Working With The Safety Program; Duplicate Masters Must Be Avoided - Siemens SIMATIC S7 F Manual

Operation and Maintenance
Fiber-Optic Cables Between the Synchronization Modules in the S7-400 FH
Safety Note – Duplicate Masters must be avoided
!
In a fail-safe and fault-tolerant S7 FH System, you must prevent both CPUs from
being master at the same time, since this may result in hazardous faults.
Such a state (the two CPUs are both masters at the same time) can occur if the
two fiber-optic cables used to connect the CPUs are removed or interrupted
simultaneously when the S7-400 FH is in a redundant configuration. This must be
prevented by laying separate fiber-optic cables.
This state (two CPUs both masters at the same time) can also occur after a CPU is
repaired if the CPUs have not been connected via both fiber-optic cables before
the power supply is switched back on.
Take organizational steps to ensure that, after a CPU has been replaced, both
fiber-optic cable connections are established before the power supply is switched
on.
You can find information on replacing components in fault-tolerant systems in
manual /4/. Please refer to the references in Appendix B.)
6.3

Working with the Safety Program

You must take into account the following when working with the Safety Program:
•
You must not operate Safety Programs directly when safety mode is activated!
You can enter safety parameters:
- by means of fail-safe conversion blocks.
- in CFC test mode.
•
Access to the CPU must be protected with a password.
•
The offline project in the programming device/ES must always be kept
consistent with the CPU. In other words, no old programs, charts or blocks
should be copied to a project.
Safety Note – Safety measures must be followed
!
If you don't follow the above safety measures, this may result in errors in the
execution of the safety program and in the Safety Program Shutdown.
6-2
Fail-Safe Systems
A5E00085588-03