Do you mean a "/" to indicate a NC contact? No, not necessarily. It depends on the physical level sensor contacts, whether they are open or closed at any specified liquid level. We are told that the sensors are both Normally Closed on-the-shelf (not immersed in liquid). Therefore, Sensor 000 will be closed with an empty tank. To make the pump come on at the empty level, and then run until the High level is reached, all PLC instructions should appear as shown. At mid-level, the pump will be running, unless the PLC program is not started until the tank is at that level. If the program is started with the tank already at mid-level, the pump will not run until the level drops to Low.
This logic relay duplicates or simulates a physical relay, which has both a coil and 1 or more contacts (switches). In the diagram, "1000" with a circle under is the symbol for internal PLC relay coil number 1000, and 1000 with "| |" underneath is the symbol for a contact operated by relay coil 1000. I only see ONE copy of the internal relay "1000", not two copies as you assumed.
Thanks to Mrs Butler, my high school Business Admin teacher. Then the electric typewriters were the wave of the future, and we thought we were working in "high cotton". I started the Gregg Shorthand course under Mrs. Butler also, but could not take the stress of being in a class with 30 girls. They would forget there was one guy in there and let their skirts (all skirts, no pants allowed) creep up during class (or so they said).
