11.3.2 Systems with more than two components
Unlike the case of series systems, it is not possible to extend easily the equations for a 2-component parallel system to a general n-component system.
It is possible in certain systems to combine two components at a time using Equations 11.15 to 11.18. This method must be treated with the utmost care because it becomes invalid if the concepts of a single failure rate per component, or a single environmental state. are extended to more complex situations. It is better to use an appropriate set of equations for the number of components that require combining.
It is evident that such equations can be deduced from first principles using the concepts of Sections 11.3.1. It is simple to deduce the equations from the logic of Equations 11.15 to 11.18. In order to understand this logic, rewrite Equation 11.17 in the from
This equation may be expressed in words as:
“failure of the system occurs if (component 1 fails followed by failure of component 2 during the repair time of component 1) or (component 2 fails followed by failure of component 1 during the repair time of component 2)”
The product terms contained by the parentheses in Equation 11.19 represent the probability that one component fails during the outage time of the other; this condition being the only way in which a parallel system can fail. The “time” during which the associated component must fail for the system to fail.
Using this logic the expression for the failure rate of a system containing three or more components can be deduced. Consider for example, the case of a three component (A,B and C ) parallel system. In this case the failure expression is:
“failure of the system occurs if
(A fails followed by failure of B during repair of A followed by failure of C during the overlapping repair of A and B) OR
(A fails followed by failure of C during repair of A followed by failure of B during the overlapping repair of A and C) OR
(Pluse 4 more similar statements for the failure sequences BAC,BCA,CAB,CBA)”
11.3.2 Systems with more than two components
Unlike the case of series systems, it is not possible to extend easily the equations for a 2-component parallel system to a general n-component system.
It is possible in certain systems to combine two components at a time using Equations 11.15 to 11.18. This method must be treated with the utmost care because it becomes invalid if the concepts of a single failure rate per component, or a single environmental state. are extended to more complex situations. It is better to use an appropriate set of equations for the number of components that require combining.
It is evident that such equations can be deduced from first principles using the concepts of Sections 11.3.1. It is simple to deduce the equations from the logic of Equations 11.15 to 11.18. In order to understand this logic, rewrite Equation 11.17 in the from
This equation may be expressed in words as:
“failure of the system occurs if (component 1 fails followed by failure of component 2 during the repair time of component 1) or (component 2 fails followed by failure of component 1 during the repair time of component 2)”
The product terms contained by the parentheses in Equation 11.19 represent the probability that one component fails during the outage time of the other; this condition being the only way in which a parallel system can fail. The “time” during which the associated component must fail for the system to fail.
Using this logic the expression for the failure rate of a system containing three or more components can be deduced. Consider for example, the case of a three component (A,B and C ) parallel system. In this case the failure expression is:
“failure of the system occurs if
(A fails followed by failure of B during repair of A followed by failure of C during the overlapping repair of A and B) OR
(A fails followed by failure of C during repair of A followed by failure of B during the overlapping repair of A and C) OR
(Pluse 4 more similar statements for the failure sequences BAC,BCA,CAB,CBA)”
การแปล กรุณารอสักครู่..