1、AECMA STANDARD NORME AECMA AECMA NORM Edition approved for publication 30 September 2004 prEN 3475-705 Edition P 2 September 2004 Comments should be sent within six months after the date of publication to AECMA-STAN ICs: 49.060 Descriptors: ENGLISH VERSION Aerospace series Cables, electrical, aircra
2、ft use Test methods Part 705: Contrast measurement Will supersede EN 3475-7052002 Srie arospatiale Luft- und Raumfahrt Mthodes dessais Prfverah ren Cbles lectriques usage aronautique Partie 705 : Mesure de contraste Elektrische Leitungen fr Luftfahrtverwendung Teil 705: Kontrastmessung This “Aerospa
3、ce Series“ Prestandard has been drawn up under the responsibilify of AECMA-STAN (The European Association of Aerospace Industries - Standardization). It is published for the needs of the European Aerospace Industry. It has been technically approved by the experts of the concerned Domain following me
4、mber comments. Subsequent to the publication of this Prestandard, the technical content shall not be changed to an extent that interchangeability is affected, physically or functionally, without re-identification of the standard. After examination and review by users and formal agreement of AECMA-ST
5、AN, it will be submitted as a draft European Standard (prEN) to CEN (European Committee for Standardization) for formal vote and transformation to full European Standard (EN). The CEN national members have then to implement the EN at national level by giving the EN the status of a national standard
6、and by withdrawing any national standards conflicting with the EN. Electrical Domain I I Copytight 2004 O by AECMA-STAb Page 2 prEN 3475-705:2004 Foreword This standard was reviewed by the Domain Technical Coordinator of AECMA-STANS Electrical Domain. After inquiries and votes carried out in accorda
7、nce with the rules of AECMA-STAN defined in AECMA- STANS General Process Manual, this standard has received approval for Publication. Contents Page O 1 2 3 4 4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.2.7 4.2.8 4.2.9 4.3 4.3.1 4.3.2 4.3.3 4.3.4 4.4 4.5 Introduction Scope Normative referen ces Def
8、initions Requirements Preparation of samples Test equipment Components of the measuring device Equipment colour Photometer Illumination and viewing system Equipment design and measurement methodology Measurement spot size Measurement area Calibration Measurement tolerance Measurement process Precaut
9、ionary measures Picture definition Sample area Number and location of measurements Determination of contrast values Requirement 3 3 3 3 4 4 4 4 4 5 5 5 5 5 5 5 6 6 6 6 6 7 7 Page 3 prEN 3475-705:2004 O Introduction It is a requirement within the aerospace industry that all wires and cables within an
10、 aircraft electrical system are identified with a circuit identification code at regular intervals down the length of the wire. Various marking methods are used for marking these identification codes on to the surface of electrical wires or cables including ink based and laser based processes. The l
11、egibility of the markings is dependent upon the process used and the insulation medium. Minimum standards of contrast are required to facilitate reading back of the identity codes. 1 Scope This standard specifies the process to be applied for measuring the contrast of wire and cable identification m
12、arkings against the background of the unmarked wire insulation. It has been developed primarily to define a reproducible process of contrast value determination for use both to determine the intrinsic laser markability of wires at the time of manufacture or later, and to enable electrical wiring sys
13、tems manufacturers to ensure that the whole process of wire marking is carried out to the required standard. 2 Normative references This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in
14、 the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred t
15、o applies (including amendments). IS0 7724-1, Paints and varnishes - Colorimetry - Part 1: Principles EN 3475-706, Aerospace series - Cables, electrical, aircraft use - Test methods - Part 706: Laser markability IEC 15-2, Colorimetry TR 4543, UV laser wire marking systems for aircraft wire and cable
16、 identification 3 Def i n i ti ons For the purpose of this standard the following terms and definitions apply. 3.1 contrast the ratio of the difference in luminance between the marked and unmarked areas of the insulation divided by the luminance of the unmarked insulation 3.2 luminance the quantitat
17、ive measurement of the visible light reflected from a surface, in this case the wire or cable insulation 1) In preparation at the date of publication of this standard Page 4 prEN 3475-705:2004 3.3 laser laser is an acronym for Light Amplification by the Stimulated Emission of Radiation. Lasers are a
18、 source of intense monochromatic light in the ultraviolet, visible or infrared region of the spectrum. 3.4 ultraviolet (abbreviation UV) electromagnetic radiation in a wavelength range from approximately 200 nm to 400 nm 3.5 UV laser a laser that produces a beam of UV radiation 3.6 f I uence the ene
19、rgy density, measured in J cm- (Joules per square cm) of a single pulse of the laser beam, which, for the purposes of this document, is taken at the surface of the wire insulation or cable jacket 3.7 wavelength wavelength (A) is measured in nanometres, nm. 1 nm = IO- m. h = c/fwhere c is the velocit
20、y of light andfis the frequency 4 Requirements 4.1 Preparation of samples The wire or cable samples shall be identified in accordance with the applicable manufacturing instructions for the marking equipment. Where samples are to be UV laser marked this shall be done using the fluence specified in TR
21、 4543 or the relevant wire or aircraft manufacturers process specification if different. When determining the laser markability of wires, this shall be in accordance with EN 3475-706. Take a sample of the wire for marking. Before marking the wire ensure that the wire surface is clean and dry and fre
22、e from dust and dirt; if necessary wipe it clean using propan-2-01 (isopropyl alcohol). The surfaces of the samples shall be clean and without damage. The identification markings to be measured shall be even in colour and characters shall have well defined edges. Before starting measurements clean t
23、he surfaces with a soft, lint-free cloth, if required, to avoid distortion of test results by a roughened surface or “deposits”. 4.2 Test equipment 4.2.1 The measuring device shall comprise, at a minimum, a photometer, an illumination system and a purpose designed sample holder suitable for wire and
24、 cable. The whole system shall be designed to ensure that test results are not falsified by external influences. The photometer shall be designed to be stable and free from vibrations and to exclude the influences of external light and reflections from scattered light. Components of the measuring de
25、vice 4.2.2 Equipment colour The device for holding samples and any accessories and the equipment in the vicinity of the measurement area shall be matt black in colour to absorb scattered light. Page 5 prEN 3475-705:2004 4.2.3 Photometer The luminance shall be determined with a calibrated electrical
26、photometer, which shall incorporate a photopic filter to simulate the response of the human eye. The manufacturers instructions concerning the photometer working range and operating instructions shall be observed. The measurement sensitivity of the photometer shall be in conformity with IEC publicat
27、ion 15-2. 4.2.4 Illumination and viewing system The illumination system shall consist of two light sources of equal intensity (see Figure 1). The two sources may be two separate lamps or, preferably, two fibre light guides fed from a single lamp. The light from the sources shall overlap to illuminat
28、e a central spot on the sample at an angle of 45“ to the surface. The light cones shall illuminate the wire sample longitudinally along its length and in a manner to avoid the formation of shadows. The photometer must be installed to view the sample along the normal to the surface, .e. at go“, and a
29、bove the principal focus at a distance that depends on the objectives focal distance. It shall be adjusted during calibration and after every change of objective. If two separate lamps are used they shall be of identical power consumption and shall always be exchanged in pairs. The radiating light e
30、nergy and colour temperature of the lamps shall be compatible with the working range of the photometer, according to the manufacturers instructions. The spectral distribution of the light shall be close to artificial light specifications according to light standard A, IS0 7724-1. Only gas filled lam
31、ps with tungsten filaments shall be used. The colour temperature shall be (3 O00 k 500) K. The voltage supply for the lamps shall be insensitive to line fluctuations. A stabilised d.c. power unit shall be used. 4.2.5 To determine the contrast, measurements must be taken of the luminance from both ma
32、rked and unmarked areas of the insulation. Depending upon the contrast measurement equipment design, the photometer may be used either to take a series of individual point measurements sequentially or it may determine the contrast instantaneously by the simultaneous measurement of the luminance of a
33、ll the sample points of an area of the sample. If a point measurement system is used, sufficient points shall be sampled on both the marked and unmarked portion of the wire to ensure that a good average value of the reflectance of each is obtained. Equipment design and measurement methodology 4.2.6
34、Measurement spot size The maximum admissible diameter of the photometer measurement spot shall be not in excess of 75 % of the character stroke width. This is particularly important if using a point measurement system where spot sizes are typically relatively large. 4.2.7 Measurement area The contra
35、st shall be measured over a finite area to include a significant portion of the marked and the unmarked surface of the wire. It is important that spot measurements should not be made immediately adjacent to the edge of a character, either on the mark or the unmarked insulation, to avoid scattered li
36、ght from the adjacent area from interfering with the measurement. Area measurement systems should discriminate against such scattered light by suitable means. 4.2.8 Calibration The photometer shall be calibrated by use of a reference sample, e.g. ceramic tiles, of known reflectance, certified and tr
37、aceable to National Standards. The frequency of calibration shall be in accordance with the equipment manufacturers guidelines. 4.2.9 Measurement tolerance The measuring tolerance of the photometer shall be not more than 2 %. Page 6 prEN 3475-705:2004 4.3 Measurement process 4.3.1 Precautionary meas
38、ures There may be a danger from some illumination systems that they may cause the samples to heat up significantly. If this is the case then measurements should be taken without delay and the sample removed from the test area after the measurements have been taken. Contrast measurements shall not be
39、 taken in areas of the sample a) incorporating the wire manufacturers markings, b) for tape wrapped wires, in areas where the tapes overlap, or c) where there are visible inclusions, deformities or other surface irregularities, as these can all cause errors in the determination of the contrast value
40、 NOTE If checking for repeatability it is of the utmost importance to ensure that the same character of the same mark and the same position within the character are measured each time. Significant variations in contrast may occur otherwise. WARNING taken when interpreting the contrast results of so
41、me dark coloured wires. The contrast formula in 4.4 is limited in its application to white and light coloured wires. Care must be 4.3.2 Picture definition The image of the markings and the wire or cable surface shall be adjusted to ensure that it is sharp and in focus. However, care should be taken
42、NOT to make such adjustments unnecessarily, as this may then require the equipment to be recalibrated. Refer to the manufacturers instructions. 4.3.3 Sample area When measuring the contrast of the marks ensure that measurements are made on the marked and unmarked areas about the central axis of the
43、wire, along its length, and just either side, within a band equal to k 20 % of the diameter of the wire or cable (on small gauge wires this may not be possible due to the limited size of the wire). This is to ensure that the most uniform part of the mark is measured so that errors are not introduced
44、 caused by changes in the laser fluence resulting from the curvature of the wire. See Figure 2. 4.3.4 To ensure a statistically meaningful result, a sufficient number of measurements must be made to take into account variations in the measurement process, including any that may result from the opera
45、tor as well as from the wire and the markings. It is important to ensure that a good average value for the overall contrast measurement for the sample is obtained, regardless of the equipment and the means used. Contrast measurements should be made at multiple points from within the selected wire ma
46、rking, over a minimum length of 50 mm. Contrast values should be calculated for a minimum of 3 separate characters within the sample marking and these should be used to produce an average measurement. Characters should be sampled from either end and in the middle of the code or wire marking. See Fig
47、ure 2. Note that there are generally two different approaches to contrast measurement system design: single point measurement systems and area measurement systems. Single point measurement systems require the user to take individual luminance readings manually from the mark and the background and to
48、 manually compute the contrast value. If using a single point measurement system a minimum of 3 measurement points should be taken from each character mark and a further 3 measurements should be taken for the background unmarked insulation at suitable intervals throughout the sample. Area measuremen
49、t systems typically use a digitised image of the wire surface and automatically calculate the contrast value from many hundred data points obtained from the pixels within the image; in such situations a single measurement only is therefore required for each character. Note also that for single point measurement systems, which typically have relatively larger measurement spot sizes, it is preferable to take contrast measurements on large “block” marks, specially printed for the purpose, as shown in Figure 2. Measurements of contrast values should only be determined direc
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