Problem:

Certain AP-1050 and AP-1000 Asphalt Pavers equipped with sonic non-contacting grade and slope control systems (manufactured by AGTEK Development Company, Inc.) have experienced problems with the performance of the system. Factors that have affected the control system include (1) system software calibrations, (2) heat, (3) averaging, and (4) ramping and ramping distance.

Solution:

Preliminary investigation by the Product Support Department has determined that the cleanliness of the paver hydraulic systems, possible residual or static noise in the paver electrical systems, and reliability of the servo valve operation have NOT been identified as significant causes for performance problems in the field.

A joint effort between the Product Support Department and AGTEK to troubleshoot the system has identified several potential problem areas which might affect the operation and application of the AGTEK system. AGTEK has made some modifications to the system software and revised some of the performance settings to address these identified problems.

1.Software Revision (r3.3)

This software revision introduced the capability to calibrate "valve offset" in servo valves, where it had no effect before. Follow the instructions given in the AGTEK "Paver Control System Four Technician's Menu Performance Settings" manual (Part No. 7010-0128-Rev. B). This software revision improves servo operation and response.

NOTE: The earlier manual (Rev. A) may also be used, but disregard the statement about servo valves on page 2-2 of the manual.

Refer to Page 3 of this Technical Information Bulletin for information on determining system software revision.

2.Heat

The AGTEK tracker can be affected by temperature variations, resulting in poor performance under certain circumstances. Large or rapid air temperature fluctuations in the area of the tracker sonic pulses impair tracker capabilities. If the air temperature remains fairly consistent between the bottom of the tracker and the reference point, the temperature compensating bail will adjust for these minor changes. When temperature fluctuations are large, or if channeled air flow is directed only above or below the temperature compensating bail, a false temperature correction will result.

The system could also go into a "stand-by" mode. When this occurs, the auto light above the control box adjustment knob will go out, and come back on when the temperature compensation feature brings the reference point back into the Working Window. To avoid these problems, we are changing the recommended setup height to 355-380 mm (14-15 in) from the reference point to the bottom surface of the tracker [125-150 mm (5 ± 6 in) from the reference to the compensating bail]. This minimizes the possibility of channeled air flow passing only above or below the compensating bail, causing false temperature corrections.

Location of the tracker is another area of concern. The tracker should be positioned to avoid heat generated by the paver, asphalt mix, or other foreign sources.

3.Averaging

When using the AGTEK system with an averaging ski, be sure that the tracker is sensing the stringline and not the averaging ski beam. If the tracker senses the beam, the control uses this reference and averages it. That action results in a false correction.

AGTEK has developed an r3.4 software revision, which only allows the control to average within the Working Window. The software change eliminates the potential for a false correction. On AGTEK units that have the r3.3 software revision or earlier, any false reading will be averaged and could significantly affect the average reading. Therefore, the averaging calibration should be set to "1" if this problem occurs. The default calibration setting is "10". The "10" setting should be used with the r3.4 software revision.

4.Ramping And Ramping Distance

Both of these calibrations correlate with Gain and can be recalibrated for faster or slower tow point cylinder response. Also, the Ramping can be turned completely off, which is indicated by "0". The recommended Ramping calibration seems to work well at paving speeds less than 12.2 meters (40 feet) per minute.

For faster paving speeds, ramping can be reduced to enhance control and machine performance. Ramping speed should be set at 1.5 to 2.5 seconds for normal paving conditions. This is contrary to AGTEK's recommendation of 4 seconds.

A larger Ramping (time) setting delays the control's response. It has been found that grade is better maintained when the Ramping Distance is set at ".05". However, this setting, as well as Ramping and Averaging, are application dependent and should be calibrated to operator preference during initial machine startup. The default setting for Ramping is "4" seconds and the default setting for Ramping Distance is ".07".

Accessing Calibration Features

Identify your system Revision Code by turning the power to ON to the elevation (GRADE) position. The first set of code numbers that flash on the screen indicate the software Revision Code, for example r3.1. The second set of code numbers indicates the electrical cable installed between the paver tractor and the control system junction box. Check to make sure the correct cable is installed. Caterpillar machines, which are equipped with proportional grade and slope servo controls, utilize a cable coded "C24". To access the operator's and technician's performance settings menu, refer to the Operator's and Technician's Manual.

The system features for each of the existing revisions are described as follows:

Revision r2.1 (January 1993) -Operating Functions are described in the Operator's Manual.

Revision r2.2 (February 1993) -Changed the code so that auto mode could be entered from survey mode. When returning to manual, the control box will be in control mode and not survey mode.

Added a code to allow use with the wide range slope sensor.

Revision r2.3 (March 1993) -Software was changed to allow grade adjustment with the knob on the former 9140 Tracker.

NOTE: A limited number of Caterpillar Pavers were shipped with this revision of AGTEK grade and slope control system.

Revision r3.1 (August 1993) -Technician's menu was added. This allows a dealer or field technician to access and make changes to the following:

1. Functions already existing in the control box include ramping, ramping distance, averaging, frequency, deadband, and units.

2. New Functions: stringline function (turns the Working Window ON or OFF), lockout, configuration, and temperature cutout.

The Gains were adjusted to be less sensitive. The Gain on earlier boxes had to be set very low.

Changed the display for inch mode function. Numbers under 19.99 are displayed with two decimal places instead of one decimal place and alternating decimal place.

NOTE: This is the most common revision that has been shipped with Caterpillar machines equipped with AGTEK grade and slope control systems. R

Revision r3.3 (January 1994) -Valve offset calibration was applied to servo valve operation, configuration C24. Also, adjustment (ADJ) of Working Window size was added to stringline function (STR) of the technician's menu.

Revision r3.4 (May 1994) -Changed the Sonic Tracker averaging code so that only measurements inside the Working Window are averaged.

Available Reference Manuals And Software Update Revisions

The following reference manuals are available:

Paver Control System Four Manual (P/N: 7010-0118)

Paver Control System Four Getting Started Manual (P/N: 7010-0140)

Getting Started Quick Reference pocket guide (P/N: 7010-0141)

Technician's Menu Performance Settings (P/N: 7010-0128)

For ordering information and availability for these manuals and the latest revision control system software, contact AGTEK directly at the following address:

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