Usage:
Introduction
Certain Telescopic Material Handling (TMH) vehicles have the 838797 Load Indicator Group installed. The load indicator group consists of a strain sensor, a display unit and associated wiring, and mounting hardware. When the load indicator group is installed at the factory, the strain sensor is bonded to the machine frame and a special procedure is used to set up and calibrate the display unit.
The 838843 Display Unit and the 844241 Strain Sensor Group cannot be repaired. If either component is found to be defective, it is essential that correct installation and calibration procedures are used when installing new parts.
This Special Instruction describes the correct procedures for installation of a new 844241 Strain Sensor Group and the correct procedures for calibration of the load indicator system. This procedure must be followed whenever a new 844241 Strain Sensor Group or 838843 Display Unit is installed.
Do not perform any procedure, outlined in this publication, or order any parts until you read and understand the information contained within.
Reference: Service Manual and Parts Manual.
Strain Sensor Installation
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A raised boom can fall causing injury or death if a hydraulic component fails. Install the boom lock or blocks before working under a raised boom. |
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NOTE: The frame must be dry and at a minimum temperature of 15°C (59°F) shop temperature. Localized heating must not be applied to achieve this temperature.
The strain sensor is bonded to steel mounting blocks which are welded to the left side of the machine frame, adjacent to the boom raise cylinder anchor.
1. Disconnect the old strain sensor cable from the display unit cable (located under the dash panel), and remove the strain sensor.
2. Clean the mounting blocks thoroughly, ensuring that all traces of adhesive are removed from the top faces.
3. Use a straight edge and a 0.05 mm (0.002 in) feeler gauge to check the alignment of the top faces of the blocks.
NOTE: File the blocks if necessary until the top faces are aligned within 0.05 mm (0.002 in).
4. Clean the screw holes by using an M8 tap. Be sure that the top faces of the mounting blocks are clean and dry. Degrease the mounting block faces.
5. Route the new strain sensor cable to the dash panel housing and connect it to the display unit cable.
844241 Strain Sensor Group. (A) Transit plate. (B) Steel blocks.
6. Disassemble the 844241 Strain Sensor Group and discard transit plate (A) and steel blocks (B). Remove the protective vinyl tape from the new strain sensor mounting faces, and degrease the mounting faces. Do Not scrape the mounting faces.
NOTE: The mounting faces are on the side of the sensor with the raised digits in the center.
7. Apply a thin coating of 985214 Adhesive (Loctite 638®) to the faces of the mounting blocks and to the mounting faces of the sensor.
NOTE: The sensor is shown correctly installed in the following illustration.
Strain Sensor Installation.
8. Install sensor (1) and tighten capscrews (2) hand tight only. Wait twenty minutes and then tighten the capscrews evenly, first to a torque of 20 N·m (15 lb ft), and then to a torque of 35 N·m (25 lb ft). Allow four hours of setting time before operating the machine.
9. Calibrate the system.
Calibration
The load indicator system must be calibrated whenever a new 844241 Strain Sensor Group or 838843 Display Unit is installed.
No special equipment is required to perform the calibration. Do not apply any test weights or loads to the forks of the machine while performing the calibration.
The three calibration controls are located under a cover at the left side of the display unit, and are adjusted with a small screwdriver.
The following items must be followed while performing the calibration procedure.
- * During system calibration, the person making the adjustments should remain on the machine. Other persons should not mount any part of the machine and no loads should be placed on the forks.
- * During calibration the engine is shut down and the start keyswitch is turned back to the "ON" position each time the boom is repositioned. This is to simplify adjustment by eliminating engine vibration.
- * When the start keyswitch is turned to the "ON" position, the load indicator system will display a start up routine consisting of lamp and LED (light emitting diode) patterns and an audible alarm. This routine takes ten seconds. No adjustments must be made until the start up routine is completed.
- * There are 14 LED's on the display unit illuminating scale. Starting from the left, the first eight are green, the next five are amber, and the last one is red. During calibration the green LED's illuminate in what may appear to be a random manner. In fact, each combination of illuminated LED's represents a binary number. However, it is not necessary to understand the binary numbering system to perform the calibration.
- * During calibration the engine is shut down and the start keyswitch is turned back to the "ON" position each time the boom is repositioned. This is to simplify adjustment by eliminating engine vibration.
Follow the instructions given and the correct calibration should be achieved.
1. Position the machine on a flat, level surface with boom fully retracted. Set the forks level at 150 mm (6.0 in) above the ground with no load. Stop the engine and turn the start keyswitch to the "ON" position.
Display Unit. (3) Cover. (4) Mode Pushbutton. (5) Power Lamp. (6) Illuminating Scale LED's. (7) Zero Preset. (8) Zero Lamp. (9) Span Preset. (10) Zero Button.
2. Remove cover (3) from the display unit and carefully press the mode pushbutton (4) three times. Power lamp (5) will flash and illuminating scale (6) LED's will illuminate in a random pattern.
3. Turn zero preset (7) fully to the right, and then turn slowly to the left until only zero lamp (8) and the first amber LED on illuminating scale (6) are illuminated.
4. Carefully press mode pushbutton (4) once. Power lamp (5) will illuminate continuously and illuminating scale (6) will display a random pattern which must include the last amber LED.
Zero Preset LED Pattern.
5. Turn zero preset (7) slowly to the left until illuminating scale (6) displays the pattern shown above with zero lamp (8) continuously illuminated.
6. Start the engine and fully extend the boom. Position the forks 150 mm (6.0 in) above the ground. Stop the engine and turn the start keyswitch back to the "ON" position.
7. Carefully press mode pushbutton (4) once. Power lamp (5) will illuminate continuously, and illuminating scale (6) will display a random pattern which must include the last amber LED.
8. Turn span preset (9) fully to the right, then turn it slowly to the left to obtain the illuminating scale pattern which matches the machine duty chart number as shown in the chart.
9. Start the engine and fully retract the boom. Position the forks 150 mm (6.0 in) above the ground.
10. Stop the engine, turn the start keyswitch to the "ON" position, and press mode pushbutton (4) once. Check the illuminating pattern. The pattern should be the same as the illustration in Step 5.
If it is not, adjust zero preset (7) to obtain the correct pattern.
NOTE: A small adjustment (right or left) should reestablish the correct pattern.
Repeat Step 6.
Press mode pushbutton (4) once and check that the appropriate LED pattern from the chart is displayed again.
If it is not, adjust span preset (9) to obtain the correct pattern.
NOTE: A small adjustment (right or left) should reestablish the correct pattern.
11. Fully retract the boom and position the forks level 150 mm (6.0 in) above the ground.
12. Stop the engine, turn the start keyswitch "ON", and press mode pushbutton (4) once.
13. Press zero button (10) once. For the next five seconds, the audible alarm will sound intermittently and the zero lamp will be illuminated continuously. During this five second period (while the alarm is still sounding) press the zero button once again to lock the calibration.
14. The system will now acknowledge completion of the calibration by sounding the audible alarm continuously for a short period.
15. If the five second period of intermittent alarm operation is missed (the zero button is not pressed to lock the calibration), or if the "acknowledge" signal is not given, turn the keyswitch "OFF" and then "ON" to restart the five second period. Press the zero button during the five second period and listen for the "acknowledge" signal.
16. The load indicator system is now calibrated and ready for use.
NOTE: If the machine duty chart number does not appear above, refer to your Caterpillar dealer for more current information.