716 MECHANICAL DESIGN AND PACKAGING 



probability that a system will give satisfactory performance for a given period 

 of time when used in the manner and for the purpose intended. 



From this definition, it is clear why reliability is a system parameter of 

 paramount importance. The success or failure of a military mission turns 

 on the ability of equipments to carry out assigned functions. Regardless of 

 the degree of sophistication of the equipments, or the high performance of 

 which they are theoretically capable, their potential value to a military 

 commander is strictly a function of the probabilities that they will operate 

 satisfactorily when called on. 



In this section we shall consider various aspects of the reliability problem 

 of which the system designer must be aware in his designs. Specifically, we 

 shall be concerned with the influence of reliability on system planning, the 

 factors which affect reliability of electronic equipment, how to attain 

 satisfactory reliability, how reliability is measured, and how it may be 

 quantitatively predicted. 



Reliability and System Planning. Reliability is a basic system 

 performance parameter. As shown in Paragraph 2-23 the specification of 

 reliability forms a part of the system requirements as dictated by the 

 tactical mission requirements. This material also illustrated the more-or- 

 less direct relationship between reliability and the attainable level of 

 mission accomplishment. 



The derived reliability requirement represented an estimate of a relia- 

 bility goal that would — in combination with the goals set for other aspects 

 of system operation (detection, vectoring, etc.) — allow the system to 

 fulfill its overall mission objectives. 



With requirements generated, we are ready to examine the specific factors 

 which influence the attainment of the reliability objective. 



Factors Which Influence Reliability. The final reliability of an 

 electronic equipment is a function of many interacting and only incom- 

 pletely understood factors. Some of these factors are listed here. 



1. The detail design and fabrication of the electrical and mechanical 

 components used in the system. 



2. The application of the individual components in the equipment. 



3. The methods of manufacture and assembly of the equipment, 

 including quality control and inspection techniques. 



4. The simplicity of the design for field maintenance as well as the 

 maintenance facilities available. 



5. The abilities and skills of the military personnel who operate and 

 maintain the equipments. 



6. The physical environmental conditions operating on the equipment, 

 such as temperature, shock, altitude, etc. 



