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IEC 62912-2 pdf free download

IEC 62912-2 pdf free download.Railway applications – Direct current signalling monostable relays – Part 2: Spring type relays.
4 Essential requirements of the relays and their construction
4.1 Generic requirements
4.1.1 Generic requirements for spring type signalling relays
The spring type signalling relays in this document shall fulfil (by themselves) all the safety conditions for safety-related signalling systems without the aid of other relays or without control of operations in the circuit. This kind of relay shall be compliant with the safety requirements specified in IEC 62425 and specifically with IEC 62425:2007, B.3.lc).
4.1.2 Forcibly guided contacts
Signalling relays shall be equipped with forcibly guided (mechanically linked) contacts. The forcibly guided (mechanically linked) contacts shall be designed in such a way that it is ensured by mechanical means that make and break contacts can never be in the closed position simultaneously.
If one of the make contacts is closed, none of the break contacts shall be closed. If one of the break contacts remains closed, none of the make contacts shall close (assuming that nominal power conditions apply — see also 4.7.2). Operation of forcibly guided (mechanically linked) contacts means that if, for example, any given make contact fails to open and the relay is deenergised, none of the break contacts shall close. The same principle applies to the failure-to- open of a break contact with energisation of the relay, i.e. in this case, no make contact shall close. (see IEC 62912:2015, 5.1.1)
4.1.3 Forcibly guided operation
The efficiency of forcibly guided (mechanically linked) contact operation shall be maintained as long as the relay operates, even when beyond the specified endurance. This applies both to loaded and unloaded contacts. Forcibly guided (mechanically linked) operation shall be maintained even if individual parts of the relay fail. Under such circumstances, it is irrelevant whether this failure is due to wear or breakage.
Use of change-over contacts is permitted for signalling relays in safety-related circuits. (see IEC 62912:2015, 5.1.2)
4.1.4 Degradation during service
The spring type relays shall satisfy the product specification during the service life — refer to
4.2 Specific requirements
4.2.1 Non-welding characteristics
The relays shall be characterised by their non-weldable make contact points, through the use of a suitable contact point material (for example, silver-carbon for which there is no risk of welding above a certain percentage of carbon), or by the introduction of special construction arrangement reducing risks of welding of the contact points (for example, adequate opening force, contacts in series, or fusing) — refer to Clause 5.
4.2.2 Opening of make contacts
The relays shall open the make contacts by the force of contact springs and return springs, when the current is interrupted in the coil.
NOTE The relays that open the make contacts by the falling of the armature under its own weight when the current is interrupted in the coil are not included in this document.IEC 62912-2 pdf free download.

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