View
985
Download
1
Category
Tags:
Preview:
DESCRIPTION
PPT on Availability with respect to Reliability.
Citation preview
Availability with respect to Reliability
Significance of Availability
The Ability Of An Item To Perform A Required Function Under Stated Operating & Environmental Conditions For A Given Period Of Time.
A Percentage Measure Of The Degree To Which Machinery And Equipment Is In An Operable And Committable State At The Point In Time When It Is Needed.
Instantaneous (or Point) Availability
Average Up-Time Availability
Steady State Availability.
Inherent Availability
Achieved Availability
Operational Availability
AVAILABILITY CLASSIFICATIONS
Instantaneous (or point) availability is the probability
that a system (or component) will be operational (up and
running) at any random time.
Inherent availability is the steady state availability when considering only the corrective downtime of the system.
It is defined as the expected level of availability for the performance of corrective maintenance only.
Inherent availability is determined purely by the design of the equipment.
It assumes that spare parts and manpower are 100 percent available with no delays.
It excludes logistics time, waiting or administrative downtime, and preventive maintenance downtime.
It includes corrective maintenance downtime. Inherent availability is generally derived from analysis of an engineering design.
The probability that an item will operate satisfactorily at a given point in time when used under stated conditions in an ideal support environment (i.e., that personnel, tools, spares, etc. are instantaneously available).
It excludes logistics time and waiting or administrative downtime.
It includes active preventive and corrective maintenance downtime. Achieved availability is defined as the achieved level of availability for the performance of corrective and preventive maintenance.
Achieved availability is determined by the hard design of the equipment and the facility.
Also assumes that spare parts and manpower are 100 percent available with no delays.
Achieved availability is very similar to inherent availability with the exception that preventive maintenance (PM) downtimes are also included.
Availability = A = U/ U+D ; Where U = Up time ,
during which the machine is in working order; D =
Down time , During which the machine is faulty and
being repaired.
A = M/M+R = 1/ λ / (1/ λ +1/µ ) = µ/ µ+ λ ;
Where λ = failure rate = 1/M or M = 1/λ and R =
mean repair time . Repair rate = µ = 1/R or R = 1/ µ
Unavailability = B = D/ U+D
B = R/M+R = λ/ λ +µ.
A+B = (U/U+D + D/ U+D) = 1
TIME AVAILABILITY is the percentage of
operating time that an equipment is
operational
EQUIPMENT AVAILABILITY is the percentage
of equipments which will be available for use
after t hours of operation
MISSION AVAILABILITY is the percentage of
time t which will have any failure which
cannot be restored within a specified
maximum down-time
Recommended