Converting From Calendar Hours to Operating Hours
Traditionally, reliability prediction failure rate models have been based on the operating time of the part, and the values were typically stated in failures per million (or billion) operating hours. The 217Plus™ component models (and the empirical data contained in the databases used in the 217Plus™ tool) predict the failure rate in units of failures per million calendar hours. This is necessary because it represents the common basis for all the failure rate contribution terms used in the 217Plus™ methodology (e.g., operating, non-operating, cycling, and induced). If an equivalent operating failure rate is desired (in units of failures per million operating hours) steps need to be taken to make this conversion.
To convert a 217Plus™ analysis from Calendar to Operating hours the resulting 217Plus™ predicted failure rate (based on the expected duty cycle) should be divided by the duty cycle in its decimal form (e.g., A 50% duty cycle = 0.5). It would be incorrect to assume a 100% duty cycle for the system (unless the system actually operates at 100% duty cycle) as factors that influence reliability, such as cycling and non-operation, would be not be properly addressed.
For more information on 217Plus™, feel free to contact the 217Plus™ team by phone (315-351-4202) or by E-mail (inquiry@theRIAC.org).
To obtain additional information including a demo version of the software, go to (http://theRIAC.org/ProductsAndServices/Products/217Plus/index.asp).