s7400H diagnostic

Hello mansourkh;

What exactly do you mean when you say the S7-400H "releases" its fiber-optic connections? The fiber-optic links between the CPUs can become faulty, and need to be replaced, or one of the CPUs can become damaged or present a fault that shuts it down. 

These cases are shown in the following diagrams, taken from the S7-400H manual.

SIMATIC Fault-tolerant systems S7-400H (V6.0)

https://support.industry.siemens.com/cs/us/en/view/82478488

In such a case there will be active LEDs on the CPUs, either Redundancy (for the fiber-optic link ;loss) of Busfx or SF for the faulty CPU. You should always start by opening the diagnostic buffer of the faulty CPU to see what messages are logged; this generally will also give you a description of the probable cause of your problem. Read the manual (section 11.3 mainly) to see how to diagnose the problem.

In a Y-link, the IM 153-2 redundant interface modules will hold the diagnostics for the underlying Profibus slaves. See our friend fritz's reply to this thread for suggestions on how to read the diagnostics from the Y-Link.

Giagnostic for Y-link and DP-slaves after him

https://support.industry.siemens.com/tf//us/en/posts/giagnostic-for-y-link-and-dp-slaves-after-him/90012/?page=0&pageSize=10

Hope this helps,

Daniel Chartier

Hello mansourkh;

Just to make things clear for everyone here:

- you have a S7-400H system with 2 running CPUs, no active LEDs on the front of the CPUs, no problem controlling your process.

- you pull one of the fiber-optic redundancy links out of one of the CPUs, expecting the system to fail, but it continues running.

- when the fiber-optic lead is disconnected, there are no Redundancy LEDs lighting up on the CPUs (or any other diagnostic LED), and no further entries appear in the diagnostic buffer related to that issue.

Is this a correct description of your situation?

Hope this helps,

Daniel Chartier