Electromechanical Relay Logic

The following schematic is of a relay circuit that emulates a standard digital logic gate function:

Write a truth table for this circuit’s function, and determine what name best represents it (AND, OR, NAND, NOR, or NOT).

The following schematic is of a relay circuit that emulates a standard digital logic gate function:

Write a truth table for this circuit’s function, and determine what name best represents it (AND, OR, NAND, NOR, or NOT).

A type of electrical diagram convention optimal for representing electromechanical relay circuits is the ladder logic diagram. An example of a “ladder logic” diagram is shown here:

Each parallel circuit branch is represented as its own horizontal “rung” between the two vertical “rails” of the ladder. As you may have noticed, some of the symbols resemble standard electrical/electronic schematic symbols (toggle switches, for instance), while others are unique to ladder logic diagrams (heater elements, solenoid coils, lamps).

Where do the circuits shown obtain their electrical power? What do “L1” and “L2” represent? How are relay coils and contacts represented in a ladder logic diagram? Answer each of these questions by expanding upon the diagram shown above: draw the components necessary to show a complete electrical circuit (i.e. details of the power source), as well as an additional rung (or two) showing a relay coil actuated by some sort of switch contact, and the relay contact controlling power to a second indicator lamp.