1、i -A * .EIA TEPLOS-7-A 87 M 3234600 0007373 8 M TEPAC PU B L I CAT I ON Line Profile Measurements in Monochrome Cathode Ray Tubes. TEP105-7-A (Replaces TEP105-1) JANUARY 1987 ELECTRONIC INDUSTRIES ASSOCIATION ENGINEERING DEPARTMENT - EIA TEP105-7-A 87 3234b00 0007374 T NOTICE EIA Engineering Standar
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5、does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Recom- mended Standard or Publication. Published by c c ELECTRONIC INDUSTRIES ASSOCIATION Engineering Department 2001 Eye Street, N.W. Washington, D.C. 20006 PRICE: $5.00 , Published
6、 in U.S.A. EIA TEP105-7-A 87 3234600 0007375 1 INDUSTRIAL CATHODE RAY TUBE TEST HETHOD 105-7A (This test method replaces test method 105-7 previously published in EIA Publication 105-1). This publication was formulated under the cognizance of the JT-20 Committee on Electro-Optic Devices and approved
7、 by the Tube Engineering Panel Advisory Council (TEPAC). developed for industrial cathode ray tubes. They are intended to be useful in evaluating cathode ray tubes with respect to parameters which are of interest to users of these devices. It is expected that, at an appropriate time, this material w
8、ill be forwarded to the US National Committee (USNC) of the IEC as a proposed revision, in part, of IEC 151-14. The TEP-105 series of publications comprise a set of test methods i 1 EIA TEP105-7-A 87 m 3234600 000737b 3 m TEP 105-7 -A Page 1 LINE PROFILE MEASUREMENTS IN MONOCHROME CATHODE RAY TUBES
9、1.0 SCOPE The purpose of this test is to measure the profile of a line on the face of monochrome cathode ray tube (CRT) in order to estimate the resolution capacity of the CRT. Since the display on a CRT often consists of a series of lines or line segments forming alphanumeric characters or graphics
10、 patterns the line width is an important parameter in the determination of the resolu- tion. For this reason, the test method discussed below measures the horizontal and vertical (and possibly diagonal) profiles of the lines produced by the elec- tron beam or beams. From these profiles, the line wid
11、ths can be determined. Such a test for determining the size of the CRT spot is the first step in any resolution calculation. Note that line profiles can also be determined from measurements of the intensity contours of the CRT spot. This method of determining the line profile is not discussed in thi
12、s document. The line profile of the CRT spot is dependent on a number of factors in addition to the focused electron beam distribution at the screen. Some of these factors are: 1. Electron scattering in the screen and support structure 2. Light scattering due to the granular nature of the phosphor a
13、nd the aluminum backing of the screen 3. Saturation of the phosphor 4. Internal reflections and absorption of light in the faceplate and panels mounted onto the faceplate 5. Optical coatings, etches, etc., on the faceplate or panel e External influences on the resolution of the CRT, including ambien
14、t light, are not discussed in this TEP103-7-A Page 2.0 method. These include the transfer characteristics of the viewing system, in particular, the non-linear response of a human observer. Determination of the resolution of a CRT is a complex problem which is not completely solved at the present tim
15、e. The reader is urged to consult the current literature before making any conclusions about the resolution of the display. I TEST EQUIPMENT 2.1 Power supplies are required to operate the CRT under the specified conditions of voltage, current and regulation. 2.2 Deflection supplies providing linear
16、sweeps in each deflection coil axis are required to generate the scan lines to be measured. The supplies should be capable of producing a single horizontal or vertical line at the scan velocity and repetition rate specified for the CRT. If the CRT is to be used in other than a raster display, the de
17、flection supplies should be capable of generating the scan type used in the final display. 2.3 2.4 2.5 A microscope-analyzer consisting of optics, aperture, detector(s) and the necessary power supplies for the system must be provided. It is recommended that a round or rectangular aperture be used. I
18、f a rectangular aperture is used, the long axis of the rectangle must be exactly parallel to the scan line to avoid significant error in the measurement. The detector system must operate in a linear region over the full range of light intensities involved. Complete units available from Celco, EG&G G
19、amma Scientific, Microvision and Photo Research (or equivalent) may be used if suitable. An oscilloscope, chart recorder, storage oscilloscope or computerized data acquisition system is necessary to display and archive the line profile. The test should be conducted in facilities where ambient light
20、levels can be reduced adequately to prevent interference with the measurements. The background, both elect- ronic noise and any ambient light not specif- i EIA TEPLOS-7-A 87 3234b00 0007378 7 = 3.0 TEP105-7-A Page 3 ically accounted for in the measurement, should be as low as possible. It is recom-
21、mended that this background be less than one percent (1%) of the peak intensity. If the line width at 1% of peak height is desired, the background should be significantly lower than this recommended level. TEST SETUP 3.1 The CRT shall be operated at the conditions specified. They shall include all t
22、ube elec- trode voltages as well as an operating condi- tion based on either drive, current, luminous output or radiant output. Deflection param- eters such as yoke type, raster size, writing speed, retrace blanking interval and repetition rate shall be specified if applicable. Specifications should
23、 realistic- ally represent the conditions of use of the CRT. 3.2 3.3 The microscope-analyzer is adjusted so that the image of the scan line is focused on the plane containing the aperture. It is recom- mended that the characteristic dimension of 0.1) of the width of the projected scan line image in
24、the aperture plane measured at 50% of the peak intensity. If this condition is not met, it may be necessary to correct the measured profile for the finite aperture size. The optical system should be such that all the light passing through the aperture is collected by the detector. the aperture be a
25、maximum of one tenth ( On highlight output tubes onemust be care- ful to operate the detector in a linear response mode. This may be accomplished through the use of neutral density filters or a variable aperture objective lens. The diffraction limit of the lens must not be exceeded when using small
26、apertures in the objective lens. It is important that the optical aberrations in the microscope do not appreciably affect the image. The depth of field of the microscope should be considered in evaluating the data. Line profile measurements are generally per- formed at the center of the tube face. I
27、t EIA TEP105-7-A 87 = 3234600 0007379 9 = TEP 105-7 -A Page 4 may be desirable to perform the measurements at the edges, corners or other locations on the CRT face. In these cases, it is important to ensure that the line profile is measured in a direction perpendicular to the scan line. At all point
28、s on the tube face, the aperture plane should be perpendicular to the axis of the tube parallel to the neck. 3.4 Profiles of vertical lines should be taken to measure the horizontal dimensions of the CRT spot. These lines should be produced by driving the vertical coil of the yoke in a manner to pro
29、vide the proper scan velocity and repetition rate. This technique elim- inates the effects of the finite width of the drive pulse and of the finite bandwidth of the video amplifier. In some special cases, it may be possible to make a valid measurement by rotating the deflection yoke by 90 degrees. 4
30、.0 TEST PROCEDURE 4.la The line profile is measured by slowly moving the image of a single scan line (generated by a single gun in a mutiple gun CRT) across the aperture in the direction perpendicular to the scan direction. This motion can be pro- vided by an electrical signal supplied to a deflecti
31、on coil for the axis perpendicular to the scan line, either by the main deflection coil for this perpendicular direction or a separate special purpose coil, or by mechanical motion of the aperture. The cali- bration of the mechanical sweep is easily determined by measuring the total displace- ment o
32、f the aperture. Calibration of the slow electrical sweep can be achieved in many ways. Several possibilities are: 1) The scan line can be deflected a large distance which can be measured with either a ruler or a special gauge. 2) A second aperture in the image plane will give two line profiles separ
33、ated by a known distance. 3) A large external mask containing two comparatively large slits a known distance apart can be used to determine the relation- ship between distance and deflection current. t EIA TEPLOS-7-A 87 m 323Yb00 0007380 5 m 5.0 TEP105-7-A Page 5 4) The gain of the deflection amplif
34、ier may be changed by a known factor and the larger of the deflection amplitudes measured. A time averaging detector/amplifier or a peak detector with cample and hold electronics should be used to eliminate the effects of the phosphor decay and the periodic nature of the signal. 4. lb The line profi
35、le may be measured using a photodiode array scanner. In this instru- ment, a microscope is used to focus the image of the scan line on a linear photodiode array. The array should be perpendicular to the scan line and the microscope focused carefully to obtain accurate line widths. Both of these cond
36、itions can be obtained by adjusting the microscope focus and orien- tation for minimum width of the scan line. Calibration of the instrument is uniquely determined by the photodiode array spacing and the magnification of the microscope. A frequent source of problems is the zero beating effect, resul
37、ting from heterodyning of the display rates with the diode array scan rate. This can be cured by either syn- chronizing the display and the photodiode scan rates or by a long integration time for the photodiode array. The photodiode array generates a sampled profile of the scan line. Some diode arra
38、ys have a dead space between the actual pixels in the array and theremay be pattern noise due to variations in response of the individual diodes in the array. Also individual pixels may vary in sensitivity by as much as 20%. 4.2 The line profile is plotted or otherwise stored for further processing.
39、 DATA 5.1 A minimum set of data shall consist of hori- zontal and vertical line widths at 50% and 5% of the peak intensity of the beam of the CRT measured at the center of the screen. Measurements at the 1% level are particularly useful for comparisons of gun designs and for evaluation of the percep
40、tual. charac teric tics _. EIA TEPL05-7-A 7 3234b00 0007383 7 H TEP105-7-A Page 6 6.0 5.2 of the resulting display. Plots of the measured line profiles may be supplied and modulation transfer functions (MTF) or just noticable difference (JND) analyses may be perf ormed. PRECAUTIONS It is recommended
41、 that the line widths be reported as a function of focus voltage over the nominal focus range of the CRT. The criteria used to determine the optimum focus must be carefully specified. In addition, line width measurements at other than the center of the screen allow better evaluation of the quality a
42、nd suitability of the CRT. 6.1 Care must be taken not to saturate the detector system such that its response becomes nonlinear. 6.2 Optical focusing of the scan line image onto the aperture plane is critical. Visual focus is operator dependent and may not correspond to optimum photometric focus. A u
43、seful method of optimizing the photometric focus is to maximize the detector signal when the image of the maximum intensity portion of the scan line is directly over the aperture. 6.3 6.4 Measurements taken at locations other than the center of the tube are dependent on the deflection yoke, beam sha
44、ping coils, and geometry correction used. Care is required in deflection yoke selection to isolate the CRT characteristics from those of the yoke. Even with uniform field yokes, the spot shape may be dependent on the length of the yoke field. Although not specified in this document, the following it
45、ems should be considered as they affect the accuracy and repeatability of the measurements: 1) Power supply stabiliky and accuracy 2) Deflection and video jitter 3) Mechanical stability of the apparatus 4) Static and dynamic electromagnetic fields in the area of the CRT, including those EIA TEP105-7
46、-A 87 W 3234600 0007382 9 W t 6.5 TEP105-7-A Page 7 intentionally used for geometry correction. When using either a round aperture or a linear diode array, errors of up to 20% may occur due to variations in phosphor grain size along the scanned line. Measuring several posit-ions on the scanned line may be a way to average the phosphor effects. Using a scanning slit eliminates this error by averaging the linewidths along the slit.
