FAIL SAFE MULTIPLEXOR

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The use of  Fail safe equipment is an important requirement of equipment used for the purpose of signaling of any Transportation system specially for equipment used for the purpose of Train running. Any equipment used has to satisfy that the failure of the equipment is on the safe side and it is also highly reliable.

The design of  a safe multiplex also follows the same basic principles. This is achieved by using duplicated processors, which processes the input in two processors totally independently. The input is digital input, which in most cases is the status of a relay. This is processed by the processors, which are two in number. These processors output the information in a buffer independently. See diagram

The buffer  outputs the information on a serial channel repeating the information thrice and which is received at the receiver end buffer. The receiver-input buffer outputs the information to two independent processors. These processors check the input serial information for any transmission errors at two levels

a) By checking the errors of to two bits
b) By checking that the same information is repeated atleast twice in three consecutive packets.

The information processed independently by the two-processor output the information to a Hardware comparator and if the two outputs match then relays are picked up repeating the status of the relays at the transmitter end.

Specifications of Fail Safe multiplex

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