Writing Resources
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
