Logic Analysis

Thread Starter


Joined Jan 8, 2016
Hello everybody, small homework problems, namely, I do not understand what K1 means on this picture.
As far as I understand I1.0, I1.1 and I1.3 and inputs, but I have absolutely no clue what K1 boxxed and K1 switched means. Could anyone help me on this one. Is K1 boxxed supposed to be I1.0 AND I1.1 placed to be in the place of K1, making Q1=(I1.0*I1.1)'+I1.3 ???
* is AND
' is NOT
+ is OR

Mod note: reduced image file size


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Joined Feb 24, 2006
It is called a ladder logic diagram.

The box labeled K1 is a relay coil or maybe some similar type of device. The coil is energized (conducts current) when both switches I1.0 AND I1.1 are closed. Think of the top horizontal line as having some voltage on it and the bottom horizontal line as being the ground return. I don't know for sure but the line labeled K1 is one of the set of contacts associated with relay coil K1. What I don't know is if those are the normally open contacts or the normally closed contacts. You will have to consult your own reference materials to resolve this ambiguity on my part. I1.3 is also a switch of some kind and again it is different in some fundamental way from switches I1.0 and I1.1. Again you may have to do some research to find out what the symbol means. The logic for Q1, and again I'm not familiar with the symbol, is that Q1 is "energized" if either K1 OR I1.3 is conducting current.

Each of the pathways from top to bottom is another "rung" on the ladder. In a ladder everything happens in PARALLEL.


Joined Aug 1, 2013
I would assume that switch K1 as shown is the normally closed contact set for relay K1, and state that assumption as part of my answer.