If the accuracy of the GPS position is not within the limits set, a "Low Accuracy GPS" message is displayed.
The AccuGrade System has three modes of accuracy available.
- Fine
- Medium
- Coarse
Each mode has a GPS error limit. The GPS error limit is defined to suit the application or project.
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.
GPS Position Error
The accuracy of a GPS position varies according to many different conditions. An RTK position is normally accurate enough for construction work. However, this is not always the case.
When a GPS antenna is placed in a stationary position and the position output 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.
The GPS error is an estimate of the amount of noise in the GPS positions.
The Role of the GPS Receiver
The satellites are above the antenna so the horizontal and vertical accuracies are different. The vertical position is less accurate than the horizontal position. You can display vertical position error and horizontal position error as text items. Refer to "GPS Accuracy Mode Text Items" for more information.
Blade guidance will only occur when the GPS accuracy for the antenna position is within the GPS error limit set for the GPS Accuracy Mode.
GPS Accuracy Mode Text Items
Three text items that are related to GPS accuracy mode are available for display.
- The "H. GPS Err." text item shows the GPS error in the horizontal plane.
- The "V. GPS Err." text item shows the GPS error in the vertical plane.
- The "GPS Acc. Mode" text item shows the currently selected GPS Accuracy Mode.
The "H. GPS Err." text item and the "V.GPS Err." text item change color in order to indicate the current GPS error relative to the configured GPS Error Limit. The color coding that is used is shown in table 1.
| Text Color | GPS Error Indication |
| Black | The GPS error is within 90% of the GPS error limit. |
| Blue | The GPS error is within 10% of exceeding the GPS error limit. |
| Red | The GPS error has exceeded the GPS error limit. |
Setting the GPS Accuracy Mode and Limits
The operator can select a GPS Accuracy Mode. You can change the Accuracy mode in Normal mode, but you must be in Service mode in order to change the GPS Error Limits.
Perform the following steps in order to access the "GPS Accuracy Mode" dialog.
- Turn the AccuGrade System on.
- From any guidance screen, press the "GPS" Soft Key.
- Press the Change Mode Soft Key (6) in order to swap between the following modes: Fine Accuracy, Medium Accuracy and Course Accuracy.
 | |
| Illustration 1 | g01262119 |
- Press "OK" in order to confirm the settings, or "ESC" in order to exit without saving.
Note: If you press "ESC", you are asked to confirm that you do not want to save any changes.
Editing The GPS Accuracy Modes
The AccuGrade System will need to be in Service Mode in order to edit the limits for the GPS Accuracy Mode.
- Turn off the Display.
- Press and hold the "OK" key when powering up the Display.
Note: Hold the "OK" key until the splash screen is displayed.
- Select the "GPS" Soft Key from any guidance screen.
- Press the "Edit Modes" Soft Key.
The "GPS Accuracy Mode Settings" dialog appears. This is shown in Illustration 3.
Note: By default, the "Edit Modes" Soft Key is only available when the AccuGrade System is started in Service mode.
 | |
| Illustration 2 | g01262115 |
- The group box within the "GPS Accuracy Mode Settings" dialog is labeled in order to indicate the GPS accuracy mode that is currently selected for change.
Use the "Fine Mode" Soft Key, the "Medium Mode" Soft Key, or the "Coarse Mode" Soft Key in order to select the GPS accuracy mode that you wish to change.
 | |
| Illustration 3 | g01262113 |
- Use the arrow keys in order to enter a value in the "GPS Error Limit" field. The GPS Error Limit defines the maximum allowable GPS error for the selected GPS accuracy mode.
- In order to set the GPS Accuracy mode to Unused, press the "Set Unused" Soft Key or enter a GPS Error Limit of 0.
Note: When the GPS Error Limit is set to Unused for a particular mode, the mode is no longer available to the operator for selection.
- In order to set the field to the default value press the Soft Key ("Default Set 0.050"). The limit value on the Soft Key ("Default Set 0.050") changes depending on the system Units and the GPS Accuracy Mode selected for change.
- In order to set the GPS Accuracy mode to Unused, press the "Set Unused" Soft Key or enter a GPS Error Limit of 0.
- Press the "NEXT" key in order to enter the "Allow Automatics" field.
- Press the arrow keys in order to toggle between "YES" and "NO".
This setting will allow the use of automatics in the selected GPS accuracy mode.
- Press "OK" in order to confirm the settings. Press "ESC" in order to exit without saving.
Note: If you press "ESC", you are asked to confirm that you do not want to save any changes.