Programmable logic controllers (PLCs) are available from a wide range of vendors and from PLC center. PLCs are well-adapted to a range of automation tasks. It was a need in the US automotive industry that called for the need of PLCs to replace old school relay systems. The tasks that PLCs generally perform are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. Before purchasing a PLC it is advised to do some research on PLC center and acquire an understanding of the service that they offer.
A Programmable Logic Controller (PLC Center)
Programmable logic controller units contain input and output devices compatible with industrial pilot devices and controls. Little electrical design is required, and the design problem centers on expressing the desired sequence of operations. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a “generic” solution, and where the non-recurring engineering charges are spread over thousands or millions of units.
- When choosing to purchase from PLC center, there will be a choice between a used PLC and a new PLC.
- These days, with everybody trying to minimize their carbon footprint, there is heavy pressure on industry to recycle old equipment.
- By purchasing a used PLC, you continue the process and ensure that old PLCs are not disposed of unnecessarily.
- There is also the choice of different sizes of PLCs that will be available at PLC center.
Programmable Logic Relays
There are small products called PLRs (programmable logic relays), which are more widely accepted. They are very similar to PLCs and are used in light industry where only a few points of Input/output are involved, and low cost is desired. These small devices are typically made in a common physical size and shape by several manufacturers, and branded by the makers of larger PLCs to fill out their low end product range. Popular names include mini PLC, NANO PLC, and other names implying very small controllers. Unlike regular PLCs that are usually modular and greatly expandable, the PLRs are usually not modular or expandable, but their price can be two orders of magnitude less than a PLC and they still offer robust design and deterministic execution of the logic.
The Benefits Of The PLC Center
The range of PLCs from tiny to large, new and used will be available from PLC center. PLC center will also carry out PLC repair, which means that when the PLC malfunctions it may not be necessary to buy a new one, but rather take it in for a repair. By repairing, you save yourself money and look after the environment.
In this economic climate where saving money is very important, many people are turning to PLC repair (programmable logic controller repair) to mend their old PLCs that have malfunctioned instead of spending money on an entirely new piece of equipment. PLC repair is a common endeavour these days and there are many vendors available that can help you out, but as always it is very important to research your vendor before you approach them to ensure they are reputable and known in the industry as a company that does a good job.
- PLC repair is far cheaper than purchasing an entirely new piece of equipment and repair parts are widely available.
- It is recommended that you research your PLC brand and check which a PLC center they direct you to.
- PLC’s are complex pieces of machinery and it is important to take very good care of them.
- They have progressed considerably in the past 40 years.
PLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations. Once the PLC is programmed, it doesn’t need to be fiddled with again – for that reason many people opt for PLC repair, as it means they get to retain the machine that they has already been programmed.
PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a “generic” solution, and where the non-recurring engineering charges are spread over thousands or millions of units. The high cost PLC and PLC applications once again demonstrate why PLC repair is widely preferred to buying an entirely new piece of equipment.
Choose A Reputable Vendor For Repairs
- Because PLCs are complex pieces of equipment, it is advised that you get your PLC repair work done through a reputable vendor. With repair work in the majority of cases you can expect to have your repaired equipment back within three weeks and longer repairs are mainly due to the delivery time for components.
- If your PLC is damaged or malfunctioning it is cheaper to undergo PLC repair than to replace the PLC. Repairs are generally 15% – 50 % of the cost to purchase new and can in most cases be done within a month and more often than not a 2 day priority repair service is available for emergencies.
The Programmable Logic Controller Unit Is Hardier Than PCs
The programmable logic controller unit (or PLC unit) will generally consist of the following separate elements:
- a power supply
- controller and relay units for input and output
A programmable logic controller is very similar to a normal PC computer, however, there are some key differences. A programmable logic controller unit is different from an average desktop computer because it is armoured for severe conditions and thus well suited to be used in an industrial environment – where the conditions are far harsher than in the average office or home space.
A PLC Unit Is More Durable
- A programmable logic controller unit is made resilient enough to stand up to severe conditions including excessive dust, moisture, heat and cold.
- They also, unlike normal PCs, have been designed to handle extensive input and output (also known as I/O) arrangements. These connect the PLC to sensors and actuators.
- PLCs read limit switches, analogue process variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision.
- On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analogue outputs.
- The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.
The programs of a PLC unit are written individually on personal computers before being transferred or downloaded directly over a network to the PLC. Plc software makes this possible. There are typically two types of storage that can then be used with the programmable logic controller unit. The individually written program can either be stored in battery backed up RAM or another hard drive or back up disk or flash memory stick – all dependent on preference. The PLC became popular because one PLC can be programmed to replace thousands of relays. The positives of that are endless, but mainly the PLC became popular because it decreased costs and time spent doing the yearly update on the relays – a process that would take a very long time as the mechanics had to reprogram each relay individually. With the PLC it is one program.
Ladder Logic Diagram Programming
Initially most PLCs used the same programming technique, known commonly as: Ladder Logic Diagram Programming. This sort of PLC programming was modeled on electromechanical control panel devices (such as the contact and coils of relays) which PLCs replaced.
IEC 61131-3 currently defines five programming languages for programmable control systems:
- FBD (Function block diagram)
- LD (Ladder diagram)
- ST (Structured text, similar to the Pascal programming language)
- IL (Instruction list, similar to assembly language)
- SFC (Sequential function chart)
These techniques emphasize logical organization of operations.
While the basic concepts and theories utilised in PLC programming are to be found in all products at all manufacturers, there are a variety of smaller differences in I/O addressing, memory organization and instruction set that will mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different programmable logic controller units may not be directly compatible.
A Miniature programmable logic controller – known as a mini PLC for the purpose of this article – is a miniature version of the regular programmable logic controller (PLC). The PLC, which was designed in the 1960s in order to fulfil a need that arose in the US automation industry, is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. A mini PLC is a smaller version that is used in smaller industries that is less complex to learn about.
SR Intelligent Controller
An example of a mini PLC is the SR intelligent controller, which is a type of programmable controller programmed by FBD. ” … it is simpler and easier to learn than the conventional PLC. Combining with voice module and remote control module, it can perform telephone remote controlling, wireless controlling, voice prompting and auto-dialling functions. Being used with expansion module, the input/output points can be expanded to satisfy your requirements.” From the description it can be surmised than mini programmable logic controller units do the same job as normal PLCs, just on a smaller scale. Another, probably more well known example of the mini PLC would be the 1772-LZP SER A MINI-PLC-2/02 PROCESSOR from Alan Bradley.
In automation, there is no standard for communication today. Even though the basic PLC principles used by each manufacturer are the same – the small differences in products means that most PLCs are not automatically compatible.
- PLCs have built in communications ports, usually 9-pin RS-232, but optionally EIA-485 or Ethernet.
- Modbus, BACnet or DF1 is more often than not included as one of the communications protocols.
- Other options include various field buses such as DeviceNet or Profibus.
- These differences often make PLC repair a very specialized field, as not all PLC’s can be repaired by any one given PLC center.
Each manufacturer uses its own protocol. An example of these sorts of differences can be shown by Ethernet PLCs EtherNet / IP (Ethernet Industrial Protocol) which is an open communication protocol developed by Rockwell Automation. It is managed by ODVA and designed for use in process control and other industrial automation applications. EtherNet / IP can be easily confused with a combination of Ethernet (physical layer, link or medium used in most office environments and many industrial networks) and Internet Protocol, the world’s most widely used (Internet) protocol network and some TCP / IP model, which includes a suite of protocols that operate on the link, the Internet (or network), transport and application layers.
PLCs may need to interact with people for the purpose of configuration, alarm reporting or everyday control.
- A Human-Machine Interface (HMI) is employed for this purpose.
- HMIs are also referred to as MMIs (Man Machine Interface)
- and GUI (Graphical User Interface)
A simple system, which is more likely to be found in a mini PLC, may use buttons and lights to interact with the user. Text displays are available as well as graphical touch screens. More complex systems use a programming and monitoring software installed on a computer, with the PLC connected via a communication interface.