| The information provided by many fan manufacturers is often vague and makes an immediate comparison impossible. The different measuring units applied worldwide for pressure and airflow rate do not permit a simple comparison. In particular, the quoted service life is frequently so imprecise that a true assessment of quality is impossible.
The service life of a component depends to a great extent on many factors and varies widely so that it cannot be defined precisely. Service life figures of-ten mentioned in data sheets refer to the probability of survival. In order to interpret them correctly, one must be acquainted with the conditions that this sta-tistical value were based on: 1. Probability factor (L1, L10 or MTBF) |
The MTBF is also frequently quoted. This is the mean period between two errors. As far as fans are concerned an error is equivalent to failure, therefore one should actually refer to MTTF (Mean Time To First Failure). The MTBF of SEPA fans is based on a probability of failure of 63%. L1, L10, MTBF and MTTF are statistical values that can only be determined by observing large quantities over a long period of time. With individual delivery batches, a deviation is possible in both directions. Only when many delivery batches are evaluated, is concurrence with the predicted value high. The values L1, L10 and MTBF can be regarded as rough values in the following example: L1 : L10 : MTBF = 0.21 : 1.0 : 4.0
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*) Temperature of the heat sink 60°C. Air temperature 40°C
Table 1: Comparison of probability of service life and probable failures at TU=60°C
| Failures do not normally occur at regular intervals during the service life. The so-called „bath-tub curve life“ applies, i.e. relatively high probability of failure after short operating period. In order to minimise these particularly unpleasant early failures, all SEPA® fans are subject to a 12-hour burn-in at an average temperature of 30°C. Due to the burn-in a relatively constant and lower failure rate is achieved until the service life caused by wear is reached with a quality at the time of delivery that is virtually failure-free („zero defect“). Failures that may occur during the service life of the device enable fail-ures to be more easily calculated and the overall costs are reduced. |
SEPA® fans are always subject to a 3x quality inspection: • Inspection of pre-mounted assembly groups • Inspection of the installed product • Inspection after burn-in. Furthermore, at least 1% of every batch are subject to a 12500h endurance run at approx. 30°C. No more than 1% of the fans are allowed to fail after this test, usually the results are up to 3x better. SEPA® CPU coolers are equipped exclusively with ball bearing fans that are designed for operating at high temperatures. |