We're having intermittent cable faults on our LCN. The system has been checked from top to bottom. Fiber has less than 2db of signal loss (checked using HW procedure), although it is long run (close to max. distance). LCNE boards have been replaced, grounding checked, LCN cables replaced, terminators checked or replaced, ext. LCN has been physically isolated and terminated with just a couple of nodes and still had B cable problems. Faults normally start on B cable but have began showing up on A. Can someone explain why breaking the B cable connection at the home end would clear errors (temporarily)? System has run for hours or days before faulting??? Any wisdom would be appreciated.

 

We had a similar intermittent fault we couldn't identify, eventually determined to be two bad LCN-I/O cards and one bad LCNE card. We replaced all LCN parts at the distant site (4 nodes), which cleared the problem, then re-installed old cards one at a time to ID the bad parts.

 

another couple of things for consideration from the school of hard earned lessons learned. The LCNEs have a tight DC voltage spec and do not like ripple. We had a case where 1 of the 2 redundant supplies were turned off. The other supply was weak and caused errors. Eventually the noise increased to point where we saw errors even with both supplies on. The honeywell manual discusses the DC voltage spec, but I don't think we saw the ripple issue talked about. You don't note the age of your system, but there is a customer resource document that cautions on older power supplies.

Your note comments "FAULTS". Are you getting to a cable suspect or bad condition. You say you have been top to bottom so you may have checked this already, but looking at the errors may point at a specific node or communication direction. If the problem is a node, you may only see a problem when certain data is asked from certain nodes.

Last we recently installed a new LCNE. The ex-Honeywell engineer that was overseeing the job took great pains to balance the fibers making sure that they were the same length. As you talk long length that is one more thing to think about if you have exhausted everything else.

good luck.

 

Another couple of things to check. You do not mention the power supplies on the LCNEs or whether this is new or old installation. We had 2 issues over a couple of years relating to power supplies. The LCNE needs clean DC power. The manuals mention this, but they do not mention to look out for a ripple voltage. There is a separate service note for that. It does not take much and they have improved the newer supplies (powered by own cord).

Another thing to check. Don't know if certain nodes are showing errors from other nodes. Patterns may point at a problem node. You probably already looked at this. Good Luck

 

Faults from cable B showing up at cable A. Have you checked for crossed cables?