Watchdog card internal to the processing unit

Each processing unit has a watchdog card that ensures the fallback position of the unit. The card communicates with the CPU card through a bus backplane (mixed ISA and PCI bus). The internal counter is periodically reset by applying the CPU card. 

The principle of the card is to measure a predetermined dynamic processing of the CPU unit and to generate a negative power supply (diode pump) to activate the polarized relay located on the card. 

This card is designed so that no single failure  

This relay is similar to those in the output cards. It is periodically self-tested. Self-testing of this relay ensures its availability to solicitation. 

The period of self-test is justified by a classical probabilistic approach But the frequency must not render the electrical contact of the relay unreliable by excessive solicitation, so a period of less than 10 minutes is chosen. 

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