RELAY LOGIC DIAGRAM SYMBOLS
Electromechanical Relay Logic | Digital Circuits Worksheets
wwwboutcircuits›Worksheets›Digital CircuitsElectromechanical Relay Logic representing electromechanical relay circuits is the ladder logic diagram. to the relay coil and contact symbols.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.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 you are actuating either of the pushbutton switches when you take those measurements.The wiring sequence shown here is not the only valid solution to this problem!Pushbutton switch A fails open: Lamp 1 always energized, lamp 2 simply becomes inverse status of pushbutton switch B. Relay coil CR2 fails open: Both lamp 1 and lamp 2 simply become inverse status of pushbutton switch A. Relay contact CR1-1 fails open: Lamp 1 simply becomes same status as pushbutton switch B. Relay contact CR2-1 fails shorted: Lamp 1 always energized. Relay contact CR2-2 fails shorted: Lamp 2 simply becomes inverse status of pushbutton switch A.Like semiconductor gates, electromechanical relays have but two states: energized and de-energized (1 and 0). Like gates, the contacts of relays may be interconnected to perform standard logic functions such as AND, OR, NAND, NOR, and NOT.This is an AND function.This is an OR function.This is just one example of how the ladder logic diagram could be expanded: “L1” and “L2” represent the “hot” and “neutral” lines, respectively, in a 120 volt AC power system. Often, the control circuit power is obtained from a step-down transformer, which is in turn fed by a higher voltage source (usually one phase of a 480 volt AC three-phase system, in American industrial applications).Never, ever connect load devices in series in a control circuit such as this!If you thought that the “faulted” truth table would be all 0’s, you probably thought I said relay contact CR2 failed open. The fault I proposed was relay CR2 coil failed open.
Ladder Logic Symbols - All PLC Diagram Symbols
Ladder logic symbols are a set of symbols used in PLC ladder diagrams. Download all the IEC 61131-3 ladder diagram symbols as DWG, PDF and PNG files here.