CAMSHAFT-REAR 4P8434 - Caterpillar

The Global Positioning System (GPS)
GPS is a system of satellites that orbit the earth two times per day at very high altitudes. The radius of the orbit is approximately 26600 km (16528 miles). GPS was set up by the government of the United States. GPS provides precise timing and positioning to users anywhere at no charge for 24 hours per day.In general terms, a GPS receiver computes a position that is based on radio signals that are received from several different satellites. The satellites have very precise clocks. The timing of the signals is very accurate. The GPS receiver calculates the relative distance to each of the satellites. This calculation is based on the travel time of the signal and the speed of light (speed of the signal). The receiver then uses these distances in order to calculate the receiver's location on earth.As a broadcast only radio system, GPS supports an unlimited number of users. The broadcast frequencies penetrate clouds, rain, and snow. GPS can accurately guide operations in fog or dust. Also, GPS guides operations at night. There are different levels of precision and accuracy that are available from GPS. These levels depend on the GPS receivers and the methods that are used.There are four basic levels of GPS position accuracy."Autonomous" - 10 m (30 ft) to 15 m (50 ft)"DGPS" - 0.3 m (1.0 ft) to 1.0 m (3.0 ft)"RTK Float" - 0.2 m (0.7 ft) to 1.0 m (3.0 ft)"RTK Fixed" - .02 m (.07 ft) to .03 m (.10 ft)Illustration 1 shows the GPS levels of position accuracy.
Illustration 1 g01015622
GPS levels of position accuracy (1) "Autonomous" (2) "DGPS" (3) "RTK Fixed" (4) "RTK Float"The method that is used for machine grade control in construction is the same as that used by surveyors for "stakeout" in construction. The method is called "Real-Time Kinematic" (RTK) GPS.In order to produce RTK positions, two GPS receivers are required. One receiver is known as the GPS base station. This receiver is fixed in one place. The other GPS receiver is known as the "rover". This receiver can be stationary or mobile.The base station communicates to the "rovers" through a wireless data link with a radio. Illustration 2 shows this setup.Both the GPS base station and the GPS "rover" receivers make observations (measurements) of the GPS signals at the same time. The base station broadcasts the observed information together with the location and other information across the data radio link to the "rover". The "rover" then combines the data from the "rover" and the base station in order to compute a very accurate position relative to the base station.One base station will support an unlimited number of "rovers", provided that the "rovers" are within 20 km (12.4 miles) of the base station. Normally, the range of the data radio link is the more limiting factor. You can use radio "repeaters" in order to extend the radio coverage.The 900 MHz radio is recommended in areas that have the 900 MHz band. The