SNT Reliability Analysis
Mean-Time-Between-Failures (MTBF) is one of the most widely used measures of device reliability.
rm
MTBF figures are used to schedule routine maintenance, determine the requirements for backup equipment, compare the reliability of a given device to industry or installation standards, or aid in the selection of competing equipment models.
Tracking the rate of change of MTBF statistics over time can also yield valuable results. Decreasing MTBF values can foreshadow the end of the practical useful life of a device. Conversely, increasing MTBF values are sometimes encountered in installations which utilize heavily microcoded, "intelligent" devices such as point-of-sale or financial controllers. These devices may experience random hard failures due to undiscovered microcode errors. A significant increase in MTBF following a microcode update may indicate that such a "bug" was fixed.
MTBF statistics are easily reported using the data retained by
MICS
in the NPDA Event (SNTNEF) File. Each entry in this file in the DETAIL time-span records the occurrence of a permanent error on a specific device. In the higher timespans (DAYS, WEEKS, MONTHS, and YEARS), the number of failures of a given type are summarized for each device in the variable Number of Events (NEFNREVT). Since basic MTBF statistics are based on the total number of failures, the data must be summarized across all types of failures. This can easily be done using the MICS
Summarization Facility as follows:%INCLUDE INCLLIB(#SNTSUM); MACRO _BY NEFFRNAM % MACRO _BREAK NEFFRNAM % PROC SORT DATA=_dSNTM.SNTNEF01 OUT=MTBF; BY _BY; RUN; DATA MTBF; SET MTBF; BY _BY; _NEFSUM RUN; DATA MTBF (KEEP=NEFFRNAM MTBF); FORMAT MTBF TIME.; LABEL MTBF=MEAN-TIME-BETWEEN-FAILURES; MTBF = (ENDTS-STARTTS) / NEFNREVT; RUN; PROC PRINT LABEL; VAR NEFFRNAM MTBF; TITLE1 'MEAN-TIME-BETWEEN-FAILURE STATISTICS'; RUN;