SN 29500

The MTBF calculation standard Siemens SN 29500 comes from Siemens, and is also maintained and updated by them.
To put it simply, Siemens SN 29500 is a ready-to-use IEC 61709, which also comes from Siemens.

- Rather engineering-heavy. Formula work is obviously not based exclusively on field data.
- Siemens SN 29500 is considered by TÜV as the holy grail  
- Often used for MTBF calculation
- Siemens SN 29500 is mostly used in the area of functional safety in German-speaking countries, even before the much better known Mil-HDBK-217. (The reason is simply that MIL-HDBK-217 is rather unknown at TÜV).

A disadvantage in comparison to all other MTBF calculation standards is that Siemens SN 29500 consists of 12 individual documents, each of which follows its own revision status and in some cases differs considerably in terms of calendar topicality. As of 2015, the current editions of the 12 individual documents range from 2004 to 2011.

With regard to electromechanical component types, i.e. switches, relays, contactors and connectors, it is the most detailed and mature standard. Overall, however, the Siemens SN 29500 must be described as rather basic. It does not quite reach the coverage quality of other standards and knows only one environmental condition, which on top of that is not explicitly described. From practical experience, it can be said that these must be average industrial environmental conditions.

The unique selling point of Siemens SN 29500 is the much more specific classifications regarding ICs compared to other standards. Siemens SN 29500 differentiates for linear ICs, for example, between operational amplifiers, switching power supplies, voltage regulators, etc.

Within the German-speaking area, with the exception of military and aerospace areas, the Siemens SN 29500 is almost always a good choice. Globally, the Siemens SN 29500 is also still somewhat common.