-
brightness generation
-selection of normal and red gun test brightnesses. Note that a separate relative manual brightness control is provided for the WXR image, and only for the NDs. If a WXR image is displayed on the PFD , it will be subject to the general brightness control of the whole display.
(c) G1 Amplifier When failures are detected by the CRT protection circuit, it sends a binary signal to the CRT G1 grid inhibition circuit. The CRT is then cut off to preserve it from destruction. This function is achieved by inserting a G1 amplifier circuit between the CRT protection circuit and the grid. This circuit effectively cuts off supply to the grid in the event a fault is detected.
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(d) Deflection and correction circuits
1_ Correction circuits
The correction circuits provide compensation for two types of
defaults:
- Pin cushion distorsion on the Y axes
- Linearity distorsion on both X and Y axes.
2 Deflection circuits
_ Considering the final purpose of this display unit, two types of scanning are used:
-Greek-type scanning with defocusing for the background colored areas (Sky/Ground on the PFD, weather radar on the ND, grey rectangles used on the various DUs to enhance the legibility of information (e.g. those used on the PFD for the SPD, ALT, V/S, HDG scales)
-Stroke Scanning for symbology.
On the CRT, the colored backgrounds are drawn with a speed of
5 mm/μs and the symbology is drawn at a speed from 0.625 mm/μs
to 1.25 mm/μs.
Deflection circuits are identical on X and Y channels.
A power saver circuit is used. This circuit saves the power
which is dissipated in the deflection amplifier power stage,
by modulating the voltage of the power supply, according to
the speed of the drawing.
The switching time of this circuit is less than 500 ms.
(e) Misconvergence correction Two types of adjustments are provided:
-Static convergence 3 pairs of beam benders are used to adjust the beam position on screen center
-Dynamic convergence Convergence coils are used to adjust the beam on a screen corner.
(f) Monitoring circuits These circuits monitor the deflection and color unblank inputs. In the event of a failure, these inputs are replaced by an internal test pattern producing a dedicated white pattern on the screen (diagonal line). In addition, these devices contain an orbiting circuit which makes the whole picture slightly move on the screen in a circular motion in order to avoid burning those phosphor elements which would be constantly striken for the display of fixed elements. The period of picture movement is about 30 seconds.
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(g)
Protection circuits The protection circuits are provided for phosphor protection and continuous self-test of the DU. They monitor the low voltage power supplies and the beam movements. Minimum programmable authorized beam speed : 0.625 mm/μs. In the event of a failure, the CRT is inhibited by G1 and the DU ANOMALY signal is positioned. A temperature switch detects any abnormal temperature rise. A thermo switch cuts off the power supply when internal temperature rises over a dangerous level. Line fuses : they protect the line against power supply input short circuit, and against eventual lightning strike effects.
(h)
Red color gun monitoring Basically the red color gun is controlled by internal DU circuitry, provided that the SG supplies the specific reserved color code. The DU sends back to the DMC, the DU beam test results, via the DSDL feedback line.
(4) Symbol generator
(a) General The Symbol Generator is designed around 3 VLSI circuits. Seven other LSI circuits have been specially designed to allow the implementation of the SG unit in the DU. The main functions of the SG are the following:
-
Drawing Program Control
-
Drawing Execution
-Color, Blanking and Brightness Control
-Information exchange Control with the DMC.
Main characteristics:
-the SG program memory is partly RAM and partly EEPROM. PFD, ENGINE and parts of the ND programs are memorized in the EEPROM area. Other programs in process are teleloaded from the DMC at each mode change via the 800 Kbit/s serial link DSDL
-current data are coming from the DMC via the serial link and stored in the SG Memory by Direct Memory Access without any decrease in the drawing speed. Feedback data from the DU to the DMC are also obtained by Direct Memory Access
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