We are getting random serial link Fault in Preferred Rack of LM. When checked on system it shows only link fault with 11 strobes on RCM. No SIOM appears as OFFLINE SIOM.

The fault appears even when the preferred rack is in Secondary status.
After resetting the power of rack the processor comes to OK state normally getting Link fault cleared, but sometimes ACTV LED of Port A on all the SIOM remains OFF.

We have replaced almost all the modules in preferred processor rack.
Checked the end terminations at SLM and last SIOM, those are OK.
Anybody have faced same type of problem and got it resolved permanently.

pl. reply.

 

Random Serial Link Failures are often caused by:
1. Grounding issues

2. Floating logic issues in the serial port (basically, not all the pins are connected, and the system interprets it as undetermined)

3. Misconfigured baud rate, parity, etc.

Is this a problem with new equipment, or did you recently upgrade certain pieces of the system? Are you using any Ethernet to Serial converters? Is the failing serial interface attached to a PC, another PLC, a touchscreen, or a card within the same rack?

Mike

 

Try end termination resistances in SIOM. They should be placed in physically the last IO rack.

Also check which SIOM goes in fault when SLM announces link fault.

 

Thanks for your reply.

Already replaced the term resistors in last SIOM rack.

No SIOM shows fault when there is link fault, in this case, that's why it is confusing !!!

 

Some clarity required here

1. When the fault appears, the processor swap-over occurs. Did you try resetting the fault by shorting pin 18-19 on SLM?

2. In case of SLM link fault, the link which this SLM was serving (either SLINK A or SLINK B) should have gone inactive. Which link goes inactive? Does it come back active after reset pulse on pin 18-19 of SLM?

3. When this preferred pri. rack is secondary, even then SLINK fault occurs. So does, this cause all the ACTV LED on all SIOM of either A or B go off?

 

Thanks SPR for your continued help.
Answer to your queries are

> 1. When the fault appears, the processor swap-over occurs. Did you try resetting the fault by shorting pin 18-19 on SLM?

Ans : When the preferred rack is primary and fault occurs, processor gets swapover. The fault has occurred even if the preferred rack is in Secondary. There is no such problem observed with the Non-preferred rack. I always do power recycle to reset the fault.

>2. In case of SLM link fault, the link which this SLM was serving (either SLINK A or SLINK B) should have gone inactive. Which link goes inactive? Does it come back active after reset pulse on pin 18-19 of SLM?

Ans : Here only one link is there (I mean only one SLM is there). As fault comes in preferred rack, only PORT A link gets ceased. Normally the link comes back in active after resetting. But sometimes it comes to active after 4-5 retries.

>3. When this preferred pri. rack is secondary, even then SLINK fault occurs. So does, this cause all the ACTV LED on all SIOM of either A or B go off?

Ans : Yes. When this preferred pri. rack is secondary, SLINK fault occurs even then also. This cause all the ACTV LED of port A on all SIOM to go off.