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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.

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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 back plane. Figure 2.5 shows the standard Rackmount configuration. 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 latest systems allow the designer to integrate multiple CPU units into the hardware design of their process. This means allowing software designers (peace logic) to divide the process across multiple computing devices, making the integrity of the code more important from a security perspective. Input and Output Cards

The external information that is transferred to and from the PLC occurs on several input and output (I / O) cards. These I / O cards can contain multiple contact points, depending on user needs, and can be analog or similar with regard to the type of information sent and received. We will now give a brief overview of the input and output cards and devices they control.

Input Cards: As noted, access cards can be equipped with multiple access points, which are only in the developer’s discretion. One PLC card input generally comes with its connections points at multiples of 8, with a greater than 64 (8, 16, 24, ….. 64). PLC input cards collect their information from associated control units such as temperature sensors, level sensors, proximity keys, and VDF.

Output Cards: As with the input cards of PLC, the outputs cards can be equipped with multiple contact points. The number available in any product generally reflects those available for input cards. PLC output cards send control information in the form of analog and digital signals. These signals are used by different controllers as an activation mechanism or as a control point.

2.1.3 SCADA and Automation System Overview

PLC is the backbone of the engineering system for an industrial network. 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.

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