ECA TEP197-A-1997 Preparation of X-Radiation Characteristic Curves for Cathode Ray Tubes《阴极射线管X射线特征曲线制备》.pdf

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1、 STD-EIA TEPL97-A-ENGL L997 = 3234b00 05bL37 583 TEPAC PUBLICATION Preparation of X-radiation Characteristic Curves for Cathode Ray Tubes TEPl97-A OCTOBER 1997 ELECTRONIC INDUSTRIES ASSOCIATION ENGINEERING DEPARTMENT STD EIA TEPL77-A-ENGL 3234hOO 058bL40 2T5 . NOTICE EIA Engineering Standards and Pu

2、blications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchasers in selecting and obtaining with minimum delay the proper product for their partic

3、ular needs. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of EL4 from manufacturing or selling products not conforming to such Standards and Publications, nor shali the existence of such Standards and Publications preclude their voluntary use

4、by those other than EL4 members, whether the standard is to be used either domestically or internationally. Standards and Publications are adopted by EIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, EL4 does not assume any liability to any patent

5、 owner, nor does it assume any obligation whatever to parties adopting the Standard or Publication. Technical Publications are distinguished from EIA Standards or Interim standards in that they contain a compilation of engineering data or information useful to the technical community and represent a

6、pproaches to good engineering practices that are suggested by the formulating committee. This Publication is not intended to preclude or discourage other approaches that similarly represent good engineering practice, or that may be acceptable to, or have been accepted by, appropriate bodies. Parties

7、 who wish to bring other approaches to the attention of the formulating committee to be considered for inclusion in future revisions of this publication are encouraged to do so. It is the intention of the formulating committee to revise and update this publication from time to time as may be occasio

8、ned by changes in technology, industry practice, or government regulations, or for other appropriate reasons. prom Roject No. 3979, formulated under the cognizance of the JT-32 Electron Tube Safety Committee.) Published by ELECTRONIC INDUSTRIES ASSOCIAON 1997 Engineering Department 2500 Wilson Boule

9、vard Arlington, VA 22201 PRTCE: Please refer to the current Catalog of EIA, JEDEC, and TIA STANDARDS and ENGINEERING PUBLICATIONS or call Global Engineering Documents, USA and Canada (1-800-854-7179) International (303-397-7956) All rights reserved Pnnted in U.S.A. STD-EIA TEPL77-A-ENGL 1777 - 3234b

10、00 058bL4L L3L c Preparation of X-radiation Characteristic Curves for Cathode Ray Tubes CONTENTS Page I Foreword 111 1 Introduction 1 2 Adjustment of X-radiation data 1 2.1 Normalization to a different beam current 2 2.2 Calculation of X-radiation at minimum glass thickness and minimum absorption co

11、efficient 2.3 Data acquisition 4 3 Construction of X-radiation characteristic cuves 7 3.1 Color - entire tube 7 3.2 Color - tube anode contact 9 3.3 Monochrome - cathode ray tubes 14 4 References 16 Foreword STD.EIA TEPL7-A-ENGL 1997 3234b00 05bL42 078 I This standard was prepared by the Electronic

12、industries Associations JT-32 Electronic Tube Safety Committee Task Force on X-ray Measurements. iii Previous page is blank TEP 197-A Page 1 1 Introduction In accordance with the Radiation Control for the Health and Safety Act of 1968, cathode ray tube (CRT) manufacturers are required to submit an i

13、nitial report to the Center for Devices and Radiological Health (CDRH), an agency of the U.S. Department of Health and Human Services (DHHS). The initial report for cathode ray tubes must provide results of the testing and measuring of the X-radiation emissions from a cathode ray tube. The initial r

14、eport for a new CRT tube is submitted by a manufacturer. The parts of the initial report to be discussed by this document are the preparation of the data plots for X-radiation limit curves and 36 pAikg isoexposure-rate limit curves. The X-radiation limit cuwe defines the relationship between CRT hig

15、h- voltage and the X-radiation exposure rate (pNkg) under a constant beam current. The “36 pNkg isoexposure rate limit curve“ defines the combinations of CRT anode voltages and beam currents that produce a constant rate, in this case 36 pAikg, of X-radiation emission from the CRT. Usually, such limi

16、t curves represent the worst case conditions for X-radiation emission from the CRT. Pertinent parameters to be reported are the registration reference points and limit curve slope factors. Throughout this document the terms CRT high-voltage“ and “anode voltage“ mean the overall acceleration of the e

17、lectron beam from cathode to final anode. Two limit curves should be developed, one for the entire CRT and one for the anode contact. The following instruction for the preparation of the X-radiation characteristic curves is recommended to insure uniformity throughout the CRT industry. NOTE-TO confor

18、m with the International System of Units (SI) dimensions, the unit for radiation exposure of pA4g“ (picoamperes per kilogram) has replaced “mWh“. The SI equivalent of 0.5 mWh is 36 pikg. The relationship between the two measurements scales is: 1 mWh = 72 pNkg 2 Adjustment of X-radiation data In the

19、development of X-ray limit curves, five adjustments are made to the original data. All of these changes could, in principle, be accomplished “physically“; that is, by actually measuring tubes that were constructed of minimum specified glassware and tested at the standard reference beam current. Howe

20、ver, the practicality of such testing is beyond tube manufacturing and radiation detection methods of accomplishment. Adjustment of the X-radiation data to glass of minimum thickness and minimum absorption coefficient, with additional safety margin, is a five step process. Step 1) Step 2) Step 3) St

21、ep 4) Step 5) Adjust exposure rate data for background, meter calibration factor, etc. detection system operations manual. Refer to The test beam current is normalized to the standard reference current (see 2.3.5) specified for the tube being tested. See 2.1. Convert the data from step 2 to the expo

22、sure rate expected from a tube constructed with materials that are of minimum specifications for glass and glass absorption. See 2.3.6. thickness Calculate the sample average (x), sample standard deviation (o), and (% + 30 ) for the converted data from the previous step. See 2.3.7. Establish a guard

23、band for the results from step 4. See 3.1.5. TEP 197-A Page 2 It may be instructional at this time to review the consequences of making the various adjustments to the measured X-ray data. To this end a hypothetical X-radiation curve was synthesized. 2.1 Normalization to a different beam current Beca

24、use the X-radiation exposure rate is linearly proportional to the beam current, shifting from one beam current level to another is done by simple proportion. The curve is simply translated up or down. In figure 1, the original curve (It, = 300 fi) has been shifted upward by a factor of 10. In practi

25、ce, a 3000 pA curve may be developed first and a 300 pA cuwe would then be derived by dividing by a factor of 10 (see figure 1 I 1000 t 1). M x P, X w 1 O0 36.00 10 v1 v2 v3 v4 VE3 Anode Voltage - kV Figure 1-Adjustment due to different beam current 2.2 Calculation of X-radiation at minimum glass th

26、ickness and minimum absorption coefficient In practice, actual glass thickness and absorption coeficient always exceed minimum. In addition, X- radiation increases with decreased thickness and/or with decreased absorption coefficient. Therefore, adjustments to the measured X-radiation values must be

27、 made to predict worst case emission for glass containing minimum thickness and minimum absorption coefficient. In a composite material such as glass, each component element absorbs independently of the other elements. Hence, the effective mass absorption coefficient for the composite glass (osiass)

28、 is the summation of these separate elemental absorption contributions shown in equation 1. n where fc is the mass fraction of component; a is the mass absorption coefficient of component. TEP 197-A Page 3 The linear absorption coefficient (p) at a specific X-ray wavelength equals the density (p) mu

29、ltiplied by the mass absorption coefficient (u) for that wavelength shown in equation 2. (2) P=Pw Conventional practice is to characterize the X-ray absorption of CRT glassware by the linear absorption coefficient at the wavelength of 60 pm (20.6 kev). CRT glass manufacturers will supply, to the tub

30、e manufacturer, linear absorption coefficient data at 60 prn. The data is representative of the glass produced during the reporting period. The date code applied to the CRT glass components identifies the date of glass manufacture. Because the glass absorption and therefore the half-value layer are

31、voltage dependent, an adjustment must be made to the absorption data supplied to the tube manufacturer. The adjustment will scale the reported linear absorption coefficient specified at 60 pm to other wavelengths. The transformation follows equation 3. 2.75 L J where bff is the effective absorption

32、coefficient; (3) I, is the minimum absorption coefficient at 60 prn; E is the anode voltage in kV When chosen anode voltage. is substituted into the following equation, the result is the half-value layer HVL ( in cm) at the NOTE-Alternatively, HVL may be measured experimentally, if desired. EXAMPLE

33、l-What is the HVL of a glass sample with a specified minimum p of 28.0 cm“ when the tube is operating at E = 33.0 kV? bfi = 28.0 x (l .24/33.0)+0.003/0.06)275 peff = 9.549 HVL (crn) = ln(2)/b 0.6931/9.549 = 0.0726 cm HVL (in) = HVL (cm)(0.3937 in/cm) = (0.0726)(0.3937) = 0.0286 in STD-EIA TEP177-A-E

34、NGL 1977 m 3234b00 058b14b 713 m TEP 197-A Page 4 X-radiation measurements made on the surface of the hypothetical cabinet shall be adjusted to the minimum specified glass thickness and minimum specified absorption, as follows in equation 5: x, =x.2L J where X is the measured exposure-rate (pA/kg) n

35、ormalized to the standard reference current for the tube type tested; XM is the maximum exposure-rate (pAkg) expected from the tube when the design parameters have been adjusted to minimum glass thickness and minimum absorption; p is the linear absorption coefficient (cm-) of the sample glass at a w

36、avelength of 60 pm; is the minimum specified linear absorption coefficient (cm-) of the glass at a wavelength of 60 Pm; t is the thickness (cm) of the sample glass at the location of maximum exposure-rate; tm is the minimum specified thickness (cm) of the sample glass at the location of maximum expo

37、sure-rate; HVL is the half-value layer-that increment of thickness (cm) of minimum absorption glass (for the given voltage) that attenuates the exposure rate to one-half of its value. EXAMPLE 2-A tube measures 0.72 pAikg at the standard reference current. What is the maximum hypothetical exposure ra

38、te (XM) that could be expected from this tube if it was constructed of glassware that has minimum specification for thickness and absorption? Other pertinent parameters are: p = 29.5 cm - t = 1 .O0 cm HVL = 0.0726 cm p = 28.0 cm - 1, = 0.93 cm (I(29.5)(1 .W)y28.0 - 0.93)/0.0726 X= 0.72 PNkg XM = (0.

39、72 pA/kg) 2 2.3 Data acquisition 2.3.1 Step 1 A minimum of six tubes of a given type are to be tested at 1 kV anode voltage intervals over a range of at least 5 kV. Preliminary analysis at the various measurement locations will help determine the range of voltages. To increase the accuracy of the ex

40、posure rate readings, particularly at the lower voltages, the use of high anode currents is recommended. The lower limit of the range may be determined by operating the tube at a high beam current then increasing the anode voltage until a significant exposure rate above background is attained. At th

41、e higher end of the anode voltage range the exposure rate should approach 36 pNkg. 2.3.2 Step 2 Measure the X-ray exposure rate (pA/kg) at the locations of maximum intensity, for each of the following TEP 197-A Page 5 Item Tube face Funnel Skirt Neck Anode contact areas of the hypothetical cabinet,

42、shown in figure 2, in accordance with the procedures in ANSVEIA-500 through ANSVEIA-503. Record the readings as X. CABINET TOP , Location Cabinet front Left, right, top, bottom or rear of cabinet Left, right, top or bottom of cabinet Rear or cone area of cabinet Top or side of cabinet PANEL SKIRT CO

43、NE CABINFP REAR CABINET BOTTOM Measure and record the glass thickness on the tube surface at location of maximum exposure-rate. An approximate area for measurement can be determined by shielding the tube surface with a nonconductive paddle which contains lead sheets. Reposition the paddle while obse

44、rving the meter indication of exposure rate. Note the paddle position which coincides with a minimum exposure rate. The glass thickness may be measured with an ultrasonic caliper, provided that the appropriate calibration for glass type has been performed The difference between the measured thicknes

45、s and the minimum specified thickness will be used to adjust the measured exposure rate to the minimum-pt situation. 2.3.4 Step 4 Determine the date code for the glass sample and obtain the linear absorption coefficient (LAC). The difference between the measured LAC and the minimum specified LAC wil

46、l be used to adjust the measured exposure rate to the minimum-pt situation. STD-EIA TEPL77-A-ENGL 2777 m 3234b00 05bL48 59b D TEP 1974 Page 6 2.3.5 Step 5 Adjust all exposure rate measurements standard anode current (IR) as follows: made at the nonstandard anode current levels (Id to the Color tubes

47、 (IR) = 300 pA Monochrome tubes (IR) = 250 pA Record as: XR = (300/IH)(X) or the geometric slope of the tangent line is the logarithm of the slope factor, .e., log SF = geometric slope. 3.1.6.1 Step 6a Locate the intersection of the average minimum - pt curve that was determined in 3.1.5 and the ano

48、de reference voltage. This intersection may not exist without extrapolation of the minimum pt curve (see first sentence in 3.1.6). 3.1.6.2 Step 6b Visually, determine the pNkg levels for the curve on either side of the reference anode voltage. The voltage difference (V2-V,) should be kept small, e.g

49、. ,200 volts or 400 volts depending on the anode voltage axis scale and the graph paper resolution. 3.1.6.3 Step 6c Calculate the slope factor from equation 6: 1 SF = antilog L where X2 corresponds to V2 and X, to VI. 3.1.7 Step 7 Construct the “X-radiation limit curve” through the 36 pAkg ordinate at the reference point anode voltage. Determine the second point by multiplying 36 pNkg by the slope factor. The pNkg result will be the ordinate position at the reference point anode voltage plus 1 kV. The straight line may be drawn with a straight edge. The