Essay Example on Overview of PLC Hardware

Chapter 2 2 1 2 Overview of PLC Hardware The PLC hardware can be found in two styles rack mount or block Where the major difference between them is the ability to alter the I O devices and in this chapter will give an overview of each configuration 2 1 2 1 Available Configuration Types Block configuration When the PLC is considered a block configuration the device itself comes as a standard package purchased with a predefined amount of input and output points a specific communication protocol and the CPU This configuration comes in one complete unit and cannot be changed physically The only means available to expand this configuration is by serializing the devices together using the available communication protocol and adding more blocks to the string This would allow the user to expand the number of input and output points in very small pieces Figure 2 4 shows the standard block pattern device Rack Mount Configuration Mount Rack Configuration the BlackBerry configuration allows the user to select and exchange everything in the PLC control system This includes CPU type number type of input and output cards and communication protocol Between input and output cards via a slot based structure This chassis serves dual fold purposes 1 for power supply for full rack and 2 data transfer via hardware backplane Figure 2 5 shows the standard Rack Mount configuration 2 1 2 2 PLC CPU The CPU unit of the PLC is a storage of the ladder logic program as well as the information processor collected and delivered to external devices controlled by the PLC The CPU contains all the relevant information required to fully automate the process in which it is involved Only one CPU unit is allowed in the rack configuration of the old systems currently available by all PLC manufacturers 

The information that is sent by PLC is collected for the SCADA system via input and output cards rack mount configuration or provide input and output point block configuration A SCADA computer is an information station through which the operator s control room and anyone else with intentional or unintentional access can view the real time functions of the automated system This station is generally connected over the Ethernet network to the existing network of facilities The SCADA system receives its information directly from the CPU via the Ethernet connection provider This can be in the form of a physical connection card if you are configuring a rack or internal protocol configuration block style is used Also it is now possible to share this information via wireless communication cards too which just adds another layer to the security issue The SCADA standard system in Figure 2 6 acts as a control device that is connected to one or many PLC units throughout a given infrastructure system The SCADA itself is nothing more than a standard industrial grade computer running a vendor specific piece of software which is used to watch and track the states and circumstances of each device connected to its associated control units These devices are generally calibrated with the PC system of PLC and SCADA when the initial installation is assumed to be accurate thereafter This assumption is critical to understanding the severity of the prejudice Since the control room operator studies the reliability of the data received by the PLC system and calibrates the devices using the same PLC as the calibration method any individual that access to the PLC can directly affect the system and falsify the data to the SCADA system