What is AFI

I was asked in a interview today what is AFI I said Arc fault interrupter, but that was not the answer he wanted, It was in reference to PLC programming, does anyone have a better answer, Thanks Bill Martin

the simple answer is that AFI stands for Always False Input ...

many people (including the folks that wrote the official books) believe that the AFI will "disable" or "deactivate" a rung ... the thought is that the rung will be "skipped" and will not be executed (or otherwise acted upon) by the processor ...

that is IN-correct ... (it is wrong!) ...

actually all that the processor does is to evaluate the AFI as FALSE logic ...

so ...

be careful how you answer the question that you posted ...

the SIMPLE answer is that the AFI is just FALSE ... where you want to be careful is in going too deep – because the interviewer may not really understand the actual operation of the AFI – and might think that you've got it "wrong" – when in fact, you've got it "right" ...

take a look at this post for some more details ...

http://www.plctalk.net/qanda/showthread.php?p=337526&postcount=6

AFI is Rockwell terminology and is a ladder contact that is always false. It has a partner ladder coil NOP (No Operation) that is an always false output. To my knowledge, no other brand of PLC uses this terminology.

Him asking you that question says more about his abilities than an answer says about yours. He isn't experienced with non-Rockwell platforms and works primarily in ladder.

Thank you that helped, I have some reading to do now

Yeh,
What does the Logic do for an OTE when an open XIC or an AFI is in front of it?

Nothing Right?! Nope,

It writes a 0 into a bit box.

False. not nothing... Cool stuff on this site

Who knew PLC's were so philosophical