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Precision In-Line (PIL) Picture Tube
Precision In-Line (PIL) Picture Tube as the name suggests has three guns that are aligned precisely in a horizontal line. In this, all three guns are aligned in a horizontal line or row. The inline gun configuration helps in simplifying convergence adjustments. The guns are mounted in the horizontal plane with the green gun at the center, red and blue guns are on the left and right as shown in the figure below.
Each gun in the PIL picture tube has its own cathode control grid, screen grid and focus grid.
The aperture mask has vertical slots through the converged beams pass to strike the corresponding colour phosphor stripes. These tubes are design with such precision that they are almost self converging and require hardly any convergence adjustments.
The improved gun design has enabled excellent focus to be maintained with a small spot size for high resolution in the picture. The shadow mask is positioned about 1 cm behind the tube screen.
Shadow Masks
The gun and the mask structure of Precision In-Line (PIL) Picture Tube.
The PIL picture tube carries with it the deflaction yoke and megnet assembly for purity and convergence, factory adjusted and bonded on the tube neck. The deflection yoke used a torroidal yoke having precision wound coils and is less bulky.
Convergence Errors
since the three raster should be accurately superimposed on each other, it’s give some constraints on the distribution of the deflection. Non optimum distribution of field produces the convergence error as the screen is nearly flat surfaces.
There are two kinds of colour errors are:
- Astioniatism effect
- Comma effect
Astigmatism Effect
It is clear from the figure shown below, that with the uniform field, the rays from a vertical row of points (PGQ) converge to produce a vertical focal line on the screen but the rays from a horizontal point (RGB) converge beyond the screen. This effect is referred to as astigmatism and results in convergence error. In PIL picture tube, beams RGB emerge only from a horizontal line and so vertical astigmatism has no effect.
To eliminate horizontal astigmatism, the horizontal focus should be a point on the screen but not a line for any deflection. Because of the change in the shape of the deflection field, opposite changes in horizontal and vertical astigmatism occur. Suitable field adjustments are required to make sure that the beams coming from inline guns in horizontal line coverage should be at the same point on the screen irrespective of the deflection angle.
Comma Effect
Due to the non-uniformity of the deflection field, all the beams are not deflected by the same amount. The green beam deflects less as compare to the other two beams. Such a distortion is known as the Comma effect and results in misconvergence of the beams as shown below.
Advantages of Precision in-line
- The PIL tubes are very efficient that mean higher electron transparency (50%) and needs fewer convergence adjustments.
- No needs of vertical convergence, only horizontal convergence is required at the stage of manufacturing.
- Focus is sharp all over the screen.
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