The modelling of the interlocking scheme can be achieved by using a chain interlocking model. This will make the model more flexible and independent of the number of used relays. Also, this chain model is more closer to reality. An example of the chain model can be found in the attachment of this FAQ. Basically, there are two models, sending and receiving models. The sending model contains two input blocks and one logic. The receiving model receives the resulting signal from sending relays and uses it to block one or more relays.