Queuing Backwash Request

Dear All
I have got 3 water treatment plant (RO) and they require backwash.
each RO send to my PLC one DI signal to tell me that it needs backwash. My duty is getting this signal and put in sequential order (queue) and only one backwash allow at a time. when the current backwash finished the next one will start backwash. while this happening if new backwash require it will be last in the queue. If you could help that would be great.

Many Thanks in advance
sa

I am using AB SLC-500 PLC

Hi
Investigate the FIFO instruction. Which PLC are you using?

Pp

if u are using siemens simatic manager u can use the TI library
u have a table function call fc 84 which is add to table you can assign a number to each machine and add this values in the table
then use the FIFO function to see which one u should process now