Chapter 8 Programmable Logic Controller Technology,8.1 Introduction,8.1.1 CPU-Central Processing Unit 8.1.2 Memory 8.1.3 Programming a PLC Controller 8.1.4 Power Supply 8.1.5 PLC Controller Inputs 8.1.6 Input Adjustment Interface 8.1.7 PLC Controller Output 8.1.8 Output Adjustment Interface 8.1.9 Extension Lines,8.1 Introduction,Fig.8-1 Basic elements of PLC controller,8.1.1 CPU-Central Processing Unit,PLC ( Programmable Logic Controller) is actually an industrial microcontroller system (in more recent times we meet processors instead of microcontrollers) where you have hardware and software specifically adapted to industrial environment. It is a device that was invented to replace the necessary sequential relay circuits for machine control.1 The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software or programmer that gives the desired results.,8.1.2 Memory,System memory (today mostly implemented in FLASH technology) is used by a PLC for an process control system. Aside from this operating system it also contains a user program translated from a ladder diagram to a binary form. FLASH memory contents can be changed only in case where user program is being changed. PLC controllers were used earlier instead of FLASH memory and have had EPROM memory instead of FLASH memory which had to be erased with UV lamp and programmed on programmers. With the use of FLASH technology this process was greatly shortened. Reprogramming a program memory is done through a serial cable in a program for application development.,8.1.3 Programming a PLC Controller,PLC controller can be reprogrammed through a computer (usual way), but also through manual programmers (consoles). This practically means that each PLC controller can programmed through a computer if you have the software needed for programming. Todays transmission computers are ideal for reprogramming a PLC controller in factory itself. This is of great importance to industry. Once the system is corrected, it is also important to read the right program into a PLC again. It is also good to check from time to time whether program in a PLC has not changed.,8.1.4 Power Supply,Electrical supply is used in bringing electrical energy to central processing unit. Most PLC controllers work either at 24V DC or 220V AC. On some PLC controllers youll find electrical supply as a separate module. Those are usually bigger PLC controllers, while small and medium series already contain the supply module. User has to determine how much current to take from I/O module to ensure that electrical supply provides appropriate amount of current.,8.1.5 PLC Controller Inputs,Intelligence of an automated system depends largely on the ability of a PLC controller to read signals from different types of sensors and input devices. Keys, keyboards and by functional switches are a basis for man versus machine relationship. On the other hand, in order to detect a working piece, view a mechanism in motion, check pressure or fluid level you need specific automatic devices such as proximity sensors, marginal switches, photoelectric sensors, level sensors, etc.,8.1.6 Input Adjustment Interface,Fig.8-2 Input adjustable interface,8.1.7 PLC Controller Output,Automated system is incomplete if it is not connected with some output devices. Some of the most frequently used devices are motors, solenoids, relays, indicators, sound signalization and similar. By starting a motor, or a relay, PLC can manage or control a simple system such as system for sorting products all the way up to complex systems such as service system for positioning head of CNC machine. Output can be of analogue or digital type. Digital output signal works as a switch and it connects and disconnects line. Analogue output is used to generate the analogue signal (ex. motor whose speed is controlled by a voltage that corresponds to a desired speed).,8.1.8 Output Adjustment Interface,Fig.8-3 Output adjustable interface,8.1.9 Extension Lines,Every PLC controller has a limited number of input/output lines. If needed this number can be increased through certain additional modules by system extension through extension lines. Each module can contain extension both of input and output lines. Also, extension modules can have inputs and outputs of a different nature from those on the PLC controller (ex. in case relay outputs are on a controller, transistor outputs can be on an extension module).,8.2 PLC Operation Process,Fig.8-4 The work process of PLC,8.3 PLC Maintenance Management,8.3.1 What Is A PLC 8.3.2 How Many PLCs Is Your Bottom Line Depending on 8.3.3 Do You Have An Up to Date List of All PLC for Your Company 8.3.4 Do You Have Trained Person Per Shift to Maintain and Troubleshoot Your Plant PLCs 8.3.5 Does Your Maintenance Work with PLCs Following Written Company Policy and Procedures,8.3.1 What Is A PLC,First, What a PLC is? As this section is not just for