devicenet inputs being maintained in program

hey everyone, long time since my last post.

my issue is we have a bank of valves on devicenet with a controllogix controller. when we have a device failure like no comms, bus off, etc the inputs in the logic are maintained at their last state. for example, a valve is closed and making the closed prox and this prox input is true in the program. if you unhook the cable going to the valve, the input stays true in the program. the DV scanner of course displays node# and e78, but the input stays true in the logic therefor not faulting and alarming the valve on our scada.

I think this is a parameter on each device in the dnet program. maybe parameter 2 and/or 3?? I'm not sure though. can someone help me out?

thanks!!!

Welcome back to the Forum !

What you describe is normal operation for a DeviceNet system (and really, for most PLC I/O systems I'm familiar with).

Input data always stays at the last value before the connection was interrupted, so that the control system at least knows what the value *was* previous to the connection failure. If it set the value to zero on connection failure, you would lose that critical bit of data.

I've seen some programmers who make their networked I/O more DCS-like by changing every boolean value into an integer: "0" is BAD, "1" is FALSE", and "2" is TRUE.

I just use the connection failure diagnostic data when I need to take action based on a disconnected sensor. Most DeviceNet scanners have a 64-bit connection status table, and the modern ControlLogix/CompactLogix ones have a table of integer values that give the connection status or status code (like the 72/78 you see when a device gets disconnected).

Most DeviceNet output devices can be configured for how you want them to take action when the network connection is interrupted (or when the PLC goes to PROG mode), but the state of the input data in the controller's Input data table is the DeviceNet Scanner module's decision, and it always holds the last state.

thanks Ken! let me digest that and work on it.