FEATURE SCADA & DATA ACQUISITION
PLCS AND PACS which one is right for you?
Jonathan Wilkins, marketing director of industrial obsolete parts supplier EU Automation explores the pros and cons of using traditional PLCs and newer PACs in manufacturing
B
oth PLCs and PACs are industrial computers that have been adapted for
use in manufacturing environments. These systems can control automation equipment in factories to a highly reliable degree. PLCs have been used by manufacturing industries for over 40 years while PACs are a newer addition to the automation market and generally more complex systems than PLCs. However, many industry professionals
believe that PAC is just another name for a state-of-the-art PLC because advancements in modern technology have shortened the gap between them. The biggest difference between PLCs and PACs is the way they are programmed. PACs are programmed using C and C++, making them more adaptable and efficient. On the other hand, PLCs are programmed using ladder logic — a programming language that uses symbols representing an electrical schematic of relays. This form of programming is sequential, making PLCs largely inflexible. The way the two computers are programmed creates distinct capabilities for each of them. PLCs are single microprocessor based
devices. They are typically programmed to carry out simple execution scans but they have limited memory and discrete input/ output (I/O) capacity. This makes PLCs ideal for controlling simple applications with minimal I/O requirements. PLCs should be used for basic control schemes where complex analogue control and motion control are not necessary. In other words, there is no need to pay a higher price for a PAC if the application does not require a higher level of functionality.
COMMUNICATING WITH SCADA SYSTEMS However, PLCs are being developed to have more functions. Modern PLCs have built in networks which enable them to be used to communicate with other PLCs as well as human machine interfaces (HMIs) and supervisory control and data acquisition (SCADA) systems. A PLC might be enough to fulfil all a plant manager’s automation needs. PACs are the equivalent of an extra
caffeine injection because they normally use two or more processors. In this sense,
26 FEBRUARY/MARCH 2018 | IRISH MANUFACTURING
using a PAC could be likened to using a PC and a PLC together. PACs are made up of various computer based applications, making them more flexible to program. Unlike PLCs, they can multitask easily by operating in multiple domains such as motion, discrete and process control.
INTEROPERABLE PACS
PACs are used because of their interoperability. They are optimal for large
CYBER SECURITY EVENT IN CORK
Leading industrial software provider SolutionsPT, together with Schneider Electric, is hosting an OT cyber security event on 15 March 2018 at Fota Island Resort, Cork, aimed at helping manufacturers protect their industrial control systems and critical infrastructure. Keynote speaker Jay Abdallah, global security director at
Schneider Electric, will discuss The Threat Within, covering how the move to open standards such as Ethernet, TCP/IP and web technologies has allowed hackers to take advantage of industrial control systems and critical infrastructure, before moving on to Defence in Depth. The afternoon session will give attendees the opportunity to take part in workshops, covering Wonderware System Platform 2017, SolutionsPT’s responsive control platform for SCADA, MES and IIoT solutions, before concluding with optional Citect SCADA and ThinManager hands-on workshops.
PACS and PLCs have a time and a place that suits them best. However, that doesn’t mean you can have one but not the other
applications but can be scaled down for use on smaller ones. Their modular design makes them useful in simplifying expansion processes, as adding or removing components is easy to execute. Their compatibility with other
components allows PACs to communicate with other PLCs and higher level computing systems such as manufacturing execution (MES) and enterprise resource planning (ERP). Programmers are starting to push PACs one step further by integrating third party applications and real-time control. Companies may soon be able to run PC applications such as Windows in real-time. This maximises flexibility as well as offering integration of control and information. Using PACs alongside other networks can improve the efficiency of the business as whole. Just as we might crave an espresso when we wake up but opt for a cup of tea for an afternoon pick-me-up, PACS and PLCs have a time and a place that suits them best. However, that doesn’t mean we can have one but not the other.
EU Automation T: 0845 521 3088
www.euautomation.com
CONNECTINGINDUSTRY / IRISHMANUFACTURING
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