Ladder Logic of Interlock Circuit

In this PLC programming for industrial automation tutorial, we will learn about PLC input devices. A logic diagram is a schematic representation of a system of interconnected components that show the input, output, and internal state of each component. The logic diagram consists of two types of symbols: • Input/Output Symbols- The input and output symbols represent the various inputs and outputs to the system. • Internal State Symbols- The internal state symbols represent the various states that a component can be in. An interlock logic diagram is a graphical representation of the relationships between input and output signals, and the states of one or more control devices. The simplest interlock logic diagram is a single input, single output, or "SISO" system. These systems are also called "2-state" systems because they can be in only one of two states: “on” or “off”. A 2-input, 2-output (or "2I/2O") system is an example of a 3-state system because it has three possible states: “on”, “off” and “unknown”. A PLC is an industrial computer system that has been designed for use in manufacturing environments. It is used to automate tasks such as machine control, sequencing, timing and data acquisition. The PLCs are often used in manufacturing plants, chemical plants, water treatment facilities and other industrial settings. The interlock ladder diagram is a type of flowchart which shows how input signals trigger output signals in a process or programmable logic controller (PLC). Inputs are represented on the left hand side of the diagram while outputs are shown on the right-hand side. An interlocking circuit in PLC is a mechanism that interprets the state of a device and controls the status of other devices. Interlocking circuits are used in PLCs to control the machine's operation. A typical interlocking circuit in PLC might have two inputs: one for an emergency stop button, and one for a "run" button. If the emergency stop button is pressed, the run button would be disabled until the emergency stop was released, so that pressing it again would not restart the machine.