacitance (mass moves the plate
closer to one plate and farther from the other), a linearly
variable differential transformer (LVDT), or a piezoelectric
material implemented as micro electro-mechanical systems
Figure 12 shows a capacitive MEMS accelerometer
sensor in simplified diagram form. These MEMS
accelerometers are used in electronic items to determine
the orientation of the device in order to present the display
in the proper orientation.
To determine the distance a vehicle has traveled using
the accelerometer signal, we need some electronic circuits
to convert the acceleration output from the accelerometer
sensor to a measure of distance. Acceleration is the rate
n FIGURE 10. Global Positioning System Navigation.
n FIGURE 8. VHF Omni-Range (VOR) Radio Navigation.
n FIGURE 9. LORAN Station Arrangement.
n FIGURE 11. Basic Operation of an Accelerometer.
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