Ascension's family of tracking
devices are magnetic 6 degree of freedom sensors which can detect their x, y
and z coordinate position and azimuth, elevation and roll orientation
relative to a transmitter.
The transmitter consists of a core about which the X, Y, and
Z antennae are wound. The three orthogonal coils receive DC pulses
from a control unit -- one antenna at a time. While a given
transmitter antenna is being provided with current, readings are taken from
the antennae of the sensor which also consists of three orthogonal coils.
Initially the transmitter is shut off so that the sensor can measure the x,
y, and z components of the Earth's magnetic field. During a measurement
frame, a total of 12 readings are taken. The voltage generated on each
of the sensor's coils will differ depending on the position and orientation
of the sensor in the magnetic field and the antenna that generated the
field. From these data, it is possible to then compute the position and
orientation of the sensor relative to the transmitter.
The range over which a sensor can
operate and the accuracy depend on the type of transmitter and sensors being
used. The measurement rate is also a function of the type of
transmitter and reciever.
Sampling
Rate:
30 to 144Hz for each of two to fourteen sensors.
Range: Extended
Range Transmitter will measure 12 feet from transmitter for total range of
24 feet. Standard range will measure 3 feet from transmitter for total
range of 6 feet.
Position
accuracy:
Extended Range
Transmitter: up to 0.3 inches/0.5 degrees at a five-foot distance from
transmitter and 0.6 inches/1.0 degrees at a ten-foot distance from
transmitter. Standard Range
Transmitter: up to 0.07 inches/0.5 degrees at 36 inch distance from
transmitter. MiniSensors: up to
.07 inches/0.5 degrees at 30 inch distance from transmitter.
Resolution:
Extended Range Transmitter:
is 0.03 inch/0.1 degrees at five feet and 0.1 inch/0.2 degrees at ten feet
from transmitter. Standard Range Transmitter: is 0.03 inch/0.1
degrees at 36 inch distance. Mini
Sensors: is 0.02 inch/0.1 degrees at five feet and 0.1 inch/0.2
degrees at 30 inch distance from transmitter.