ISO IEC 10995:2011 pdf – lnformation technology -Digitally recorded media for information interchange and storage- Test method for the estimation of the archival lifetime of optical media.
8.3 Measuring Time intervals
For data collection, P1 Sum 8 (DVD-R, DVD-RW, +R, +RW), or BER (DVD-RAM) measurements for each disk will occur: 1) before disk exposure to any stress condition to determine its baseline measurement and 2) after each cycle ol incubation. The length or time for intervais is dependent on the severity of the stress condition.
Using each disks regression equation, the failure time for each disk shall then be computed for the stress condition it was exposed to.
8.4 Stress Conditions Design
Table 2 specifies the temperatures, relative humidities, time intervals, minimum total test time, and minimum number of specimens for each stress condition. A separate group of specimens is used for each stress condition.
All temperatures may deviate ±2 ‘C of the target temperature; all relative humidities may deviate ±3 % RH of the target relative humidity.
The intermediate relative humidity (RH) in Table 2 is calculated assuming 25 C and 50 % RH ambient conditions. If the ambient is different, the intermediate relative humidity to be used is calculated using the equation:
where: T and T, are the ambient and incubation temperature in units of ‘C; ii is the ambient relative humidity;
RH1 is the intermediate relative humidity.
The stress conditions tabijated in Tables 2 and 3 offer sufficient combinations of temperature and relative humidity to satisfy the mathematical requirements of the Eyring model to demonstrate linearity of either Max P1 Sum 8. or Max BER or their logs respectively, versus time, and to produce a satisfactory confidence level to make a meaningfii conclusion.
8.5 Media Orientation
Media subjected to this test method shall be maintained in a vertical position with a minimum of 2 mm separation between disks to allow air flow between disks and to minimize deposition of debris on disk surfaces which could negatively influence the error rate measurements,
9 Data Evaluation
9.1 Time-to-failure
All disks subjected to stress conditions shall have their time-to-failure calculated at the stress condition they have been subjected to. Failure criteria values are: Max P1 Sum 8 exceedIng 280 for DVD-RIRW. +Ri+RW. and Max BER exceeding i03 for DVD-RAM,
Material degradation manifests itself as data errors in the disk, providing a relationship between disk errors and material degradation. The chemical changes are generally expected to cause test data to have a distribution that follows an exponential function over time. Therefore, test data values of: P1 Sum 8 or BER as a function of time are expected to exhibit an exponential distribution.
The following is an outline of steps to estimate the life expectancy value, as a function of ambient temperature and relative humidity, and used to determine if a disk will or will not exceed a life expectancy of X.years,
For each specimen, compute (via linear regression), the predicted time-to-failure.
2. (Steps 2 and 3 are for data quality check)
For each stress condition, determine the median rank of each specimen, and plot the median rank versus time-to-failure on a lognormal graph.
3. Verify that the plots tot all stress conditions are reasonably parallel to one another.
NOTE In the case where the plots are not delermned to be reasonably paralel, 7.1.2 Assumptions stiall be checked
4. Using the reduced Eyring equation, carry out a least squares M to the log failure times across all specimens and stress conditions.
5. Calculate acceleration factors for each stress condition.
6. For the ambient condition, calculate normalized time-to-failure for each disk.
For the ambient condition, calculate 95 % survival probability with 95 % confidence for lifetime.