1、Q W I- a TEPAC PU B L I CAT I ON Measurement of Phosphor Persistence of CRT Screens TEP105-14 ELECTRONIC INDUSTRIES ASSOCIATION ENGINEERING DEPARTMENT - EIA TEP105-14 87 = 3234600 0007340 4 L * NOTICE EIA Engineering Standards and Publications are designed to serve the public interest through elimin
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5、bligation whatever to parties adopting the Recom- mended Standard or Publication. Published by ELECTRONIC INDUSTRIES ASSOCIATION Engineering Department 2001 Eye Street, N.W. Washington, D.C. 20006 PRICE: $8.00 Published in U.S.A. - EIA TEPLOS-14 7 M 3234600 000734E b = TEP1 O 5 - 14 MEASWEbJl“- OF P
6、HOSPHOR PERSISTENCE OF CRT SCREENS This publication was formulated under the cognizance of the JT-31 Committee on Optical Characteristics of Display Devices and approved by the Tube Engineering Panel Advisory Council (TEPAC). The TEP105 series of publications comprises a set of test methods develope
7、d for industrial cathode ray tubes. cathode ray tubes with respect to parameters, which are of interest to users of these devices. They are intended to be useful in evaluating i .- I - EIA TEP105-14 87 3234b00 0007342 8 W TEP10 5-14 I MEASUREMEW OF PHCSPHCR PERSISTENCE OF CRT SCREENS TABLE OF cX“TS
8、Paragraph I. SCOPE II. EQUIPMENT III. OPERATING CONDITIONS IV. METHODS OF V. PRESENTATION OF DATA FIGURE I - PERSISTENCE MEASURING EQUIPMENT ADDFNDUM I ADDENDUM II Page 1 1 *3 5 7 9 10 12 ii EIA TEP105-14 87 3234600 O007343 T - TEP105-14 Page 1 MEASUREMENT OF PHOSPHOR PERSISTENCE OF CRT SCREENS I. S
9、cope This specification will outline test methods suitable for measuring persistence of CRT screens. This data will be used primarily for registration of phosphors in the WTDS system. used as a general guideline to the suitability of e phosphor to a particular application. persistence and perceived
10、flicker is very poorly understood., published persistence data alone will not be sufficient to determine if a phosphor meets ergonomic criteria. the suitability O a phosphor is by direct experiment under identical conditions the end user will encounter. This data may also be Since the relationship b
11、etween measured Normally, the only way to determine II. Equipment The basic equipment problem related to the measurement of persistence is insuring the frequency response of all equipment used is high enough. that will be used for human viewing. flying spot scanner phosphors, may require even higher
12、 frequency response. necessary to measure persistence of phosphors. Normally, 10 MHZ response is fast enough to test all phosphors Speciaiized applications, such as Figure I is a diagram of the various pieces of equipment 1. HV Supply, Focus Supply, Scanner and Yoke This equipment should be suitable
13、 to drive the tube under test. special frequency response requirements are imposed on this equipment. spot method, although they make it easier to set the proper pulse conditions. 2. Pulse Generator No The scanner and yoke are not required for the pulsed The pulsed spot persistence method (see Secti
14、on IV) is the most demanding of the pulse generator. To use this method, the pulse generator must be able to pulse the tube on with rise and fall times of 50 nS and pulse widths of .l - 1 pS. In order to pulse the tube properly, the generator must normally pro.duce 5OV pulses into the CRT load. EIA
15、TEPLOS-111 7 3234b00 0007344 L TEP105-14 Page 2 II. Equipment (contd.) 3. Photodetector and Amplifier Traditionally, photomultipliers with S-20 type response have been used as a photodetector. diodes have shown the high speed devices are fully satisfactory and, in some apsects, superior to PMTs. In
16、any event, the photodetector must be eye-corrected so it matches the CIE Y curveo Serious and unrecognized errors have resulted in the past when non eye-corrected photodetectors have been used to measure persis- tence. Normally, fast phosphors that require the full 10 MHZ of detector frequency respo
17、nse have relatively high peak light output, and photodetector sensitivity is not a serious problem. photomultiplier is used, a relatively small load resistor, often as little as 100 ohms, will convert the photocurrent into a usable voltage. Slow phosphors, on the otherhand, normally have a low peak
18、light output and PMT sensitivity is increased by increasing the load resistance. that the speed of the photodetector is at ali times at least 10 times faster than the decay of the phosphor to be measured. Recent experiments with silicon photo- If a The person measuring persistence must insure If an
19、external amplifier is used, as is frequently the case with a solid state photodetector, this unit must also have at least a 10 MBZ bandwidth. Since a silicon photocell in the photo voltaic mode is non-linear unless it operates into very low load resistance, the amplifier must be a current to voltage
20、 converter, rather than a simple voltage anplifier. the photocell in the photo conductive mode with a reverse bias, typically 20-1OOV. way a load resistor is used on a Ptn. This problem can be overcome by using Then a load resistor may be used, in the same Another approach to the photodetector speed
21、 problem is to purchase an integrated/photodetector amplifier combination where the manufacturer has built in the required speed and sensitivity. 4. Data Display and Recording A convenient way to display and record persistence curves i-s on a high speed digital oscilloscope, waveform recorder or osc
22、illoscope plug-in to a personal computer. A system must have a digitization EIA TEPL05-14 87 = 3234600 0007345 3 = TEP105 - 14 Page 3 II. Equipment (contd.) 4. Data Display and Recording (contd.) rate of 5 MHZ (either real or equivalent time) to be generally useful for CXC work. operator to set the
23、system up quickly, and the digital output of the systen facilitares further processing of the data. The display unit of the system allows the Other systems that have been used to record data in the past that are still useful when used with czre are the use of an analogue storage oscilloscope, a box
24、car integrator, or a non-storage oscilloscope in conjuction with an oscilloscope camera. A non- storage oscilloscope used without a camera is not recommended for the pulsed raster method and must be used with extreme care in the pulsed spot and pulsed line methods. Use of a personal computer sbiplif
25、ies data znalysis , especially computing the integrated light remaining cume and the ripple ratios of a phocphor (see SectionV). Data may be entered into the computer three ways: 5. a. Direct transfer from a digital oscilloscope or waveform recorder b. Direct transfer from a digitizer after digitizi
26、ng photographs or analogue recorder outputs. C. Through the keyboard after manual digitization. III. Operating Conditions The aper-ating conditions described in this section shall be used for measuring the persistence of phosphors to be registered with the Electronic Indristries Associztion under TE
27、PAC PUBLICATION No. 116. Other operating couditions nay of course be used when it is known that the final application of the phosphor screen will differ from those described here . An anode voltage of 15KV and anode current of 100 pi (full raster) shall be usedunless some other value is appropriate
28、for a particular tube and phosphor. Cathode ray tubes 02 the bipotential lens type should be used as the beam current reaching the phosphor screen can be directly and accurately measured. the final anode power supply minus leakage current measured with the tube under test in a biased “off“ condition
29、. This current is equal to the current supplied by EIA TEPLOS-14 7 = 323YbOO 00073Yb 5 TEP10 5 - 14 Page 4 III. Operating Conditions (contd.) Alternatively, tubes of the einzel lens type may be used if the electron beam is not trimmed by apertures connected to the final anode power supply. Ail other
30、 voltage requirements for the tube under test should be supplied according to the typical operating conditions for the type of tube being used. The anode current can be measured by placing a battery powered digital volt meter with a current shunt in a clear plexiglass box and allowing the meter to f
31、loat up to the anode voltage. IV. Methods of Measurement Three methods are described in this specification: pulsed spot, pulsed line and pulsed raster. The chart below indicates which method should be used according to the classification of the phosphor in TEPAC PUBLI- CATION No. 116. If the classif
32、ication is not known as with an un- registered phosphor, it is suggested that the pulsed line method be followed until the classification is determined. O The reason for having three methods is one of measuring ease. Phosphors with long decays are difficult to measure using the pulsed spot method du
33、e to low light levels. Fast phosphors cannot be measured by the pulsed raster method due to interference from adjacent raster lines . Tine to Rise to 90% Word Description or to Decay to 10% of Luminescence Rise Persistence Peak Brightness Time or Decay Measurement Method 1 sec. or over Very Long Pul
34、sed Ras ter 100 msec. - 1 sec. Long Pulsed Raster 1 msec. - 100 msec. Medium Pulsed Line or Pulsed Raster 10 usec. - i msec. Medium Short Pulsed Line or Pulsed Spot 1 usec. - 10 sec. Short Pulsed Spot less than 1 usec. Very Short Pulsed Spot For each method, it is recommended that two final anode or
35、 beam currents are used so that two curves may be plotted. This may show the tendency of the phosphor to change its persistence characteristics with a change of brightness. A. Pulsed Spot Method 1. Apply all voltages as required to the tube under test (TUT). 2. Apply scanning to the tube so that a r
36、aster appears on the phosphor screen. EIA TEPLOS-14 87 m 3234b00 0007347 7 m TEPlO5-14 Page 5 IV. Methods of Measurement (contd.) O A. Pulsed Spot Method (contd.) O 3. 4. 5. 6. 7. 8. 94 10. Set the drive level, usually by varying the Gl voltage, until an anode current of 100 or other selected value
37、is obtained. Record the G1 voltage. Set the pulse generator so it drives the G1 to the voltage recorded in step 3 when the pulse is “ON“ and drives the tube to cutoff when the pulse is off. The pulse width should be set to a value corresponding to the approximate dwell time of the electron beam on t
38、he phosphor. For phosphor registration purposes, 0.5 pS should be used. If the light level is insufficient, the pulsed spot method is inappropriate and the pulsed line or pulsed raster should be used The pulse repetition frequency (PRF) should be set to 60 2 (16.6 mS) or some other appropriate value
39、. pulses should be at least twice the expected time for the phosphor to decay to 1%. The time between At this point, with the raster on, pulses should appear at random locations on the screen. When the raster is turned off, the pulse will stabilize in the center and appear to be on continuously, sin
40、ce 60 HZ is above the critical fusion frequency for virtually all observers. Place the photodetector so the maximum amount of light gets into it. detector in contact with the tube, centered over the spot. This normally means placing the front surface of the Check the photodetector for saturation by
41、placing a 0.3 neutral density filter in front of the detector. The signal should be reduced 50%. If the signal is reduced by less than 50%, or if the curve shape changes, reduce the light to the photodetector with a neutral density filter or by moving the detector back and repeat this test. Record t
42、he decay curve to the 1% level using the equipment in Section 1-4. If practical, record the data to the 0.1% level. B. Pulsed Line Method The pulsed line method provides considerably more light to the photodetector than the pulsed spot method. This method is not appropriate if the expected decay tim
43、e to 10% is less than about 100 us. EIA TEPLOS-14 87 m 3234600 0007348 9 TEP105-14 Page 6 IV. Methods of Measurement (contd.) B. Pulsed Line Method (contd.) 1. Follow steps 1 - 4 Por the pulsed spot method. 2. Set the pulse width to 32 pS. the horizontal sync signal, Trigger the pulse generator on S
44、et the PRF to 60 HZ or slower. 3. Collapse the vertical raster until only a line remains. Reduce the horizontal raster unci1 the line is 2“ long. If step 2 was not followed correctly, this may bum the tube. 4, Set the photodetector to see the center portion of the line. 5. 6. Record the decay curve
45、of ehe phosphor to the 1% or 0.1% level. Check the photodetector for saturation. C. Pulsed Raster Method This method provides more light to the photodetector than the pulsed line. It is not appropriate if tlie expected decay time to 101: is less than about 19 mS. 1. Follow steps 1-3 in the pulsed sp
46、ot method. 2. The pulsed raster method can be either a single shot or periodic. For single shot operation, allow the raster to stab- ilize and pulse the tube “off“ during the vertical retrace. For periodic operation, pulse the tube “on“ long enough to stabilize and “off“ until the phosphor: decays t
47、o 1% or 0.1%. The on and off times should be equal arid are typically 0.25 - 1 second. (See addendum) Set the photodetector to see the center portioa of the raster. 3. 4. 5. Check the photodetector for saturation. Record the decay curve to the 12 or 0.1% level. D. Notes S,C=O FOR Ta0 TO Ti a. D=D*VC
48、T) S-S+VCT)nSINCP2nT) C*C +VCf)eCOS CP2xt3 NEXT T _. R=SQRCCnC+SSS)/ PRINT USING 1770 5 F.R NEXT I Ripple ratio! PRINT o PRINT e PRIHT e PIIHT TEPlO5-14 Page 11 TEP105- 14 Page 12 ADDENDUM II EIA TEPLOS-14 87 3234600 0007354 4 . Alternate Pulsed Raster Method The note in section IV.D.2 refers to a p
49、ossible effect of excitation mode and duration upon the duration of the phosphor persistence signal. The field of view of the photodetector is cited as a factor in this interaction. This addendum illustrates a useful application of increasinq the field of view of the photodetector while measuring the persistence of a pulsed raster. I. Move the detector at least a raster dimension away from the phosphor screen, so that it views the entire raster. 2. Excite the raster with a pulse longer than 33 milliseconds, or simply bias on the beam without applying a periodic pulse. 3.
