First Out Indicator

This may be slightly OT. I have a printing press with approx. 200 elements in a single line E-stop loop. What will occasionally happen is when the press is running the loop will open (bad spring pressure on a stop botton, something slapping into a jam switch, etc.), causing the press to come to a grinding halt. This situation is a trouble shooting nightmare as the stop loop will reset almost immediatley. Has anyone ever come up with a scheme that will allow monitoring of the individual components of a N/C Loop, that will overcome the limitations of PLC scan time? I would appreciate any comments as the last go round started last night at 1:00am and lasted till 5:30 this morning

Regards Mike

I have worked on a system that uses an extra "hot" wire that mults through every Estop location and lights a pilot lamp thru an extra set of N/O contacts on every Estop switch (in addition to the N/C contacts that complete the Estop circuit. This will indicate WHEN an Estop switch is activated (stop),and WHICH Estop switch is activated (one pilot lamp per switch). Its a simple circuit, but adding an extra wire thru all those conduit runs and a pilot lamp at every location could be a challenge. PLC monitoring of that many individual "short term" pulse inputs will require research re operations per micro second of individual PLC brands. Maybe some of the guru's have a brand or two to suggest. I just read a little on the IDEC Pentra, much faster than it's predecessors, but I don't think it will expand to 200 inputs.

Stationmaster

Have a look at this thread

Not 100% sure if this would be a solution but Idec did do ASi based pushbuttons that have individual addresses, so monitoring would be easy. Their product was called SwitchNet.

I have their catalogue in PDF if you are interested.

Stationmaster, the Pentra will do up to 512 I/O points compared to the Microsmart at 264. To achieve this you would have to use the FC5A slim modules with expansion blocks.

Jon.

I would highly recommend the ASI interface safety system for your application. Only requires 2 wires for the complete system.


http://www.as-interface.com/safety.asp

http://www.am.pepperl-fuchs.com/pdf/documents/asi-your-safety-network.pdf