BS ISO 18927:2013 pdf free download.Imaging materials — Recordable compact disc systems — Method for estimating the life expectancy based on the effects of temperature and relative humidity.
BS ISO 18927 specifies a test method for estimating the life expectancy or information stored on recordable compact disc systems. Only the effects of tcmperawre and relative humidity on the media are considered.
BS ISO 18927 does not cover the effects of light, air pollution, or time-dependent flow phenomena.
2 Normative references
The following documents. In whole or In part, are normatively referent-ed in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC1O149’ ), Infonnadon technology — Data interchange on read-only l2Ommoptlcal data dlsks(CD-ROM)
IEC 60908. Audio recording — Compact disc digital audio system
Experimental statistics. US. National Bureau of Standards Handbook 91.1963
3 Terms and deilnitions
For the purposes of this document, the following terms and definitions apply.
3.1
baseline
condition representing the disc at time of manufacture
Note Ito entry: This Is customarily the initial parameter measurement taken prior to any appikatlon Distress, The designation is usually t • 0 for a stress time equal to zero hours.
block error rate
BIER
ratio of erroneous blocks to total blocks measured at the Input of the first (Cl) decoder(beiore any error correction is applied)
Note I to entry: The more commonly reported value for tILER is the number of erroneous blocks pe second measured at the input of the Cl-decoder during playback at the standard (IX) data rate.
[IEC 609081
3.2.1
maximum block error rate max BLER
maximum tILER measured anywhere on a disc
3.8.1
glass transition temperature
approximate mid-point of the temperature range over which glass transition takes place
Note I to entry: T1can be determined readily only by observing the temperature at which a significant change takes place In a specific electrical, mechanical. or other physical property.
Note 2 to entry: T1can also be sens.tlve to the moisture content nithe polymer.
3.9
Information
signal or Image recorded using the system
3.10
life expectancy
LE
length of time that Information is predicted to be acceptable in a system after dark storage at 23 C and
50% relative humidity (RH)
3.10.1
standardized lire expectancy
SLE
minimum life span, predicted with 95% confidence. ci 95% of the product stored at a temperature not exceeding 25 C and a relative humidity (RH) not exceeding 50% RH
3.11
retrievability
ability to access nformation as recorded
3.12
stress
experimental variable to which the specimen is exposed for the duration of the test interval
Nor1
3.13
survivor function
probability that .i random unit drawn from the population survives at least time t, or the fraction of all units in the population which survive at least time I
Note Ito entry: R(t) = 1— F(t).
3.14
system
combination of material, hardware, software, and documentation necessary for recording and/or retrieving information
3.15
test cell
device that controls the stress to which the specimen Ls exposed
3.16
track-at-once recording
method of recording a CD-R disc whereby each track Is recorded Individually with 150 empty sectors Immediately preceding It and two run-out sectors Immediately following
uncorrectable error
error in the playback data that is not correctable by the cross interleave Reed-Solomon code defined in IEC 60908 as implemented in a system
4 Purpose and assumptions
4.1 Purpose
The purpose of BS ISO 18927 is to establish a methodology for estimateng the life expectancy of information stored on recordable compact disc systems. This methodology provides a technically and statistically sound procedure for obtaining and evaluating accelerated test data.
The methodology deals only with the effects of temperature and humidity on the retrievability of stored Information. For this reason, BS ISO 18927 Is primarily directed to those storage applications, e.g. libraries and archives, in which exposure to other influences potentially detrimental to information life expectancy, such as chemical agents, intense light sources, and improper handling, Is controlled and minimized.
4.2 Assumptions
The validity of the procedure defined by this International Standard relies on three assumptions:
— specimen life distribution is appropriately modelled by the lognormal distribution:
— the kinetics of the dominant failure mechanism is appropriately modelled by an Eyring acceleration model;
— the dominant failure mechanism acting at the usage condition is the same as that at the accelerated conditions.
Publications by Hamada and Stinson provide data indicating that these assumptions are applicable to compact disc-recordable (CD-R) systems (see references(J andIj in the Bibliography).
5 Measurements
5.1 Summary
A sampling of 80 recorded discs shall be divided Into five groups according to a specified plan. Each group of discs (test cell) shall be subjected to one of five test stresses, combinations of temperature and relative humidity. Periodically during the stress conditions, all discs from each stress group shall have their block error rate (BIER) measured. Data collected at each time interval for each individual disc are then used to determine a lifetime for that disc.
The disc lifetimes at each stress level are fitted to a lognormal distribution to determine a mean lifetime for the stress. The resulting five mean lifetimes are regressed against temperature and relative humidity according to an Eyrlng acceleration model, This model is then used to estimate the distribution of lifetimes at a usage condition.
5.2 Block error rate (BLF.R)
End-of-life Is the occurrence of any loss of Information. Ideally, each specimen Is tested until the first loss of information occurs. Realistically, this Is Impractical. This International Standard considers max BIER to be a hlgh.level estimate of the performance of the systent The objective of measuring BIER Is to establish a practical estimation of the system’s ability to read recorded data without uncorrectable errors. A change in max BIER in response to the time at an accelerated temperature and humidity is the principal quality parameter.
7.3 AcceleratIon factors
Once the log mean and log standard deviation have been determined for each acceleration stress, then the Eyrlng model shall be solved by a regression oltemperature, relative humidity, and log mean to determine the estimated log mean at the storage or usage condition of interest (25°C and 50 % RH). The difference between the usage log mean and the accelerated stress log mean Is used to compute the acceleration factor for that stress relative to the usage condition, such that the acceleration factor Is e
By multiplying the failure times at each accelerated stress condition by the acceleration factor for that stress condition, the data are normalized to the usage condition. This normalized data shall then be plotted on the same lognormal distribution graph to determine the estimated distribution of failures at the usage condition.
7.4 Survivor analysis
Once the failure distribution F(t) is known for time , then the survival fraction R(t) shall be calculated from the relationship (R(t) 1— F(t)]. From its definition. R(t) Is the probability that any given disc will survive at least time t, or the percentage of the entire population that will survive at least time t.
A plot of the survival fraction R(t) versus time Is useful for graphically representing the characteristics of the specimens tested. The confidence Intervals of the survivor fraction shall be calculated using the method of asymptotic normal approximation. From these results, one shall state the fraction of product surviving at least time t, the statistical confidence level used, and the storage temperature and relative humidity combination chosen for the model.
The life expectancy statement shall indicate the caveat that only the effects of temperature and humidity are Included. For a standardized life expectancy (SLE), this would read: At a storage condition of 25 °C and 50 % RH, 95 % of the product evaluated will last a minimum of x years with 95 % confidence, considering only the effects of temperature and relative humidity.
7.5 Aids
A listing of computer packages, along with their key features, that may be useful for life expectancy data analysis is given by Nelson (see pages 237 to 239 of Referencel7l in the Bibliography). Equivalent software may be used.
Annex Li shows an example of a CD.R media life expectancy calculation
8 Disclaimer
Using this model, the standardized life expectancy (SLE) Is defined For discs maintained at 25 °C and 50 % Rh. Discs exposed to more severe conditions of temperature and humidity are expected to experience a shorter life.
The test method specified In BS ISO 18927 does not attempt to model degradation due to exposure to light, corrosive gases, contaminants, mishandling, and variations in the playback system.