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DCS - Distributed Control Systems - is process oriented, while SCADA - supervisory control and data acquisition - is data acquisition oriented, DCS is process state driven, while SCADA is event driven, DCS is commonly used to handle operations on a single locale, while SCADA is preferred for applications that are spread over a wide geographic location, DCS operator stations are always connected to its I/O, while SCADA is expected to operate despite failure of field communications.
a PLC - Programmable Logic Controller - system is utilized to control a few machines in a single automation cell, while a PAC - Programmable Automation Controller - is used to control an entire factory floor via distributed I/O and command & control. There again, this will all depend on the experience of the user.
Typically PLCs have been best suited for machine control, both simple and high speed. Common characteristics of these PLCs are simple program execution scans, limited memory, and a focus on discrete I/O with on/off control.On the other hand, a PAC is geared more toward complex automation system architectures composed of a number of PC-based software applications, including HMI (human machine interface) functions, asset management, historian, advanced process control (APC), and others. A PAC is also generally a better fit for applications with extensive process control requirements, as PACs are better able to handle analog I/O and related control functions. A PAC tends to provide greater flexibility in programming, larger memory capacity, better interoperability, and more features and functions in general.
Profibus and Profinet are both field networks (i.e. communicate industrial devices with each other in the site or industrial field) so they are designed to work in industrial environment taking into account factors of dust, humidity, temperature and electromagnetic noise and interference but Profinet speed is about Mbits per second where Profibus cannot exceed Mbits per second. The maximum number of devices in Profinet network may be at least where it is for Profibus.
Profinet and Ethernet (definitely Fast Ethernet) have the same concept and wiring but profinet is industrial and more limited in length of cables ( meter for a network).
DCS vs SCADA
SCADA (Supervisory Control and Data Acquisition) is system for remote monitoring and control of process. It generally consist of large screens that make up control room from where whole process is monitored with the help of sensors and controlled with the help of controllers and actuators, any fault or breakdown can be detected using this.
DCS (Distributed Control System) is control system spread over a large area with separate controller for each process connected to one master computer which communicates with all individual controllers. The elements of DCS can be connected to SCADA for control.
PLC vs PAC
PLC (Programmable logic controller) is a computer used to automate or control the process. It consist of processor which does the computation work to generate signal on the basis of pre-programmed logic and real time input, then these signal are used to activate the actuators which finally controls the process. At a time a PLC can work with large number of inputs and outputs depending upon configuration and requirement. PLC just consist of processing unit and rest of components need to be connected seperately
PAC (Programmable logic controller) is relatively a new term which is also used to control and automate the process but unlike PLC it has all components onboard like processing unit and I/O's. It is a local control system which can be programmed using modern programming language such as C or C++. It is usually dedicated to control the I/O system and often does not provide any direct human interface.
Profibus and Profinet
Both Profibus and profinet are field communication protocols used in automation industry for communication between field devices.
Profinet uses industrial Ethernet. It is fast but can be used for short distance uptom
Profibus on other hand is old and conventional stem which is relatively slow but for larger distance it is economical.
