Photoeye signal output in industrial enviroment

Hi all, this is my first post, I just got a gradute job, but there was one question at the interview I could not answer, I am curious to know if someone has the answer.

It was about how would we know that the output from a photoeye sensor is 100% correct in an industrial enviroment with many noises and similar? The field the interview was for is PLC.

Thanks

plc-girl said:

Hi all, this is my first post, I just got a gradute job, but there was one question at the interview I could not answer, I am curious to know if someone has the answer.

It was about how would we know that the output from a photoeye sensor is 100% correct in an industrial enviroment with many noises and similar? The field the interview was for is PLC.

Thanks

Click to expand...

Trick question.
Some special sensors have built-in "sensor checking circuitry".
If not, you need to consider the nature of "the output".
If it is digital, then it really only has two outputs, TRUE or FALSE.
But, the questions sounds more like it is probing about the photoeye aspect than the signal aspect.
Hmmmmm.
My quess is that the question was written by someone who never used a photoeye, much less ever set one up.
Perhaps a tricky answer would be :
Install two sensors: one LIGHT operated, one DARK operated.
But, even with that, you have "The man with two watches".