Three Parameters controlling single output

[strebej]

I really need some help on this one.  I have three Oxygen / Combustables analyzers.  Each one is set up to close a descrete dry contact when an alarm (High / Low Set Point) has been reached.  I will progam the PLC to show the alarm status of each independent analyzer.  The process is to have the three analyzers online at the same time.  There is a main fuel trip (MFT) that will trip the boiler if more than ONE analyzer goes into an alarm status.  The problem is I need to design a Logic diagram and produce a generic program, (PLC model not important).  This program will need to be able to allow any one of the three analyzers to go into an alarm status and still remain online (No MFT).  but! if any one of the other two goes into alarm then set the MFT.  I will also need to be able to take any one of the three offline for maintainance.  In this case then both of the other analyzers will need to have an alarm before a MFT is activated.  Do you see my delema.  

[support]

If you use the T100MD888+ PLC TBASIC language you can accomplish this quite easily by counting the number of ON alarm status. If more than 1 alarm comes on, (doesn't matter if it is 2 or 3), it will activate the MFT.

E.g.   Assume the 3 alarm connects to inputs #1 to #3:

N = 0             ' N is the counter for number of alarm
FOR I = 0 TO 2
   IF  TESTBIT(INPUT[1],I)
       N = N+1       ' increment alarm count
   ENDIF
NEXT

IF N < 2          ' 0 or 1 alarm
    RETURN      ' do nothing.
ELSE
     SETIO  MFT   ' activate MFT
ENDIF

That's all.