scope:

This part of IEC 61810 covers test conditions and provisions for the evaluation of endurance tests using appropriate statistical methods to obtain reliability characteristics for relays.

This document applies to electromechanical elementary relays considered as non-repaired items (i.e. items which are not repaired after failure).

The lifetime of a relay is usually expressed in number of cycles (CTF). Therefore, whenever the terms "time" or "duration" are used in IEC 61649, they carry the meaning "cycles". However, with a given frequency of operation, the number of cycles can be transformed into respective times (e.g. times to failure (TTF)).

The failure criteria and the resulting characteristics of elementary relays describing their reliability in normal use are specified in this document. A relay failure occurs when the specified failure criteria are met.

As the failure rate for elementary relays cannot be considered as constant, particularly due to wear-out mechanisms, the cycles to failure of tested items typically show a Weibull distribution. This document provides numerical and graphical methods to calculate approximate values for the two-parameter Weibull distribution, as well as lower confidence limits and a method for confirmation of reliability values with the WeiBayes method.

This document does not cover procedures for electromechanical elementary relays where enhanced requirements for the verification of reliability apply.

NOTE 1 Such reliability test procedures are specified in IEC 61810-2-1. In particular, when electromechanical elementary relays are intended to be incorporated in safety-related control systems of machinery in accordance with IEC 62061 and ISO 13849-1, IEC 61810-2-1 defines procedures for the manufacturer to provide B10D values.

NOTE 2 Electromechanical elementary relays with forcibly guided (mechanically linked) contacts according to IEC 61810-3 offer the possibility of a high diagnostic coverage according to 4.5.3 of ISO 13849-1:2015.