AccuGrade® Version 11 Compaction GPS Mapping and Measurement System Caterpillar

The GPS Accuracy mode offers the following advantages.

• Allows you to specify the GPS error limits that are suitable for your application or project

• Provides confidence that you are working within the GPS error limits that you have specified

• Increases the efficiency of the machine use by allowing the operator to quickly switch GPS Accuracy Modes so that different applications can be carried out

Note: GPS Accuracy Modes and GPS error limits apply to the GPS antenna position only. GPS error limits do not take into account Measure-up errors. GPS error limits do not take into account base station coordinate errors.

The AccuGrade System has the following three available modes of accuracy:

• Fine

• Medium

• Coarse

Each mode has an associated error limit. The error limit is defined to suit the application or the project.

Note: Satellite-based Augmentation Systems (SBAS) can be used when Coarse Mode is selected. Refer to Systems Operation, "General Information" for additional SBAS details.

Your supervisor sets the limit for each mode. Your supervisor sets each mode to suit the type of work that you are doing. If the GPS error estimate exceeds the limits that are defined for the selected mode, then a "Low Accuracy GPS" message is shown on the Display.

Your supervisor can also deactivate the modes. For example, the limits for Fine mode are set for finish work. If GPS accuracy is not within the tolerance that is set for Fine mode, do not change into Coarse mode and continue working on your final surface.

Perform one of the following actions to continue:

• Wait for the GPS accuracy to improve. Continue in Fine mode.

• Change the GPS Accuracy mode. Continue working on an area that does not require Fine mode GPS accuracy.

• Change the GPS Accuracy mode. Raise the vertical offset in order to leave the constructed surface high. Return to the area when the GPS accuracy has improved and Fine mode operations are allowed. This allows you to continue working on the same area of the design and not to overcut the final design surface.

GPS Position Error

The GPS error is an estimate of the amount of noise that is in the GPS positions. The accuracy of a GPS position varies according to many different conditions.

Refer to Systems Operation, "General Information" for additional details about RTK.

When a GPS antenna is placed in a stationary position and the output of the position is monitored, there are small changes in the position. The position change is caused by noise in the solution. This results in a small error in the GPS position.

GPS Accuracy Mode Text Items

Three items that display the current accuracy level of the GPS can be displayed on the guidance views:

• H. GPS Err.

• V. GPS Err.

• GPS Acc. Mode

The color of the item shows whether the current error is within the selected limits.

• Black - The error is less than 90 percent of the limit defined for the GPS accuracy mode.

• Blue - The error is approaching the defined limit.

• Red - The error exceeds the defined limit.

GPS Dialog

Illustration 1 shows the physical layout of the AccuGrade Display. Refer to this Illustration for the location of the keys that are discussed within this section.

Illustration 1	g01290651
(1) LCD screen (2) Soft key labels (3) Soft keys (4) Next key (5) Escape key (6) Zoom-in key (7) Access door for data card (8) Menu key (9) Arrow keys (10) OK key (11) Zoom-out key (12) Power key

Perform the following steps in order to configure the "GPS" dialog and set the GPS accuracy mode.

1. From any guidance screen, press the Menu key (8). The "Setup Menu - Configuration" screen appears.

2. Scroll to the "GPS Accuracy" option. Use the arrow keys (9) .

3. Press the OK key (10). A "GPS" dialog appears. The dialog shows the current settings for the GPS.

Note: You set the limits by using the "Edit Modes" soft key (16). This is not normally a function that is performed by an operator. These limits should only be changed at the request of the on-site manager. Refer to Illustration 2.

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Illustration 2	g01381358
Typical example of a GPS accuracy mode dialog (13) Current accuracy icon (14) Current accuracy description and icon (15) Current error limit (16) Edit Modes soft key (17) Change Mode soft key

4. Press the "Change Mode" soft key (17) in order to move between Fine, Medium, and Coarse accuracy modes. Refer to Illustration 2.

   The recommended mode for the AccuGrade System is "Fine". This mode uses an "RTK Fixed" solution for positioning. If the on-site supervisor allows SBAS positions to be used, perform the following steps to configure this option.

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   Illustration 3	g01377249

   1. Press the "Change Mode" soft key (17) until the "GPS accuracy mode:" displays "Coarse".

   2. Verify the setting in the "Use SBAS Connections:" field.

      Yes - SBAS is enabled. No action is required. Continue at Step 5.

      No - SBAS is not enabled. Continue at Step 4.c.

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   Illustration 4	g01377251

   3. Press the "Edit Modes" soft key (16). The "GPS Accuracy Mode Settings" dialog appears. The "GPS error limit:" field is highlighted.

   4. Set the value in the field. Use the arrow keys (9).

      Note: For SBAS to work correctly, this value should be greater than the SBAS error of 2 m (6.6 ft). These limits should only be changed at the request of the on-site manager.

   5. Press the Next key (4). The "Allow SBAS positions:" field is highlighted.

   6. Change the value to "Yes". Use the arrow keys (9) .

   7. Press the OK key (10). The "GPS" dialog appears. The new values appear in the dialog.

5. Press the OK key (10). The setup is saved. The dialog closes. The "Setup Menu – Configuration" screen appears. The changes take effect immediately.

6. Press the Escape key (5). A guidance screen appears.