# Electromechanical relay logic

Posted on Feb 4, 2014

In ladder logic symbolism, an electromechanical relay coil is shown as a circle, and the contact(s) actuated by the coil as two parallel lines, almost like a capacitor symbol. Given this knowledge, interpret the following ladder logic diagram: How do we know which relay contact is actuated by which relay coil How does this convention differ fromthat of standard electrical/electronic schematic

diagrams, where the relay coil is shown as an actual coil of wire (inductor symbol) with the contact "linked" to the coil by a dashed line Also, what type of logic function behavior (AND, OR, NAND, or NOR) does the above circuit exhibit In ladder logic diagrams, relay coils are associated with their respective contacts by name rather than by proximity. In this particular circuit, the logic function represented is the AND function. Many students find it confusing that relay contacts and coils need not be drawn next to one another in a ladder logic diagram, because it is so different from the schematic diagrams they are accustomed to. The non-necessity of proximity in a ladder logic diagram does have its advantages, though! It is simply a matter of getting used to a new way of drawing things. There is a problem somewhere in this relay logic circuit. Lamp 2 operates exactly as it should, but lamp 1 never turns on. Identify all possible failures in the circuit that could cause this problem, and then explain how you would troubleshoot the problem as efficiently as possible (taking the least amount of electrical measurements to identify the specific problem). This is a problem worthy of a good in-class discussion with your peers! Of course, several things could be wrong in this circuit to cause lamp 1 to never energize. When you explain what measurements you would take in isolating the problem, be sure to describe whether or not...

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