Document ID: chunk:federal_register_of_legislation:F2015C00542:reg:254:p13
Version: federal_register_of_legislation:F2015C00542
Segment Type: reg
Provision Reference: reg 254 (pt 13/18)
Character Range: 133532–136664

negative.

              9.2.1.1.3. Optical distortion at a point M: The optical-distortion maximum for all directions M-M' from the point M.

Figure 6

Diagrammatic representation of optical distortion

       Notes:

                        = 1 - 2,  i.e. the optical distortion in the direction M-M'.

                       x = MC i.e. the distance between two straight lines parallel to the direction of vision and passing through the points M and M'.

              9.2.1.2. Apparatus

               This method entails the projection of an appropriate slide (raster) onto the display screen through the safety glazing being tested. The change caused in the shape of the projected image by the insertion of the safety glazing in the line of light provides a measure of the distortion.

               The apparatus shall comprise the following items, arranged as shown in Figure 9.

              9.2.1.2.1. Projector, of good quality, with a high-intensity point light source, having for example the following characteristics:

               focal length at least 90 mm,

               aperture approximately 1/2.5,

               150-W quartz halogen lamp (if used without a filter),

               250-W quartz halogen lamp (if a green filter is used).

               The projector is shown schematically in Figure 7. A diaphragm of 8 mm in diameter is positioned approximately 10 mm from the front lens.

Figure 7

Optical arrangement of the projector

              9.2.1.2.2. Slides (rasters) consisting, for example, of an array of bright circular shapes on a dark background (see Figure 8). The slides shall be of sufficiently high quality and contrast to enable measurement to be carried out with an error of less than 5 per cent.

               In the absence of the safety glazing to be examined, the dimensions of the circular shapes shall be such that when the circular shapes are projected they form an array of circles of diameter

               , where x = 4 mm (see Figures 6 and 9).

Figure 8

Enlarged section of the slide

Figure 9

Arrangement of the apparatus for the optical distortion test

              9.2.1.2.3. Support stand, preferably one permitting vertical and horizontal scanning, as well as rotation of the safety glazing.

              9.2.1.2.4. Checking template for measuring changes in dimensions where a rapid assessment is required. A suitable design is shown in Figure 10.

Figure 10

Design for a suitable checking template

              9.2.1.3. Procedure

              9.2.1.3.1. General

               Mount the windscreen on the support stand (paragraph 9.2.1.2.3.) at the designed rake angle. Project the test image through the area being examined. Rotate the windscreen or move it either horizontally or vertically in order to examine the whole of the specified area.
              9.2.1.3.2. Assessment using a checking template

               When a rapid assessment with a possible margin of error of up to 20 per cent is sufficient, calculate the value of A (see Figure 10) from the limit value L for the change in deviation and