PLC's - Programmable Logic Computers

There are three types of PLC’s which can be used for many applications

·         these are Unitary

·         Modular

·         and Rack Mounted PLC’s.

The reason there are three types of PLC’s is because that some are better suited to use in various applications.

When selecting a PLC for an application there are a number of factors to consider. Such as memory size, speed of operation, cost, compatibility.

 An good application for a Modular PLC would be theme park rides. This PLC is more suited to this application as a Modular PLC can be built up and changed over time as the park or application changes. This type of PLC is quite expensive, but this is because the number of input/outputs can be changed to suit the application. Also adding more inputs/outputs on this type of PLC is easier as more modules can be added to the PLC. Maintenace in modular PLC’s is easier because if one module goes faulty, this is the only component that needs to be replaced unlike with Unitary PLC which would all need to be replaced. This PLC can also be networked so that they can all be monitored from one location, although unitary PLC’s can also be networked with a added on section.

Unitary PLC’s could be suited for many things, just one of these is a lighting system such as in a factory or warehouse. This is because a lighting system requires less inputs and outputs. The size of the program is relatively small, therefore the cost of a Unitary PLC is greatly cheaper than a Modular PLC which is an important factor as each system would have its own PLC. Also a Unitary PLC takes up much less room than a modular PLC so installation is easier, although both pof these are rack mounted its not really a major issue in most applications although modular are seen as the more durable of the two.

An ideal application for a Rack Mounted PLC would be in car manufacturing. This PLC would be best used in this environment as it uses both Modular and Unitary PLC’s, so you have advantages of both PLC’s and you have the ability to communicate more with other netoworks. This is useful as this type of application requires various programs to operate multiple tasks, which in a car factory are quite considerable as there are many factors of production in producing one car. Rack Mounted are probably the most expensive PLC but they do have the advantages of both types of PLC’s at hand. This means that this one Rack Mounted PLC can run an entire operation line in the factory, from maintenance to operation, so if effiency is more important than the over all initial investment then rack mounted are a suitible choice.