Circuit reliability (CiR) is the percentage of time

Time

Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 an electronic circuit

Electronic circuit

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

 was available for use in a specified period of scheduled availability

Availability

In telecommunications and reliability theory, the term availability has the following meanings:* The degree to which a system, subsystem, or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time...

. Circuit reliability

Reliability engineering

Reliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...

 is given by where T _o is the circuit total outage

Outage

Outage may refer to:* Network outage* Sun outage* Power outage* Outing...

 time, T_s is the circuit total scheduled time, and T _a is the circuit total available time.

In addition, circuit reliability is the expected lifespan of operation of a functioning system under nominal conditions.