Document ID: chunk:federal_register_of_legislation:F2015C00542:reg:254:p17
Version: federal_register_of_legislation:F2015C00542
Segment Type: reg
Provision Reference: reg 254 (pt 17/18)
Character Range: 144883–147848

angle of n minutes of arc at a point situated at x metres (Figure 11(b)), where

                 n is the limit value of secondary-image separation,

                    x is the distance from the safety glazing to the target (not less than 7 m),

                 D is given by the formula: D = x . tg n

               The illuminated target consists of a light box, approximately
              300 mm x 300 mm x 150 mm, whose front is most conveniently constructed of glass masked with opaque black paper or coated with matt black paint.

               The box shall be illuminated by a suitable light source. It may be convenient to use other forms of target, such as that shown in Figure 14. It is also acceptable to replace the target system by a projection system and to view the resulting images on a screen.

              9.3.1.1.2. Procedure

               Mount the windscreen at the specified rake angle on a suitable stand in such a way that the observation is carried out in the horizontal plane passing through the centre of the target. The light box shall be viewed in a dark or semi-dark room, through each part of the area being examined, in order to detect the presence of any secondary image associated with the illuminated target. Rotate the windscreen as necessary to ensure that the correct direction of view is maintained. A monocular may be used for viewing.

              9.3.1.1.3. Expression of results

               Determine whether,

               When target (a) (see Figure 11(a)) is used, the primary and secondary images of the circle separate, i.e. whether the limit value of n is exceeded, or

               When target (b) (see Figure 11(b)) is used, the secondary image of the spot shifts beyond the point of tangency with the inside edge of the circle, i.e. whether the limit value of n is exceeded.

Figure 11

Dimensions of targets

Figure 12

Arrangement of apparatus

Figure 13

Apparatus for collimation-telescope test

              9.3.1.2. Collimation-telescope test

               If necessary, the procedure described in this paragraph shall be applied.

              9.3.1.2.1. Apparatus

               The apparatus comprises a collimator and a telescope and may be set up in accordance with Figure 13. However, any equivalent optical system may be used.

              9.3.1.2.2. Procedure

               The collimation telescope forms at infinity the image of a polar co-ordinate system with a bright point at its centre (see Figure 14).

               In the focal plane of the observation telescope, a small opaque spot with a diameter slightly larger than of the projected bright point is placed on the optical axis, thus obscuring the bright point.

               When a windscreen which exhibits a secondary image is placed between the telescope and the collimator, a second, less bright point appears at a certain distance from the centre of the polar co-ordinate system. The