**RELIABILITY** — property of any object (a detail, a component, a product, system, body, etc.) to perform certain functions, keeping the indicators in the set limits during a required time term. N.'s disturbance, or failure, is characterized by falloff of operability of any object.

In medicine the problem H. is of great importance in relation to the measuring devices and devices used in diagnosis, therapy, etc. for obtaining exact information on objects of a research, and especially for ensuring reliable functioning artificial organs (see) and devices.

Definition of characteristics of N. and their analysis is carried out on the basis of information on work and failures of objects during their normal operation or during their development and carrying out tests. Researches H. are based on use of methods of probability theory and mathematical statistics (see. Probabilities theory , Mathematical methods ).

The main characteristic of N. of objects is probability of no failure of p(t), i.e. probability that under the set service conditions in a time slice of t the failure will not come.

The N can be characterized also by rejection probability of q(t), i.e. probability that in the set time slice there will be at least one failure.

The important characteristic of N. is mean time of no-failure operation, or the mathematical expectation of time of no-failure operation calculated by a formula:

where Tsr — mean time of no-failure operation; p(t) — probability of no failure; dt — an interval of time, relatively to-rogo conduct

calculation; — the sum of p(t) dt values is ranging from zero (0) indefinitely (∞).

The failure — the phenomenon accidental, however its emergence is caused by a row physical or physical. - the chemical processes proceeding in objects at various stages of their functioning in time. As an accidental event failures can be dependent when emergence of failure of one element leads to failure of others, and independent if the failure of an element does not serve as a cause of failure of other elements in system.

The analysis of failures, knowledge of their physical essence and emergence allow to make a right choice of materials for production of objects, to provide necessary measures for protection them from influence of external factors (ambient temperature, pressure, humidity, vibration, magnetic fields, etc.), to use the constructive decisions allowing to receive necessary or possible N. of an object, etc.

Tests of objects for N. are subdivided on attributive and control. Attributive are carried out for the new or modernized objects on test pieces, control — for serially produced objects for the purpose of definition of compliance of indicators of N. to qualifying standards. Assessment of test data on N. is made by method of simple sampling, to-ry is that N.'s assessment of an object is carried out after tests of in advance accepted volume of selection, or by a consecutive method — N.'s assessment is made after each observation (emergence of failure or other).

N.'s providing is connected with all stages of creation and operation of an object. At design of objects are considered: quality and a duty of the applied components, details and materials, from to-rykh they are made; a possibility of access for survey, control, repair or replacement of the components which are a part of an object; creation of special protective measures, the most important of to-rykh is the reservation based on introduction of reserve parts, excessive in relation to the minimum functional structure of an object necessary and the sufficient for performance set functions and the preventive corrective maintenance providing maintenance of operability of an object in the course of its functioning for increase in N.

By production of objects a number of conditions on maintenance tekhnol, disciplines and to observance of the modes tekhnol shall be executed. processes of their production.

**Bibliography:** Sotskov B. S. Bases of the theory and calculation of reliability of elements and devices of automatic equipment and computer facilities, M., 1970; Chervony A. A., Lukyashchenko V. I. and Kotin L. V. Nadezhnost of complex systems, M., 1976, bibliogr.

*I. K. Petrov.*