What can I say? I love relay logic because there are only 2 possible outcomes in every decision tree. The answer is either yes or no, and that is it! This is also called Boolean logic which is basically the same type used to design gate configurations in digital logic circuits. (Something else I know how to do) I got introduced to relay logic when I worked at S&S Machinery. I started out there rewiring imported machine tools for resale in the USA. After a while I became so familiar with relay circuits you could just tell me what you wanted the machine to do and I would design the circuit straight out of my head and build it. You can go the Machine Tool Section of this site and look at some of the circuits and machines I rebuilt when I worked there. My first relay system was for an old used cylindrical grinder. My last relay circuit there was for a brand new 35 ton 6 axis 3 head vertical boring mill that was coming in from China without electrics. On this machine they gave me the original schematics from China, which showed they used 218 relays to achieve all the functions with fixed speed AC motors.
The schematic was too complicated to understand. I threw it in the garbage and asked my bosses for a verbal description of what the machine does. From that I designed a complete control system that used 4 variable speed drives and only 67 relays to do the job. I left the company a year or so later, but I heard the Chinese had bought the machine back to analyze how I could make it work with all variable speed motors using 75% less components than they did in the original design.
In the photo above are relay panels I mass produced in house while working at Union Standard for a big order they had gotten for FA1 package wrapping machines. These panels controlled the main motor, temperatures of the heater systems, and the paper feed registration drive. Click on the tab for Flow Wrappers to view the slide show on this project.