The Contributions of Edsel Murphy to the Understanding of the Behaviour of Inani

Abstract - Consideration is given to the effects of the contributions of Edsel Murphy to the discipline of electronics engineering. His law is stated in both general and special form. Examples are presented to corroborate the author's thesis that the law is universally applicable.

1. Introduction

It has long been the consideration of the author that the contributions of Edsel Murphy, specifically his general and special laws delineating the behaviour of inanimate objects, have not been fully appreciated. It is deemed that this is, in large part, due to the inherent simplicity of the law itself.

It is the intent of the author to show, by references drawn from the literature, that the law of Murphy has produced numerous corollaries. It is hoped that by noting these examples, the reader may obtain a greater appreciation of Edsel Murphy's law, and its ramifications in engineering and science.

As is well known to those versed in the state - of -the - art, Murphy's Law states that " if anything can go wrong, it will. " Or, to state it then in more exact mathematical form:

1+1 #= 2 ¹

(1) where #= is the mathematical symbol for hardly ever.

Some authorities have held Murphy's Law was first expounded by H. Cohen ¹ when he stated that "if anything can go wrong, it will - - during the demonstration." However, Cohen has made it clear that the broader scope of Murphy's general law obviously takes precedence. To show the all - pervasive nature of Murphy's work, he also offers a small sample of the application of the law in electronics engineering.

2. General Engineering

2. 1. The patent application will be preceded by one week by a similar application made by an independent worker.

2.2. The more innocuous the design change appears, the further its influence will extend.

2.3. All warranty and guarantee causes become void upon payment of invoice.

2.4. The necessity of making a major design change increases as the fabrication of the system approaches completion.

2.5. Firmness of delivery dates is inversely proportional to the tightness of the schedule.

2.6. Dimensions will always be expressed in the least usable term. Velocity, for example, will be expressed in furlongs per fortnight.

2.7. An important instruction manual or operating manual will have been discarded by the Receiving Department.

2.8. Suggestions made by the Value Analysis group will increase costs and reduce capabilities.

2.9. Original drawings will be mangled by the copying machine. ³

3. Mathematics

3.1. In any given miscalculation, the fault will never be placed if more than one person is involved.

3.2. Any error that can creep in, will. It will be in the direction that will do most damage to the calculation.

3.3. All constants are variables.

3.4. In any given computation, the figure that is most obviously correct will be the source of error.

3.5. A decimal will always be misplaced.

3.6. In a complex calculation, one factor from the numerator will always move into the denominator.

4. Prototyping and Production

4.1. Any wire cut to length will be too short.

4.2. Tolerances will accumulate unidirectionally toward maximum difficulty of assembly.

4.3. Identical units tested under identical conditions will not be identical in the field.

4.4. The availability of a component is inversely proportional to the need for that component.

4.5. If a project requires n components, there will be n -1 units in stock. ⁴

4.6. If a particular resistance is needed, that value will not be available. Further, it cannot be developed with any available series or parallel combination. ⁵

4.7. A dropped tool will land where it can do the most damage. (Also known as the law of selective gravity.)

4.8. A device selected at random from a group having 99 % reliability, will be a member of the 1% group.

4.9. When one connects a 3-phase line, the phase sequence will be wrong. ⁶

4.10. A motor will rotate in the wrong direction. ⁷

4.11. The probability of a dimension being omitted from a plan or drawing is directly proportional to its importance.

4.12. Interchangeable parts won't.

4 13. Probability of failure of a component, assembly, subsystem or system is inversely proportional to ease of repair or replacement.

4.14. If a prototype functions perfectly, subsequent production units will malfunction.

4.15. Components that must not and cannot be assembled improperly will be.

4.16. A do meter will be used on an overly sensitive range and will be wired in ^backwards.8

4.17. The most delicate components will drop. ⁹

4.18. Graphic recorders will deposit more ink on humans than on paper. ¹⁰

4.19. If a circuit cannot fail, it will. ¹¹

4.20 A fail-safe circuit will destroy others. ¹²

4.21. An instantaneous power - supply crowbar circuit will operate too late. ¹³

4.22 A transistor protected by a fast -acting fuse will protect the fuse by blowing first. ¹⁴

4.23. A self - starting oscillator won't.

4.24. A crystal oscillator will oscillate at the wrong frequency - - if it oscillates.

4.25. A PnP transistor will be an nPn. ¹⁵

4 26. A failure will not appear until the unit has passed final inspection. ¹⁶

4.27. A purchased component or instrument will meet its specs long enough, and only long enough, to pass incoming inspection. ¹⁷

4 28. A zero - temperature - coefficient capacitor used in a critical circuit will have a TC of minus 750 ppm / degrees centigrade.

4.29. If an obviously defective component is replaced in an instrument with an intermittent fault, THE FAULT.

4.30. After the last of 16 mounting screws has been removed from an access cover, it will be discovered that the wrong access cover has been removed. ¹⁹

4.31. After an access cover has been secured by 16 hold - down screws, it will be discovered that the gasket has been omitted. ²⁰

4.32. After an instrument has been fully assembled, extra components will be the be found on the bench.

4.33. Hermetic seals will leak.

5. Specifying

5.1. Specified environmental conditions will always be exceeded.

5.2. Any safety factor set as a result of practical experience will be exceeded.

5.3. Manufacturers' spec sheets will be incorrect by a factor of 0-5 or 2.0, depending on which multiplier gives the most optimistic value. For salesman's claims these factors will be 0.1 or 10.0.

5.4. In an instrument or device characterized by number of plus - or - minus errors, the total error will be the sum of all errors adding in the same direction.

5.5. In any given price estimate, cost of equipment will exceed estimates by a factor of three.

5.6. In specifications, Murphy's law supersedes Ohm's.

References

[1] H. Chen, Roundhill Associates, private communication

[2] P. Birzman, Kepco, private communication

[3] T. Emma, Western Union, private communication

[4] ---, loc cit

[5] ---, loc cit

[6] ---, loc cit

[7] ---, loc cit

[8] P. Muchnick, Sorenson, private communication

[9] A. Rosenfield, Micro Power, private communication

[10] P. Muchnick, loc cit

[11] R. Cushman, McCann, ITSM, private communication

[12] ---, loc cit

[13] ---, loc cit

[14] S. Froud, Industrial Communication Associates, private communication

[15] I. LeVieux, Texas Instruments, private communication

[16] G. Toner, Sylvania, private communication

[17] H. Roth, Power designs, private communication

[18] W. Buck, Marconi Instruments, private communication

[19] A. de la Lastra, SBD systems, private communication

[20] ---, loc cit

[21] P. Dietz, Data Technology, private communication

In some cases where no reference is given, the source material was misplaced during preparation of this paper (another example of Murphy’s Law). In accordance with the law, these misplaced documents will turn up on the date of publication of this paper.