Software Tips
Calculating The Number of Failures Using the PRICE HL Model
A common question asked recently is "What is the number of equipment failures calculated by the PRICE HL Model?" This is a key calculation within any hardware life cycle model. Each failure normally results in some sort of maintenance action, which results in not only maintenance costs, but also replenishment spare part costs, along with other associated costs.
The number of equipment failures can be easily calculated for individual line replacement units or modules, along with the number of failures at the system level. The number of failures can be calculated using one of two methodologies:
Number of system/equipment failures per year
Total number of system/equipment failure
The equation for calculating the number of system/equipment failures per year is:
Number of failures per year = (OTF * 8,766)/MTBF
| Where OTF | = | On Time Equipment Fraction |
| 8,766 | = | Number of Hours per year |
| MTBF | = | Mean Time Between Failures |
The above calculation results in the number of system/equipment failures per year. If total number of failures is desired than the below equation should be used:
Total number of failures = (OTF *8,766) * ED/MTBF
| Where OTF | = | On Time Equipment Fraction |
| 8,766 | = | Number of Hours per year |
| ED | = | Total Number of Equipment Deployed |
| MTBF | = | Mean Time Between Failures |
An example using the above equations is provided below for clarity.
| OTF | = | 0.5 |
| MTBF | = | 1000 |
| ED | = | 100 |
Number of failures per year = (0.5 * 8,766)/1000 or 4.38 failures per year. Total number of failures would then equal 438 over the life of the system.
The data required for the above equations can be obtained from the deployment element and MTBF information can be obtained from either the input window or from the system level output estimate window. Using the above equations provides a quick assessment to the number of failures being estimated across the hardware life cycle. Obviously this calculation is critical for completing Cost as an Independent Variable analysis.
