Compact Logix 1769-L32 Network Status(NS) LED Flashing

Dear all,

I am new to the PLC world. Compact Logix PLC is programmed to read ricelake weigh Scales (Gross/Net/Tare) and DCS will read weight from the PLC.

There are 3 PLC's configured to read weights. Each PLC communicates with 7 Ricelake weigh scale through Ethernet/IP CIP protocol. Each ricelake weigh system will have its unique IP address. 2 Message block is used to read weight value and write command(Return Gross, Net, Tare etc..).

All 3 PLC's have exact identical program only difference is IP address for weigh scales communicating to each PLC. PLC1 and PLC3 is working fine reading weight and it send write command as well.

PLC2 working for a while then it lost its communication with weigh scales and DCS. So i did the power reset again PLC2 working for some time and it looses its communication i checked the LED light NS(network status) flashing green... PLC1 and PLC3 NS LED light is solid green. So i double checked my program everything looks OK... I configured overhead time slice as (90%).

Can anyone help me what causing the PLC2 looses its CIP connection after some time ????

I appreciate all your help

I had a very similar problem with one of my plc here where I work. After a great deal of searching and hair loss I found that my boss who was working on a spread sheet had inadvertantly turned the polling frequency in the odb/dde server to 1 MS. This burden on the network keep causing my MSG statements to die. I would look at the load on your ethiernet, the frequency of MSG statements and any settings on your scales. Compare your other plc's that are working fine to the one that is not working well.

#1) Bad Cable. Self-crimped Ethernet ends.
#2) Bad Switch (Ethernet)
#3) Bad Power (noisy)
#4) Someone powering up a device with a duplicate IP.
#5) Something is set to fixed speed/duplex, instead of being pure, 100% AutoNegotiate.
#6) Heat.
#7) Bad PLC.

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90% overhead time slice? Good Lord. I only run 30, on very large systems, talking to multiple HMI's and other PLC's.

my guess - it is possible you are trying to get the data too quickly.

use a cyclic timer to intiate your messages, poll your weighscales at a rate that is appropriate, not at PLC scan cycle rates.

remember you are probably sharing the ethernet bandwidth with many devices, including your own programming PC, or the weighscales themselves can't service the requests at the frequency you are sending them.