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PowerPoint® Presentation Chapter 4 PLC Hardware PLC Development • Programmable Logic Controllers • PLC Sections • PLC Input Sections • PLC Output Sections • PLC Power Supplies • PLC Central Processing Units • PLC Programming Devices • PLC Classifications • Form Factors • PLC Memory • Random Access Memory (RAM) • Electrically Erasable Programmable Read-Only Memory (EEPROM) • PLC Operating Cycle Chapter 4 — PLC Hardware PLCs require less space and are easier to modify than hardwired control components. Chapter 4 — PLC Hardware Regardless of the form factor, all PLCs have five common sections. These sections are the input section, output section, power supply, central processing unit (CPU), and programming device or port. Chapter 4 — PLC Hardware PLC input sections have LEDs that indicate when an input device is sending a signal to a specific address of the input section. Chapter 4 — PLC Hardware The internal circuitry of a PLC input section converts signals to the voltage level required by the CPU, and the internal circuitry of an output section converts signals from the CPU to the voltage level required by output devices. Chapter 4 — PLC Hardware PLC output sections have LEDs that indicate when the CPU sends a signal to a specific address of the output section to turn ON an output component. Chapter 4 — PLC Hardware Power supplies convert the supplied voltage to a voltage level the CPU and other electronic circuits can use. Chapter 4 — PLC Hardware The CPU compares input signals to the stored PLC program in order to turn output components ON and OFF. Chapter 4 — PLC Hardware Integrated programming devices provide a convenient way to access a PLC program without additional hardware; however, making any programming changes with an integrated keypad can be time-consuming. Chapter 4 — PLC Hardware Handheld programming devices can copy, store, and transfer PLC programs to multiple PLCs that have the same type of programming; however, viewing and editing programs is still limited. Chapter 4 — PLC Hardware Operator interface panels allow access to PLC programs and operation similar to PC access but with slightly limited capabilities. Chapter 4 — PLC Hardware PCs are the most common programming devices used with PLCs but require specific interface cables and connectors specific to a PLC family and manufacturer. Chapter 4 — PLC Hardware The size of a PLC is determined by the number of input and output terminals on the PLC. Chapter 4 — PLC Hardware Typically, fixed PLCs are used in small applications that require only a couple of sensors or switches, and where space is limited. Chapter 4 — PLC Hardware Modular PLCs are made up of individual sections that can be added to a PLC to expand the PLC’s I/O and power capabilities for almost any application. Chapter 4 — PLC Hardware Memory in a PLC is used for program files that contain the user PLC program and data table files, which contain the status of inputs and outputs, timer preset and accumulated values, counter preset and accumulated values, and other program instruction values. Chapter 4 — PLC Hardware The standard unit of memory for a PLC is the 16-bit word. A bit is the smallest unit of memory. Chapter 4 — PLC Hardware The operating cycle of a PLC runs continuously and sequentially while data tables are updated as inputs and outputs change state.