The starting time for the calculations in hours. The start time and end time specify the time range for the calculations. This range of time is intended to represent the period of time that the system is operating.

The end time for the calculations in hours.

The number of calculations to perform within the specified period of time. For instance, if the range of time is from 0 to 300 and the number of data points is 3, then 3 calculations run in the 300 hours. In this example, calculations are performed at 0 hours, 150 hours, and 300 hours.

The results at this time are shown on the General page under RBD in the View Calculation Results window once calculations are completed. They appear under Results at time < value >. They are also shown in the RBD Results label if it is inserted in the diagram. For more information, see Inserting an RBD Results Label to Display System Calculation Results.

The capacity or output that the system is required to meet to be considered operating. If the capacity falls below this number, the system is considered failed even though it may still be working physically. This causes the costs assigned on the Downtime page to be incurred appropriately. For more information, see Downtime Page. If this value is zero, then capacity does not affect system availability.

The probability that the system will remain operational until a specified time. Reliability is a time-based probability value, which means it has a value between 0 and 1. A reliability of 0 means that the system always fails before the specified time or never functions until the specified time. A reliability value of 1 indicates that a system always operates until the specified time. For more information, see Reliability Calculations.

The MTTF is the mean or average time to failure in hours. For repairable systems, it is the average time to reach the first system failure. Hence, it is also called the MTTFF (mean time to first failure). For more information, see MTTF Calculations.

The rate at which the system fails at time t. For more information, see Failure Rate Calculations.

The equivalent failure rate of the system based on the cumulative probability. For more information, see Equivalent Failure Rate Calculations.

When cleared (default) repairs are not considered when calculating reliability values. When selected, repairs are performed on individual components until the system fails. This usually requires simulation. For more information, see Reliability With Repair.

The probability that the system is operating properly at a specified time. Availability, like reliability, is a time-based probability metric, so its value is always between 0 and 1. It is also called point availability or instantaneous availability.

Either inherent availability or operational availability can be calculated at a given time. Availability is a function of both reliability (how quickly the system fails) and maintainability (how quickly the system is repaired). A common term, “five nines,” refers to a system having an availability of 0.99999. Such a system is operational 99.999% of the time. If any repairable components are not repairable online, availability is simulated. When this checkbox rather than Operational availability is selected, logistic delay times are ignored when computing all of the results in this section and when computing cost-related results for the system. For more information, see Availability Calculations.

The MTBF (mean time between failures) represents the mean number of hours between two consecutive system failures in a long run. For more information, see MTBF Calculations. The run length is specified by Number of system failures to reach steady state, which appears on the Advanced page in the Calculate window. For more information, see Advanced Page.

The effective MTBF refers to when a component or system is subjected to a periodic replacement. It is the time between unplanned maintenances due to a failure. The effective MTBF depends on the periodic replacement/maintenance interval, T. For any given T, the times between in-service failures have random durations. The expected value of the time between failures is equal to MTBF. Effective MTBF can be viewed as the MTBF in a long run or in the steady state.

The MTTR (mean time to repair) is the average time it takes to repair a failed system and return it to an operational state, based on the repair time distributions for its repairable blocks. The MTTR can be calculated by considering the frequency of each failure scenario and its respective average repair times. Mathematically, it is equivalent to:

Where:

For non-repairable systems, the hazard rate, or conditional failure intensity, is equivalent to the failure rate. For repairable systems, the hazard rate is equivalent to the rate of failure of the system at a specified time given that the system is operational at that time. For more information, see Hazard Rate Calculations.

The average availability over a specified time interval. Mean availability is the ratio of the mean total uptime to the total time over a specified interval. For more information, see Mean Availability Calculations.

The availability of the system over a long run, or as time tends to infinity. Steady state availability is the ratio of the total uptime to total time in a long run. For more information, see Availability Calculations. The run length is specified by Number of system failures to reach steady state, which appears on the Advanced page in the Calculate window. For more information, see Advanced Page.

The total downtime during the specified interval. For more information, see Total Downtime Calculations.

The total number of failures expected between the indicated start time and end time. For more information, see Number of Failures Calculations.

Expected number of failures per unit time at a specified time. For more information, see Failure Frequency Calculations.

The probability that an item is in an operable state at any time. When operational availability is calculated, logistic delay times are included when computing all of the results in this section and also when computing cost-related results for the system. For more information, see Availability Calculations.

The expected capacity or output of the system. For more information, see Capacity Calculations.

Indicates whether to identify the collection of components such that if all of these components fail, the system fails. When this checkbox is cleared, cut sets are not calculated. When it is selected, cut sets are calculated. Cut sets are not used in computation algorithms. They are for informational purposes only.

Indicates whether to identify the collection of components such that if all of these components operate, the system operates. When this checkbox is cleared (default), path sets are not calculated. When it is selected, path sets are calculated. Path sets are not used in computation algorithms. They are for informational purposes only.

The probability value that determines whether to show a cut set. 0, 1e-30, 1e-25, 1e-20, 1e-15, 1e-10, and 1e-5. The default is 0. You can also type a probability value in this field.

The number of blocks to use to determine whether to show a cut set. The default for this field is a number sign (#), which indicates that no limit exists on the number of blocks.

Indicates whether to calculate cost-related results for the system and its diagram blocks, including spares. When this checkbox is cleared (default), cost calculations do not run. When it is selected, cost calculations do run. If availability is calculated, cost calculations ignore logistic delay times. If operational availability is calculated, cost calculations take logistic delay times into account.

Indicates whether to show the analytical equation used to calculate reliability on the Reliability Equations Results page under RBD in the View Calculation Results window. When this checkbox is cleared (default), no equation is shown. When it is selected, an equation is shown unless all results are simulated. If all results are simulated, no equation can be shown. For more information, see Equation Page.