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Some factors influencing reliability in analogue circuits for precision radar applications
254
ABSTRACTS ON ELECTRONICS RELIABILITY AND MICROMINIATURIZATION
Testing electronic equipment for power frequency noise. L. G. CLOUCH and J. A. SALZETTI, Electro-Technol., May 1963, p. 156. A method of simulating noise due to power distribution systems is described. The method permits laboratory checks on the susceptibility of electronic equipment to such noise. Reliability through redundancy in electro-mechanical devices. P. F. BECHBER~ER, derospace Engng., 21, Oct. 1962, p. 30. Shows how reliability in electromechanical devices can be improved with redundancy using an inertia reaction wheel as an example. The inertia reaction wheel has three main causes of failure: bearings, windings and case. The non-redundant failure probability in 10,000 hr was 2 per cent. Each bearing was replaced by a concentric, coplanar pair. If both rotate properly and if the cross-coupling of failures is negligible, then the failure probability will be very small (0.0032 per cent). The causes of bearing failure are discussed in relation to the redundancy. The causes of winding failure are given in relation to the modification of the windings and redundancy of the seal is also discussed at some length. T h e new failure probability was e3timated at 0"0043 per cent. Some factors influencing reliability in analogue circuits for precision radar applications. L. W. WHITAKERand D. H. CHANDLER,Marconi Rev., 25, 65 (1962). Discusses a new circuit technique to improve the precision and reliability of analogue circuits. Reliability: 1962. J. M. CARROLt., Electronics, 35, No. 48, Nov. 30, 1962 (p. 53). An excellent summary paper of the history and mathematics involved in reliability assessment. The Weibull Distribution is described and several reliability calculations made using tables given in the paper. Life testing is described in some detail and the Chi-Squared Distribution functions are illustrated by examples. Sequential testing is also described. A third section on Designing Reliable Circuits gives details of environmental de-rating curves and methods of calculating equipment reliability. A fourth section on Component Reliability covers most of the improvements which have been made in active and passive components. Definitions and brief descriptions are given of parallel redundancy, majority logic, time sequencing, on-air repair, value analysis, etc., and a final section is given on the Physics of Failure, which deals mainly with transistor failures and details some of the studies which have been made in this field. An excellent bibliography is provided. Estimation of life tests. R. FORSHU~VUD, Elektronik, 1, 70 (1963). In probability theory, the only probability distributions generally accepted are those of stochastic variables. Information theory allows a wider concept of probability. A probability distribution is assumed to exist for any quantity of which our knowledge is incomplete. A message generally makes a probability distribution narrower. In this paper, this wider probability concept is applied to the case of sample tests (of which life tests are a special case). The method is illustrated by some diagrams, computed for the case when the preliminary estimation is represented by a logarithmic normal distribution. RELIABILITY OF COMPONENTS, TUBES AND TRANSISTORS Practical procedure and results of reliability tests of transistors. H. W. HAGEMEISTER,Nachrichtentech. Fachber. (NTF), 24, p. 270 (1961). Discusses the problems of reliability tests, especially life expectation measurements. The most important and, against transistor variations, the most sensitive parameters are the reverse current - - I , and the current gain B. Failure rates of about 2.10 6h-1 seem to be typical for the tested transistor types. For applications in broadcast receivers this reliability seems to be satisfactory; for industrial or even telecommunication applications it is not. (In German.) Metal oxide film resistors. J. D. HAYDEN,Electron. Engng., Dec. 1962, p. 804. The oxide fihn resistor is examined against the background of increased reliability for fixed resistors and is discussed in relation to the designers' requirements, stability of the resistive film, its characteristics under prolonged usage for many years and the quality assurance which is likely to result from its application. Component reUability--a survey. G. W. A. DUMMER, Brit. Commun. Electron., June 1963, p. 434. Reliability remains one of the most important problems associated with components destined for military and industrial use. The author presents here some recently compiled facts, and some opinions on this questio n.
ABSTRACTS ON ELECTRONICS RELIABILITY AND MICROMINIATURIZATION
Testing electronic equipment for power frequency noise. L. G. CLOUCH and J. A. SALZETTI, Electro-Technol., May 1963, p. 156. A method of simulating noise due to power distribution systems is described. The method permits laboratory checks on the susceptibility of electronic equipment to such noise. Reliability through redundancy in electro-mechanical devices. P. F. BECHBER~ER, derospace Engng., 21, Oct. 1962, p. 30. Shows how reliability in electromechanical devices can be improved with redundancy using an inertia reaction wheel as an example. The inertia reaction wheel has three main causes of failure: bearings, windings and case. The non-redundant failure probability in 10,000 hr was 2 per cent. Each bearing was replaced by a concentric, coplanar pair. If both rotate properly and if the cross-coupling of failures is negligible, then the failure probability will be very small (0.0032 per cent). The causes of bearing failure are discussed in relation to the redundancy. The causes of winding failure are given in relation to the modification of the windings and redundancy of the seal is also discussed at some length. T h e new failure probability was e3timated at 0"0043 per cent. Some factors influencing reliability in analogue circuits for precision radar applications. L. W. WHITAKERand D. H. CHANDLER,Marconi Rev., 25, 65 (1962). Discusses a new circuit technique to improve the precision and reliability of analogue circuits. Reliability: 1962. J. M. CARROLt., Electronics, 35, No. 48, Nov. 30, 1962 (p. 53). An excellent summary paper of the history and mathematics involved in reliability assessment. The Weibull Distribution is described and several reliability calculations made using tables given in the paper. Life testing is described in some detail and the Chi-Squared Distribution functions are illustrated by examples. Sequential testing is also described. A third section on Designing Reliable Circuits gives details of environmental de-rating curves and methods of calculating equipment reliability. A fourth section on Component Reliability covers most of the improvements which have been made in active and passive components. Definitions and brief descriptions are given of parallel redundancy, majority logic, time sequencing, on-air repair, value analysis, etc., and a final section is given on the Physics of Failure, which deals mainly with transistor failures and details some of the studies which have been made in this field. An excellent bibliography is provided. Estimation of life tests. R. FORSHU~VUD, Elektronik, 1, 70 (1963). In probability theory, the only probability distributions generally accepted are those of stochastic variables. Information theory allows a wider concept of probability. A probability distribution is assumed to exist for any quantity of which our knowledge is incomplete. A message generally makes a probability distribution narrower. In this paper, this wider probability concept is applied to the case of sample tests (of which life tests are a special case). The method is illustrated by some diagrams, computed for the case when the preliminary estimation is represented by a logarithmic normal distribution. RELIABILITY OF COMPONENTS, TUBES AND TRANSISTORS Practical procedure and results of reliability tests of transistors. H. W. HAGEMEISTER,Nachrichtentech. Fachber. (NTF), 24, p. 270 (1961). Discusses the problems of reliability tests, especially life expectation measurements. The most important and, against transistor variations, the most sensitive parameters are the reverse current - - I , and the current gain B. Failure rates of about 2.10 6h-1 seem to be typical for the tested transistor types. For applications in broadcast receivers this reliability seems to be satisfactory; for industrial or even telecommunication applications it is not. (In German.) Metal oxide film resistors. J. D. HAYDEN,Electron. Engng., Dec. 1962, p. 804. The oxide fihn resistor is examined against the background of increased reliability for fixed resistors and is discussed in relation to the designers' requirements, stability of the resistive film, its characteristics under prolonged usage for many years and the quality assurance which is likely to result from its application. Component reUability--a survey. G. W. A. DUMMER, Brit. Commun. Electron., June 1963, p. 434. Reliability remains one of the most important problems associated with components destined for military and industrial use. The author presents here some recently compiled facts, and some opinions on this questio n.