Programmable Logic Controllers - Coursework Example

Programmable Logic Controllers Name Course Tutor Date Contents Abstract Festo PLC Stations Cross referencing Scanning process and Batch I/O Update Emergency Stop function Abstract Programmable Logic Controllers are state of the art digital computers especially designed to handle automated and specialized electromechanical processes. PLCs are specially designed to handle simultaneously multiple outputs and inputs. The function of the Sorting Station is to arrange work pieces into three designated slides. There is a diffuse sensor on the sorting station whose function is to detect the work pieces on the conveyer. Work piece features are detected by upstream sensors located above the stoppers. There is a retro-reflective sensor whose function is to monitor the level of all three slides. The Sorting Station has a CP valve terminal alongside a DP slave commonly known as a Profibus-DP interface. The station has plug connectors for connecting the sensors to the valve terminal’s input module. The Profibus-DP valve terminal is required for the station to operate effectively. The purpose of this study is to program the station so that it follows a designated pattern, which will be discussed as the study unfolds. Festo PLC Stations In the automation lab, the following stations are supplied; Sorting Station, Separating Station, Handling Station, Processing Station, Pick Station, Buffering Station, Place Station, Fluidic Station, Testing Stations, Muscle Press Station, Place Station, Punching Station, Distributing Station and the Assembly Station. A total of 11 PLC stations assembled by the Festo Company are supplied in the automation lab. Table 3 Sorting Station Mapped Profibus and Directly Connected Addresses Sorting Station I/O Type Name Profibus Address Bit No. Mapped Address Inputs Part On Conveyor 1 0 I 2.0 Reflective Part 1 2 I 2.2 Metallic Part 1 1 I 2.1 Part on Shute 1 3 I 2.3 Shute 1 Eject 1 5 I 2.5 Shute 1 Not Eject 1 4 I 2.4 Shute 2 Eject 1 7 I 2.7 Shute 2 Not Eject 1 6 I 2.6 Start Direct 0 I 125.0 Stop Direct 1 I 125.1 Reset Direct 3 I 125.3 Auto Manual Switch Direct 2 I 125.2 Outputs Conveyor Motor 1 5 Q 3.5 Part Stop Back 1 4 Q 2.4 Shute 1 Eject 1 0 Q 2.0 Shute 2 Eject 1 2 Q 2.2 Start Button Indicator Direct 0 Q 125.0 Reset Indicator Direct 1 Q 125.1 Q1 Indicator Direct 2 Q 125.2 Q2 Indicator Direct 3 Q 125.3 In reference to Table 3, the first step to ensure that when the start button is pushed, the conveyor starts is to ensure that the Profibus Address (Bit no. is 0) or Auto Manual (bit no. is 2)switch is direct. This way, the input path will automatically set Sorting Station immediately you press the start button. In the output segment, you ought to set the Profibus Address on the conveyer motor at 1 and the bit number at 5 in order to ensure that when a part is detected on the conveyor, it stops at the Part Stop and is assessed whether it is metallic or plastic. The conveyer motor will automatically detect whether the part is metallic or plastic. To ensure that the part is allowed through the stop, the Profibus Address on the stop ought to be direct with the bit number being 1 as illustrated in the table. In case the part is metallic, for Shute 1 Eject to send it down to Shute 1, the Profibus Address should be 1 without any number of bits as shown in the output part of Table 3. To ensure that if the part is plastic, Shute 2 Eject sends it down Shute 2, the Profibus Address on Shute 2 Eject must be 1 double the bit number i.e. 2. In order to ensure that the sorting system is capable of sorting multiple parts, there are a variety of considerations. First, there must be a diffuse sensor on the sorting station whose function is to detect the work pieces on the conveyer. Likewise, ensure that work piece features are detected by upstream sensors located above the stoppers. Thirdly, the station must have a retro-reflective sensor whose function is to monitor the level of all three slides. Also make sure that the Sorting Station has a CP valve terminal alongside a DP slave commonly known as a Profibus-DP interface. The station must also have plug connectors for connecting the sensors to the valve terminal’s input module. The Profibus-DP valve terminal is required for the station to operate effectively. The essence of all the above is to ensure that the system is capable of sorting multiple parts. To ensure that the sorting system automatically stops when 10 of any part has been through it, the Profibus Address on the Reset Indicator must be in ‘direct’ mode with the bit number being 1. Pressing Stop at any time will stop the system provided that the Profibus Address on the Stop button is on ‘direct’ mode. Cross referencing Cross referencing, as used in this context, refers to using sorted, real time information in an attempt to eliminate errors and produce an error free schematic diagram. By simply clicking on a symbol – as shown in the diagram above - you should know the number of contacts assigned to relay and the exact place they are located. Scanning process and Batch I/O Update The technology behind internal hardware architecture is quite similar to that of other microcontroller based systems bearing digital and analog I/O, ROM, RAM and communications links. They have a supple (modular) configuration such that when you plug in appropriate modules, it is possible to configure I/O in a way that suits the task. As the task changes, it becomes easy to reconfigure the system. In case of difficult and protracted tasks, it is less likely to monitor ad infinitum, rather than sequentially, contingent upon the model of the software. Is it possible to run concurrent processes, or must they be sequential? This depends on the software model and how the tasks are to be performed. There is a loop whose function is to monitor timers, software flags, events and readings. The program also carries out tasks as detected after which it returns to the loop. The program ought not to spend too much time on one task otherwise there is a technicality. The limit of the design could be a few seconds for any given task in the loop. The time taken to detect an event varies significantly depending on the nature of the task. When the process is too slow, it is advisable to refer individual tasks to different PLCs with the network. Such transference allows better concurrency since there are lesser tasks for each PLC; each PLC can specialize in the task at hand. Research and explain why an Emergency Stop function cannot be connected to an ordinary PLC system, Discuss options for implementing an emergency system. First, it is important to note that Siemens produces PLCs that are safety rated. As such, the PLCs can form part of a safety system. Likewise, ordinary PLCs have the functioning capacity either from the core or as part of emergency shutdown systems. Nonetheless, this needs numerous design efforts and as such, it makes it impossible for a number of applications. It is important to refrain from using a non safety rated PLC when operating under safety shutdown systems. In the United Kingdom, they have 5 performance levels (a, b, c, d and e) for safety shutdown. E is the highest level. The level to use depends on the danger that the machine is likely to apprehend considering the injuries likely to be sustained by operators or other personnel. Level d is safe for regular PLCs so far as operators have accurate information to compute the reliability. Likewise, it is important to take necessary steps not to tamper with the code. You must implement error checking mechanisms as well. Profibus and Fieldbus As an acronym denoting Process Field Bus, Profibus is a unique field bus system. Profibus is the number one Fieldbus system used to facilitate communication in automation technology with over 30 million installed nodes making it the world’s leading fieldbus system in the global market. In order to enhance the capability of automated communication, Siemens has a wide range of comprehensive portfolio of systems and products. The growth of Profibus is unprecedented. Standardized as IEC 61158, Fieldbus is the name given to the group of industrial computer network protocols. Fieldbus is a complex automated system used for real-time distributed control. Some of the advantages of Fieldbus are that there is an interface – Human Machine Interface – at the top of the hierarchy of controller systems that aids the operator to monitor the system while operating it. The interface helps the system to function. Fieldbus is globally acclaimed and is used in all production and processes. Likewise, uniform Profibus solutions significantly reduce maintenance cost thus boosting productivity. Despite the highlighted cost advantage, there are major setbacks associated with Fieldbus. For instance, the systems are quite complex which calls for highly qualified operators. Likewise, the components of Fieldbus systems are very expensive with a longer reaction time. OSI model The OSI – Open Systems Interconnection – Model standardizes and characterizes the purpose of communication systems by grouping similar communication functions into logical layers. OSI model standardizes and characterizes such functions in terms of abstraction layers Reference Bolton, W. Programmable Logic Controllers, Fifth Edition, New Jersey: Newnes 2009 Read More