S 745-003
(2)
Push the TEST button on the front panel of the WBC.
(a)
Make sure that the WBC shows these test displays: 1) ++++++++ ++++++++ 2) XXXXXXXX XXXXXXXX 3) OOOOOOOO OOOOOOOO 4) ........ ........
NOTE:____Each test display shows for approximately 5 seconds. Then the WBC shows TEST IN PROGRESS for approximately 20 seconds.
(b)
Make sure that the WBC shows NO FAULTS.
NOTE: The NO FAULTS display goes out of view after
____ approximately 8 seconds.
S 865-004
(3) Remove electrical power if it is not necessary (AMM 24-22-00/201).
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A
747-400 MAINTENANCE MANUAL
TASK 31-41-00-825-005
3. Weight and Balance System - Calibration (Recommended)
_____________________________________________________
A. General
(1)
Use this procedure to calibrate the weight and balance system after landing gear replacement or overhaul.
(2)
During the calibration procedure you will collect data, calculate calibration data, and put the calibration data into the calibration module. You will also make a written record of the calibration data.
(3)
Then, you will find the zero values for the load sensors. To find the zero values, you must set the WBC to 100% autozero mode, let the airplane make at least one flight, and then read the zero values.
(4)
You will then collect four sets of data from the scales and the WBC.
(a) You will collect wheel weights from the scales and sensor counts from the WBC. Each time you read the weight on a wheel, you must read the counts for the adjacent load sensor at the same time.
NOTE: Wheel weights must be recorded in pounds (lbs.).
____
NOTE: Counts are values retrieved from the 16-bit A to D
____ converter in the WBC. Counts have a range of 0 to 65535.
(b) The first, third, and fourth sets of data are collected at normal strut pressures. The second set of data is collected at low wing landing gear strut pressures. Between the third and fourth sets of data, you will decrease and then increase the strut pressures of the body landing gear to prepare the WBC for the fourth data collection.
(5)
From the zero values and the four sets of data you will calculate the span and offset values for each load sensor.
(6)
You will use the WBC to read the load sensor resistance values. (The WBC uses resistance data to correct for temperature variation.)
(7)
You will use the WBC to put this data into the calibration module:
(a)
The calculated span and offset values.
(b)
The load sensor resistance values.
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A
747-400
MAINTENANCE MANUAL
(8)
You will do a check to make sure that the calibration is correct. Finally, you will make a written record of the calibration data.
(9)
A software calibration procedure with instructions is available directly from Honeywell. That procedure lets you record and calculate calibration data automatically. You can also keep the data for each airplane in a digital format. Speak to the Honeywell Customer Support Engineering Representative for the Weight and Balance System to get that procedure.
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