Base on the features and size, PLC types can be classified into following class:
• Standard,
• Mini,
• Micro,
• Pico or Nano,
• OEM,
• RTU,
• Safety,
• PAC.
Please think that trying to categorize into types of PLCs is not simply as there is a features overlapping among of them.
PLC's can be classified in many ways. Micro PLCs are tiny devices be determined to substitute a few relays. Compact PLCs are all in one units that are not expandable, but generally allow a few cards. The designs of open chassis accept extension chassis to acquire more cards. The units of modular are created from components, can have very large I/O numbers. It considers computer machine control boards, custom single board.
The DCS is at the top end they are still PLC, but the majority people don't agree. There are a lot of suppliers, each with at least one of programming language.
Some of people may recommend the Distributed Control System (DCS) is a PLC type. The DCS for process or batch and loops of PID and PLCs usually used for on and off or discrete control initially the 2 where more distinctive. Even though the PLC has developed over the years becoming very powerful controllers offered to carry out the many of the jobs that the DCS can do. You can choose to eliminate this one from category in a type of PLC, but you can definitely argue the case.
It is hard although identifying the PLCs differences in the class of Pico or Nano and the Mini and Micro. A manufacturer of PLC may define a particular line of PLC as Pico, for instance Allen Bradley, while another manufacturer will define their line of equally sized and featured model as Nano, for example GE Fanuc.
Along with types of PLC is the Remote Terminal Unit (RTU) which is particular for remote measurement of communicating and data process to a usually of SCADA systems. Since these tools may be put in the middle of nowhere they are plan to use a little power, it is possibly solar power, and continue extreme environmental. This might be quite extend if is not really controlling anything, but just conveying data measurement to a SCADA.
Safety PLCs are considered with some logic processing form redundancy and monitoring as well as self checking of input and output. As you might presumed, these charge more, approximately 30% higher than the standard cost and are apply in high risk conditions. Typically, these controllers are applied for SILs (Safety Integrity Levels) 2 and 3.
Generally, OEM PLCs are without an enclosure and hence matched to fit inside a product that is mass manufactured, for example a washing machine.
Programmable Automation Controllers (PAC) or are fundamentally the PLC tops food chain. They are very dominant in processing speed terms, programming, communications and extensibility.
Again the lines of PLC, RTU, PAC and even DCS are shaping as these once particular devices adjust more of the attributes as the others. This is easy because of the never ending technology advancement and the once expensive technology of cutting edge becoming more easily reached.
PLC Systems Types
Based on the system types following is the sample of PLCs
• Quantum, Modicon 984, 884, 584, 484, 384, 184
• Allen Bradley SLC-500, PLC-5, , PLC-3, PLC-2 PLC
• Texas Instruments 5T1/Siemens 530
• Hitachi
• Omron
• Mitsubishi
• Square D Symax
• General Electric 90/70, 90/30, Series One, Series Three, and Series Six
• Networks - Modbus, Ethernet, Data Highway Plus
• Operator Interface- Panelmate, Panelview, Dataliner.