There are 2 types of PLC systems to consider when choosing the correct PLC. Unitary (brick) A unitary PLC is a contains a basic system in one compact unit. The features include a main module which contains a CPU, the input and output modules and a power supply. They are usually fitted directly to the component or machine that needs to be controlled. Unitary PLC’S are usually used for any application that doesn’t require a lot of inputs/outputs. For example, a sensor on a conveyor belt, it would only require a simple program and would not use many inputs/outputs. There are several advantages to using a rack mounted PLC: They are small and compact, so they can be used in places with very little room or for smaller processes. They hold all the …show more content…
They are very simple and basic; therefore, they are not suitable for a large-scale process. Rack Mounted The modules of a rack mounted PLC are on standard cards which slot together into a rack inside a control cabinet. The rack is used for the modules to communicate. Advantages They can be modified and expanded which allows a lot of flexibility for the application of the PLC. They have the most Input/Output points out of all the types of PLC’s If a feature fails unlike a unitary PLC where the whole unit must be replaced only the part that failed has to be changed in a rack mounted PLC which saves money. Disadvantages They can take up a lot of room depending on the process they are used for. They are usually the most expensive of the PLC types. These PLC’s are mainly used in the manufacturing industry. This is mainly because of the number of I/O points that the system can contain as there are a lot of large scale process in manufacturing industries and its ability to communicate with other networks. PLC selection criteria consists of: …show more content…
it must perform the function needed to meet the requirements of the job it’s designed to be used for. For example, if a PLC is t used in a fast-moving large-scale process you would want a PLC with a fast CPU and a large number of inputs/outputs. Communication and compatibility If the application of the PLC requires it to share data outside of the process it needs to be able to communicate with another electronic device such as a computer. It is important to know whether your desired PLC is compatible with other electronic devices and programs used by those devices. Environment Will the environment in which the PLC and process be operating experience extremes of temperature, dust or humidity? To ensure the reliability of the PLC it must be kept in an area within its specified environmental conditions range. For example, a PLC used in a work area that uses water for most of its processes it must have an IP rating of IP65 Enclosure so its protected against water projections from a nozzle as an example. Different IP ratings give a lot of information on the intended environment of the