Hi everyone,


One of my customers has a DH+ network with several SLC 500 PLCs, several PanelView 550 terminals, and an iFIX SCADA system.


After adding a 1746-NI4 analog input module to one of the SLCs, a strange problem started: every 5–10 minutes, iFIX generates a flood of alarms from several PLCs on the network. If I remove the NI4, the problem disappears.


A few months ago, exactly the same thing happened after adding a 1746-NI8 to a different SLC 500 on the same DH+ network. Removing that module also made the problem disappear.


The alarms seem to be generated by iFIX rather than by the PLC logic. When the problem occurs, many alarms appear simultaneously, sometimes even contradictory ones. For example, the same tank can show high-level and low-level alarms at the same time.


I have already tried some troubleshooting, but so far I haven't been able to identify the cause.


Has anyone experienced anything similar with SLC 500, DH+, iFIX, or analog I/O modules?


Any suggestions about what I should check — PLC, I/O configuration, DH+ communication, RSLinx/iFIX driver, or anything else — would be greatly appreciated.

Tks,
Edson

 

Hi martigej,


HI and LO on the same tank at the same time can't be real, so I think iFIX is alarming on bad data during a comms hiccup, not on process values. Since several PLCs flood together, I'd look at DH+ before the logic.


As it happened both times after adding an analog card, I'd check the chassis power budget first, then how the analog cable shield is grounded and whether it runs near the blue hose. Also watch the iFIX driver timeouts during a flood. If they spike every 5 to 10 minutes, it's comms.


Separately, it helps to set iFIX so a comms failure shows one COMM alarm and suppresses the process alarms for those tags. Saves the operator from a pile of false alarms.


Let us know what you find.
Kiran