help understanding fifo allen bradley

Hi guys
Can any one help me understand how a fifo works ,and how you program please, its for improving my knowledge thanks stu

Here are a couple of threads, and there are probably some others that would help.

http://www.plctalk.net/qanda/showthread.php?t=18344

http://www.plctalk.net/qanda/showthread.php?t=65614&highlight=FFU/FFL

First In First Out

means this:

instruction 1, instruction 2, instruction 3 --> order of execution: 1, 2, 3

LIFO on the other hand would have order of instruction: 3, 2, 1

FIFO is like a queue - who entered first will be processed first

Expanding on Stu's question ... does anyone have a control example where a LIFO was appropriate?

stacks are using lifo

I used a LIFO on a vessel that was filled + extracted from the bottom. The control system had to monitor each tanker that was offloaded into the storage vessel (which had the capacity to store about 5 tankers worth). Each offload had to register an entry into the LIFO with the current level of the tank and the eventual end level once the offload had finished. I then used this information to remove the entry from the LIFO, once the tank level had fallen to the value contained within each LIFO entry. I also had to store a lot number for product traceability purposes, which forced me to build my own block attaching x number of datawords to each LIFO entry.

Thanks for your replys , has anyone got any examples of a working fifo thanks

Hi Stu,
See these two threads for working examples
http://www.plctalk.net/qanda/showthread.php?t=75912

http://www.plctalk.net/qanda/showthread.php?t=51896

Hope it's helpful

Best regards,
Donnacha

check out this link. it is the one i started a year ago. it includes zipped programs.

http://www.plctalk.net/qanda/showthread.php?t=65565


regards,
james

FIFO Demonstration for RSLogix500 (using LogixPro)

Stu, Here is a short RSLogix500 FIFO Load and Unload demonstration (written in LogixPro simulator). You will see that it unloads to Output O:2 in the same order as it loaded (Binary 0 to 100). As the FFU Position indicator (R6:2) counts down from 100 to 0, the Output goes from 0 to 100.