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RC4600 ACU Board Set
Chapter 2
Hardware
3.2.7 System Performance
The performance achieved by the RC4600 in locating and tracking satellites is dependent on the
mechanical tolerances of the antenna, the correctness of the installation and the accuracy of the various
sensors.
The largest source of error for the system is due to errors in determining the antenna's magnetic heading.
Errors in heading primarily affect the accuracy of the antenna's calculated azimuth position. The
compass determines the magnetic heading by measuring the direction of the magnetic field at the sensor.
Problems arise because the earth's magnetic field can be distorted by ferrous metals (such as steel and
iron; aluminum is a non-ferrous metal) and man-made magnetic fields. These man-made fields can be
generated by electric motors, generators, and transformers.
For the compass sensor, there are two unique categories of objects that distort the magnetic field in the
vicinity of the truck. Some of the distortion is due to objects and electrical devices on the antenna itself.
This component of the distortion can be largely compensated for during system calibration.
The other component of the distortion is due to large metal objects and man-made magnetic fields around
the site where the antenna is being operated. This component of the distortion varies as the antenna
moves from one location to another, and it affects the accuracy of the calculated azimuth position.
Environments which typically produce the largest errors include railroad yards, areas around electrical
substations, and sites near structures containing large amounts of steel or iron, such as bridges or large
buildings.
To help alleviate this azimuth error, the azimuth scan feature scans an azimuth range about the target
azimuth and seeks the strongest signal. This feature is explained in full in section 2.1.1.2.2.3.3.
The RC4600 uses 16-bit resolvers, or 25- bit optical encoders to sense azimuth and elevation position.
The 16-bit sensors offer a resolution of 0.0055°, where the 25-bit optical encoders offer a resolution of
0.00001°. It is important to make sure that the proper sensor is used for the application.
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