Automatic Degaussing of Display panels by Analysing Signal Generator and Gauss Controller

Transcription

1 International Journal of Electronics Engineering, 4 (1), 2012, pp Serials Publications, ISSN : Automatic Degaussing of Display panels by Analysing Signal Generator and Gauss Controller Sarika Malhotra 1, Sayed A. Imam 2 & R. K Singh 3 1 Member IEEE Associate Professor, RKGIT, Gaziabad, U.P., India 2 Member IEEE, Jamia Milia Islamia Universit., Delhi, India 3 Professor, ECE Deptt., Kumaon Engineering College, Dwarahat, India ( sarika_jatin@yahoo.com) Abstract: The characteristic of the display panels depends on the purity adjustment as well as on its resolution and on the magnetic field of Earth. The magnetic field of the Earth varies from one region to the other. The variation the Earth s magnetic field introduces colour patches in the display devices if the adjustment of the display panel is not performed as per the regional Earth s magnetic field. The adjustment process to adjust the display characteristic as per the Earth s magnetic field is carried out by Gauss adjustment process. In this paper we present an approach for the automatic gauss adjustment process by using a gauss controller and a pattern generator having the capability to produce Red, Green, Blue signals, known as Purity patterns. Keywords: Gauss level, Pattern Generator, GPIB Degaussing, RGB Generator, Colour Purity. 1. INTRODUCTION The colour purity of the display panel is highly affected by the Earth magnetic field. The magnetic field of Earth varies from one region to the other. The manufacturing facilities of the display panels are not available in all regions w.r.t. the Earth magnetic field chart/values. The characteristics of the display panels are adjusted with respect of the region in which it is going to be used. This is the reason for the problem observed in the display panels, such as colour patch on the screen when a display panel is used in region for which it is not manufactured. The display panels used in televisions, medical monitors, computers, cameras other interactive devices are highly sensitive to the surrounding magnetic field. The magnetic field is not only Earth s magnetic field, but also stray magnetic effects from a strong permanent magnet or from a power source or from Electro magnets. The colour Tint, Hue and purity levels are very sensitive to the surrounding magnetic field. During manufacturing of the display panels, the adjustment of the panels is due by considering all the factors that may contribute towards the total disturbance in the magnetic environment surrounding the display panel. 2. MAGNETIC FIELD A magnetic field can be represented by lines of induction or flux lines. These lines are invisible and are produced by magnetized material or by electrical currents. Magnetic fields are electrical in nature, and the magnetic field caused by a long straight line of current is simulated in Figure 1. The flux lines are continuous and exist in closed loops. A unit of magnetic flux is called a Maxwell (a line). The magnetic flux density (B) at any point is defined as the number of lines passing through an area, which is perpendicular to the direction of the flux lines. The magnetic flux density (B) is called a gauss (the number of lines per square centimeter), which is a vector quantity (a magnitude and direction at any point). The unit of flux density (B) is the gauss. Figure 1: Magnetic Field Around Straight Conductor 2.1. Earth Magnetic Field Earth behaves like a huge magnet with two poles namely South Pole and North Pole. The Effects of these poles is seen all over the earth. The intensity of the magnetic field varies form one location to the other. As per the pattern of magnetic characteristics of the earth, the total Earth s surface

2 34 International Journal of Electronics Engineering is divided into different regions. In one region the magnetic field virtually remains constant. The average magnetic field of one region is calculated and is used to adjust the characteristic of the display panel accordingly. The magnetic field of the earth has Three components: (i) Vertical Component called Bv (ii) Horizontal Component called Bh (iii) Axial component called Zx Figure 2: Earth Magnetic Field lines The magnitude of the magnetic field is known as Resultant magnetic field and is calculated after analysing the overall effect of the three components of the Earth s magnetic field. The display panels are adjusted by considering the resultant magnitude of the earth s magnetic field. (i) Stray Magnetic Fields: These magnetic fields are the magnetic circles present in the close vicinity of the display devices, which may result from the influence of a strong magnetic field producing substance. (ii) Magnetic Fields by Devices: These magnetic fields are produced by instrument or devices in which highly inductive components are present. High voltage cables and transformers are also responsible for such kind of magnetic interference. (iii) Magnetic Field Due to Permanent Magnets: If the display devices are placed close to the permanent magnets, the display properties are adversely affected. The permanent magnets create a strong magnetic field, which alters the characteristic of the display panel. (iv) Electromagnet Magnetic Field: The electromagnets are generally used in various appliances and the magnet comes into action only after certain circuitry is operated. Such kind of magnetic fields are difficult to detect as it becomes active only for the duration, for which the Electro magnet is being operated Effects of Magnetic Misalignment The magnetic misalignment of the display panel results into various serious after effects which can make the display panel unfit for Use. Following are the main after effects of the misalignment: (i) Colour Patch Problem: The colour patch problem in the display panel is due to presence of a patch of particular colour on the other colour as explained in the following Figure: Figure 3: World s Earth Magnetic Chart 2.2. Other Magnetic Fields The presence of magnetic fields other than Earth s magnetic field also affects the display qualities of the display panel. The presence of other magnetic fields can be due to following factors. Figure 4: Colour Patch The colour patch can be of any colour and the shape of the patch may also vary, depending upon the intensity as well as the effect of the magnetic field.

3 Automatic Degaussing of Display Panels by Analysing Signal Generator and Gauss Controller 35 operator and the adjustment of the display panel is done by considering the purity status of the panel. Figure 5: Colour Patch on Test Pattern The presence of colour patch on test pattern does not allow the operators in the manufacturing line to make judgement about the alignment of the display panel. (ii) False Colour: The display panels has versatile use. Sometime the decision is based on the colour of certain component on the display panel. The magnetic misalignment can alter the colour of a particular portion, which can result into false alarm. Figure 6: False Colour In the Figure 4, the red line is overshadowed by a false colour. The decisions based on the presence or absence of Red line cannot be taken as the presence of line is in doubt. (iii) High Rejection Ratio: The display panels which are not aligned as per the magnetic field, also fails in other attributes of the quality testing, such as Resolution Test, Contrast test and other parametric measurements. As a result, the overall rejection ratio of the panel increases Manual Degaussing Process The manual degaussing process corresponds to the degaussing process in which the procedure is carried out by the operator with the help of certain instrument. In this process the purity of the display device is judged by the Figure 7: Manual Degaussing Process 3. LIMITATIONS OF MANUAL DEGAUSSING PROCESS (i) Human Error: This process is totally based on the judgment of the operator. The purity of the display panel is judged by the human eye and the colour patches are removed by using a manual Degaussing Coil. As a result the purity of the one display panel varies from another. (ii) Exposure to X-rays: To perform the degaussing process manually, the operator has to stand near to the display panel. In case of CRT based display panel, X-rays may escape from the panel, which adversely effects the health of the operator. (iii) Analog values based process: The manual process is an analog process, log files can not be created, which results into a non quality tracking process. The other disadvantages include, more tack time, lower productivity, non linearity of the process, which makes it unfriendly for use. 4. AUTO DEGAUSSING PROCESS The Auto degaussing process presents an approach for the automatic degaussing of the display panels by using interactive instrument which has the capability to be controlled by a GPIB port (general purpose interface bus). The induction of degaussing process introduces high quality linearity in the adjustment of the display panels. More over the data can be fed in a digital mode and can be changed with respect to the place where the final product (display panel) is to be used. Main components of the automatic degaussing process are: (i) Gauss Chamber (ii) Automatic Gauss Parameter Controller (iii) GPIB Pattern Generator (iv) Automatic Degaussing coil (v) Status Display Monitor (vi) DC power supplies. The following Flow Diagram explains the process of Automatic Degaussing of the display panel:

4 36 International Journal of Electronics Engineering vertical and axial component of the magnetic field produces by the Gauss chamber. The gauss chamber produces a DC magnetic field, generated with the help of certain coils in which Dc current flows. The change in the value of DC power supplies which feeds the DC voltage and current to the coils of the Gauss chamber, changes the overall values of the magnetic components. This creates a virtual magnetic environment of the place to where the display panel is to be used. The values of magnetic field generated by the chambers are typically in milli gauss which is safe for humans and the surrounding working areas Performing Automatic Degaussing (i) Step 1: The display panel is placed in the Gauss chamber and the desired Earth s magnetic Field conditions are simulated with help of automatic degaussing controller by altering the values of the connected DC power supplies. (ii) Step 2: The display panel is connected to the RGB generator. The RGB generator corresponds to a video signal generator, which has the capability to generate RED, Green, Blue patterns in the designated video format. (iii) Step 3: For parametric measurement the RGB generator is connected to the PC as well as to the display device trough GPIB port. The values of the signal supplied to the display devices can be altered from the PC itself. In this way a virtual display conditions as per the predefined use of the display panel can be simulated. (iv) Step 4: The purity of the display panel is analysed. If any colour patch is seen on the panel, it is removed by the automatic degaussing coil. (v) Step 5: The Purity of the display panel is checked. The digital values are stored in PC by creating a Log File. If the display panel shows any deviation from the desired characteristic, the whole process is repeated. Figure 8: Flow Chart The auto degaussing process utilises a gauss chamber. The Gauss chamber has the ability to generate the Gauss values as per the Earth s magnetic field. The components of the Earth magnetic field in the different region of the earth can be simulated with the help of automatic degaussing controller. The automatic controller varies the horizontal, Figure 9: Block Diagram of Automatic Degaussing Process

5 Automatic Degaussing of Display Panels by Analysing Signal Generator and Gauss Controller 37 The above figure explains the automatic degaussing process of the display panel. After the completion of process, the display panel is checked for its purity in colour and the log file generated during the process is stored for quality tracking. 5. CONCLUSION The Automatic Degaussing of display panels is being carried out by analysing and correcting signal waveforms generated by the signal Generator.This system makes the overall process very accurate and it empowers the testing to be carried out in the virtual test environment, irrespective of the actual test site. The colour purity of all the display panels produced is comparative and similar. It reduces the overall tack time of the process and reduces the dependencies on human judgment. REFERENCES [1] De hann, T. G. Larragy, M.M. ojo, R. J. Philips Semocond, Eindhoven, Television Noise Reduction IC, IEEE Preceeding, Vol 44, Issue 1, pp , Feb [2] A. Punchihewa, D. G. Bailey and R. M. Hodgson, Objective Quality Assessment of Coded Images: The Development of New Quality Metrics, Proceedings of Internet, Telecommunication Conference, Adelaide, Australia, pp. 1-6, [3] Tetsui Ryoichi, Signal Generator of Digital TV Generation LCD, Semicond FPD Word Proceeding, Vol. 23, pp , [4] Mehmet Engin, Rasim Saltuk Alakus, Elimination of White Noise from Video Signals of Television Transmission by Using Digital Recursive Method, Istanbul University, Journal Electrical & Electronics, pp , June [5] B. Grob, C. E. Herndon, Basic Television and Video Systems, 6th Edition, McGraw-Hill, Singapore, pp. 292, [6] Dr. Saupe & Dr. Xiong Book on, Efficient Error Protection for Image and Video Transmission Over Noisy Channels, Univ. Konstanz & Univ A&M Texas Precceding May [7] M. Robin and M. Poulin, Digital Television Fundamentals, McGraw Hill, New York, USA, Second Edition, p. 126, [8] Tanaka Y, Video Signal Noise Characteristics with Regard to Scanning Method, IEEE Preceeding, Vol. 40 Issue 2, pp , Aug [9] Van Roermund, Snijder R. J. Philips Res. Lab A General Purpose Programmable Video Signal Processor, IEEE Proc. Vol. 35, Issue 3, pp , August [10] A Peiravi & S Toosizadeh, Automatic Adjustment of Television Sets Using an Unacalibrated Camera with a Novel Fuzzy Test Pattern and an Adaptive Algorithm, Journal of Applied Sciences, Ferdowsi Univ, Mashhad, Iran Asian Network for scientific Information, Vol. 9(1), pp , [11] Frederick, C. Everett, Recoginition and Coreection of Waveform Errors in TV Transmission, IEEE Trans on Boradcastings, Vol. BC-18, No. 1, pp. 18 to 22, March [12] Tsuyoshi Harada, Yoshie Oritake on Video Signal Defect Compensation System, US Patent No , US Classification, 358/8; 360/38, Feb [13] J Carl Hooper, Dr. Sunnyvale, Sydney, Noise Reduction System for Video Signals, US Patent No. pp. 1 to 15, Feb [14] A. Punchihewa and D. G. Bailey, Artefacts in Image and Video Systems; Classification and Mitigation, Proceedings of the Conference of Image and Vision Computing New Zealand, Auckland, New Zealand, pp , [15] A. Punchihewa, D. G. Bailey and R. M. Hodgson, A Survey of Coded Image and Video Quality Assessment, Proceedings of Image and Vision Computing New Zealand, Palmerston North, New Zealand, pp , This work was supported in part by the Raj Kumar Goel Institute of Technology, Ghaziabad (Uttar Pradesh) and Jamia Millia Islamia University New Delhi.