IEC 62912-2-2019 pdf free.Railway applications – Direct current signalling monostable relays Part 2: Spring type relays.
4Essential requirements of the relays and their construction
4.1Generic requirements
4.1.1Generic requirements for spring type signalling relays
The spring type signalling relays in this document shall fulfil(by themselves) all the safetyconditions for safety-related signalling systems without the aid of other relays or withoutcontrol of operations in the circuit. This kind of relay shall be compliant with the safetyrequirements specified in lEC 62425 and specifically with lEC 62425:2007,B.3.1c).
4.1.2Forcibly guided contacts
Signalling relays shall be equipped with forcibly guided (mechanically linked) contacts.Theforcibly guided (mechanically linked) contacts shall be designed in such a way that it isensured by mechanical means that make and break contacts can never be in the closedposition simultaneously.
lf one of the make contacts is closed, none of the break contacts shall be closed. lf one of thebreak contacts remains closed, none of the make contacts shall close (assuming that nominalpower 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 de-energised, 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 shallclose.(see lEC 62912:2015,5.1.1)
4.1.3Forcibly guided operation
The efficiency of forcibly guided (mechanically linked) contact operation shall be maintainedas long as the relay operates, even when beyond the specified endurance.This applies bothto loaded and unloaded contacts. Forcibly guided (mechanically linked) operation shall bemaintained even if individual parts of the relay fail.Under such circumstances, it is irrelevantwhether this failure is due to wear or breakage.
4.1.4 Degradation during service
The spring type relays shall satisfy the product specification during the service life – refer to4.7.4.
4.2 Specific requirements
4.2.1 Non-welding characteristics
The relays shall be characterised by their non-weldable make contact points, through the useof a suitable contact point material (for example，silver-carbon for which there is no risk ofwelding above a certain percentage of carbon), or by the introduction of special constructionarrangement reducing risks of welding of the contact points (for example,adequate openingforce, contacts in series, or fusing) – refer to Clause 5.
4.2.2 opening of make contactsThe relays shall open the make contacts by the force of contact springs and return springs,when the current is interrupted in the coil.IEC 62912-2 pdf download.