-QNAN on Inputs


I am using a SNAP-OAC-EB2 with 12 analog input modules in a 16 slot rack. Each of the input modules has 8 analog inputs. I am measuring temperature with this system.

Every once in a while (about 1-2 times per week), all of the inputs into one module will produce a “-QNAN” for about 2 to 3 minutes, then resume working correctly. This has occurred on several different modules. Whenever it happens, it affects all 8 inputs into the module.

Anyone have any clues as to what might be causing this?

The SNAP system is connected to a Controllogix PLC with an ethernet connection through a Stratix 8000 switch with an expansion module (18 ports in total). The PLC and the switch are working normally.


Hello Kurt9,

Welcome to the forums!

Often that’s due to too-low voltage on the rack. Check out [U][B]this video (click here) [/B][/U] for how to check that. In the video, Ben also mentions [U][B][URL=“http://www.opto22.com/site/documents/doc_drilldown.aspx?aid=1789”]this doc[/B][/U].

Do the occurrences of this problem correlate to other machinery coming on? Does it tend to happen more on modules furthest from the PAC on the rack?

Also don’t forget that [U][B]Product Support is FREE[/B][/U]! if you’re still having trouble.