This chapter discusses:
Hthe normal operation of a Hot Standby CPU Redundancy PLC system;
Hwhat happens when a fault is detected and the system does not operate normally;
Hhow to restore the system to normal operation;
Hon-line repair procedures.
Section 1 describes normal system operation of a Series 90-70 Hot Standby CPU Redundancy system, Section 2 describes what happens when a system failure is detected, the actions taken by the system in response to detected faults and how to restore the system to normal operation.
Section 5: System Operation
Power-Up Sequence of a Redundant CPU
When a CPU is powered up, it will perform a complete hardware diagnostic check and a complete check of the user program and configuration parameters. This will cause the power up time of a redundant CPU to be significantly longer than the normal power up time of a simplex (non-redundant) Series 90-70 CPU. If the Primary and Secondary systems are powering up together each CPU must recognize this fact so that the Primary system will become the active and the Secondary system the backup.
The following sequence outlines each step in the power-up process. The only difference in this sequence as compared to the power-up sequence of existing CPUs is that full power-up tests are always performed instead of conditionally depending on whether STOP mode is selected, and the detection of the other CPU along with initialization of each RCM followed by synchronization.
1.Power-up self-test is performed.
2.CPU operating system is initialized and PLC memory is validated.
3.Diagnostics called for ºFullº power-up tests performed.