Unitary PLC, Rack-Mounted PLC and Modular PLC

Unitary PLC, Rack-Mounted PLC and Modular PLC Overview Before PLCs were created many industries such as the automobile industry used hundreds of thousands of relays to control their processes. This was very time consuming and expensive, sometimes resulting in a two year change around between different products because electricians would have had to individually rewire every relay to change a production system for a different line of cars etc. Programmable Logic Controllers or PLCs were first designed in 1968 when General Motors decided that a replacement for this type of process was needed. PLCs are designed for multiple inputs and outputs. A PLC is essentially a small computer which is used for mainly industrial purposes but also has other uses. Industrial uses could be: Packaging lines Robots Hydraulic machines Pneumatic machines Other uses could be; Traffic lights Car parking barriers Signalling systems PLC Units There are three types of programmable logic controllers (PLCs). They are Unitary, Modular and Rack mounted. All three types have different features both good and bad which make each type suitable for many different applications. Unitary PLC Design and characteristics A Unitary PLC contains all the features of a basic system in one compact unit, the features include; A power supply. The main module which contains a central processing unit (CPU). The input module. The output module. Unitary PLCs are fitted directly to the component or machine that they are controlling. The advantages of a unitary PLC: They are small and compact. They hold all the basic components in one unit. They allow portable and easy access. They are usually the cheapest type of PLC. The disadvantages of a unitary PLC: They cannot be expanded. If any feature fails then the whole unit has to be replaced. They are very simple and basic. Applications Unitary PLCs can be used for any application that does not require a lot of inputs or outputs. For example a car park barrier, this would not use many inputs/ outputs and would only require a simple program. Modular PLC Design and Characteristics Modular PLCs are a system of modules that can be slotted together to build up a system. The basic modules contain; A power supply. The main module which contains a central processing unit (CPU). The input module. The output module. Other types of module can be attached as well as extra input and output modules to increase the capacity or to cope with changes in hardware system. The advantages of a modular PLC: The amount of input and output terminals can be expanded to cope with any changes to the hardware system. If any feature fails then only that part has to be changed saving on cost. The disadvantages of a modular PLC: They are expensive compared to unitary PLCs. Applications Modular PLCs are useful for applications where there would be a lot of inputs and outputs because more input/output modules can be added if needed. This type of PLC is widely used in the manufacturing industry to control process lines. Rack-Mounted PLC Design and Characteristics The design and characteristics of a rack mounted system are very similar to a modular system however these modules are on standard cards which then slot together into a rack inside a control cabinet. These modules communicate via the rack. The advantages of a rack-mounted PLC: They are easily modified or expanded. They have more I/O points than any other type of PLC. If any feature fails then only that part has to be changed saving on cost. The disadvantages of a rack-mounted PLC: They are usually the most expensive of the three PLCs Applications Like the modular PLC this type of system is widely used in the manufacturing industry. This is mainly because of the amount of input/output points that the system can contain but also because it has the ability to communicate with other networks. Internal Workings of a PLC CPU The CPU- Central Processing Unit acts as the brain of the PLC. It contains a memory unit into which the PLC program is written into. It is basically used to process the information it receives from inputs and carries out instructions to the outputs according to the logic programmed into it. This process is called the scan cycle and it occurs every 5ms. The scan cycle is shown below. (Ref 2) When a program is written on a programming device such as a laptop it is uploaded to the CPU, once it has been uploaded it is then written into the CPUs memory. The programming device can then be disconnected without losing any data from the PLC because the program is now saved into the memory of the CPU. Only the unitary PLC has a CPU built into it, on the modular and rack-mounted PLCs the CPU comes as a separate module. On modular PLCs the CPU would be the first module whereas on rack-mounted PLCs the CPU is governed by the amount of inputs and outputs that are being used. Input and Output Devices In PLCs data is collected from inputs which are connected to the input modules and sent to the CPU, this data is then executed within the program logic and then sent to the output devices via the output modules to perform a specific task. The inputs and outputs are assigned a reference point in the PLC so that they are easily recognisable when programming. An input device is any peripheral piece of hardware that is used to send data information and control signals to any information processing system, in this case the PLC. In terms of PLCs there are two different types of inputs, analogue and digital. An example of an analogue input would be a sensor or transmitter and an example of a digital input would be a switch, push button etc. Inductive proximity sensor An inductive proximity sensor will detect metal surfaces or devices without coming into contact with them. The sensor face is made up of windings from the oscillator. These form an alternating magnetic field around the sensor face called an inductance loop. The inductance of a loop will change if a metal is placed inside it because metals are much more effective inductors than other types of material. Once the inductance loop is altered the change is detected by sensing circuitry which then signals to another device such as a PLC. Capacitive sensor A capacitive sensor will detect any surface or device without coming into contact with it. A capacitive sensor uses an alternating voltage which in turn causes the positions of the charges to continually reverse. This then creates an alternating electric current which is detected by the sensor face. The sensor face is made up of capacitors from the oscillator. The amount of current flow is determined by the capacitance, and the capacitance is determined by the area and proximity of the conductive objects. Therefore the larger and closer the object then the greater the current will be and vice versa. Photo Electric Sensor A photoelectric sensor uses light to operate. When a preset level of light is picked up by the sensor the sensor switches. This type of sensor is used to detect moving objects, for example bottles on a conveyor are detected due to the bottles breaking the line of light. Once the line has been broken the switch signal is fed into the electrical control circuit which provides a corrective action. There are three types of photo electric sensor. These are Reflective, retro-reflective and separate type. Optical Reflective Sensor The light is reflected off the surface of the bottle back to the receiver. Optical Retro-reflective Sensor The light is transmitted and reflects off a reflective surface back to the receiver. Optical Separate Sensor Outputs An output device is basically any device that is controlled via the output module of a PLC. In terms of PLCs there are two different types of outputs, analogue and digital. Analogue devices are devices that the output can be varied. Digital outputs are used to control two state devices, this means that they are either on or off. An example of an analogue output would be motor speed; valve position etc and an example of a digital output would be a relay, solenoid valve etc. Indicators Indicator light The simplest of the PLC outputs, the indicator light simply shows that a certain function has worked correctly, for example if a machine was in run mode then a green indicator light could also be activated to notify operators etc that the machine is running. Indicator buzzer Acts in the same principle as the light but uses sound; it is more effective at alerting someone to a problem especially if that person does not have a line of sight of the machine. For example if there was an error that has caused a machine to stop then the buzzer would sound. Solenoid valve A solenoid valve can be operated electrically and pneumatically. In the case of a normally open 3/2 valve it uses one of these to switch it from off to on. Solenoids are named after the amount of states or ports they have and also what function they do. For example a 3/2 spring return solenoid has 3 ports, 2 states and once it has been deactivated it returns back to its natural position via a spring. The 3/2 valve below is shown in two stages. Stage 1 is where the valve is in its natural state where air is flowing from P (the air supply) to b (the exhaust). Whereas in stage 2 the valve is activated allowing air to flow from P to a where the air is sent to another device for example a cylinder. Stage 1 (Ref 1) Stage 2 (Ref 2) Signalling Signalling refers to the use of signals for controlling communications. Signals can be either digital or analogue. With digital signals the signal is logic therefore it is either a 1 (True) or a 0 (False). With analogue signals the entity is continuous where the signal is constantly varying based on real time. For example the amount of light a sensor receives is an analogue signal because it can be any value within the range that the sensor can pick up. (Ref 1) In some systems both digital and analogue signalling is needed. For example a house phone shares the same network connection as a pc. In this case a device called a modem is used to convert the signal between the two. (Ref 2)http://geekrich.com/wp-content/uploads/2011/09/home-network-diagram.gif Networks A PLC must communicate with other devices in order to operate. These devices are connected to the PLC via a network. There are many different types of network such as: Bus Network A bus network is a long cable acting as a backbone which links devices together, the backbone has nodes connected to it via a single line. The signal travels in both directions until they are terminated at either end. The amount of nodes that can be attached however is limited to the strength of the signal. http://www.olson-technology.com/mr_fiber/images/bus_network.gif (Ref 1) LAN- Local Area Network A LAN network is used to connect different hosts in a small area such as an office or a small building. Data is sent in the form of a data packet which includes the address of both the sender and the destination. http://berbagisolusi.files.wordpress.com/2011/12/lanwan11.gif (Ref 1) Programming There are three main types of programming that are used in PLCs. These are; Ladder logic Structured text Functional block Ladder logic Ladder logic is one of the most common styles of PLC programming and it is used in most manufacturing companies. It is called ladder logic simply because the style resembles a ladder as shown below where the two vertical rails are connected by a rung. Rung Rails (Ref 1) It is popular because of its similarity to relay logic which in turn allows most program designers to easily grasp the concept. Ladder logic is written using logic symbols which are shown below and is read from left to right. Ladder logic symbols (Ref 1) Normally open Normally closed Normally open immediate Normally closed immediate NOT Positive transition Negative transition Output Output immediate Set Set immediate Reset Reset immediate Set-dominate bistable Reset-dominate bistable No operation Example of Ladder logic Below is a simple circuit designed to mimic a drilling process where 3 cylinders are used to drill a part. Cylinder a when extended places a part below cylinder b, whilst cylinder c is already extended holding the part securely in place and also preventing the part from falling through the gap below cylinder b. Cylinder b then comes down, drills the part, goes back up and cylinder c retracts allowing the part to fall through the gap. (Ref 1) Cylinder B Cylinder A Cylinder C The ladder diagram for this circuit is shown below. (Ref 1) As can be seen from above the system uses sensors to show whether each cylinder is extended or retracted. This information is then used to activate each cylinder. For example in the first part of the programme which has been highlighted; Relay R1 is activated when the start button is pressed given that the stop button is in the normally closed position. Sensor 5 (S5) is off which is showing that cylinder 3 is extended. When this is off it allows Relay 1 to stay permanently on because one of the contacts from R1 can then complete the circuit and create a latch. R1 is then used to activate solenoid 1(Sol1) to extend cylinder 1 provided that S2 and R4 are off. Structured text Structured text is a text based language that uses statements to define what needs to be executed. Structured text uses statements such as: IF†¦THEN†¦ CASE†¦OF†¦ FOR†¦DO†¦ WHILE†¦DO†¦ REPEAT†¦UNTIL†¦ People who are trained in computer language find structured text easier to understand than ladder logic because they are of a similar format.

Relation of Crime and Family Essays -- Sociology Essays Papers Crimina

Crime is sometimes blamed on the family, with poor parenting, lack of discipline and family breakdown often associated with youth crime. A recurrent theme in academic research has been to investigate the relationship between delinquency and a range of family related factors. Early studies explored child-rearing behaviour, parental discipline, the criminal histories of parents and family size and income. Popular theories in the 1950s and 1960s related juvenile delinquency to material deprivation, broken homes and to the growing number of ‘latch key’ children who were left unsupervised after school while their mothers went to work. All of these presaged current concerns with discipline and the role of single-parent families. What has emerged from this research is that some family factors are related to the likelihood of delinquency but that they must be considered in the context of the socio-economic circumstances of the family and the others factors such as school and the peer group. The following factors have emerged as particularly important. Parental discipline and supervision Parental discipline has always been seen as a major factor underlying youth crime and it was found that inconsistent and erratic discipline are more likely to be associated with delinquency than lax or strict discipline (West and Farrington 1973, 1977). More recent studies have focused on the quality of parental supervision, often measured by whether parents know where their children are when they are not at home. A Home Office study in 1995, for example, found that supervision was strongly related to offending with higher numbers of those who were no... ...ng number of people who are able to work but choose not to, live in a ‘different world’ from others. They do not obtain good habits and discipline and their values contaminate ‘the life of entire neighbourhoods’ (Murray 1996:p123). Men in such communities cannot support families, leading to high rates of illegitimacy, and seek alternative, destructive means of proving that they are men. Whole communities are devastated by crime and young men look up to criminal role models. Whether or not the underclass exists, most agree that industrial restructuring has led to the growth of communities within which the majority of inhabitants are excluded from work and its associated benefits, and that these are also characterised by high amounts of property crime, youth crime and illegal drug use (Davies, Croall & Tyrer 1999).

Why and How Have Liberals Supported the Fragmentation

Why and how have liberals supported the fragmentation of political power? (15) Why Liberals are concerned about power, most basically, because power constitutes a threat to liberty. Their concern about concentrations of power is rooted in their emphasis upon individualism and its implication that human beings are rationally self- interested creatures. Egoism determines that those who have the ability to influence behaviour of others are inevitably inclined to use that ability for their own benefit and therefore at the expense of others.The greater the concentration of power, the greater will be the scope of rulers to pursue self-interest and, thus, the greater corruption. Lord Acton stated â€Å"Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men. † behind Acton’s famous quote about power and corruption, he points out the liberal belief that, since human beings are individuals and therefore egoistical, they are bound to us e power – the ability to influence the behaviour of others to benefit themselves and they will use, or abuse, others in the furtherance of that goal.In essence, the greater the power the greater the scope for using and abusing others in the pursuit of self-seeking ends. Such thinking has shaped liberalism in a number of ways. In particular it has encouraged them to endorse the principle of limited government brought through constitutionalism and democracy. Liberals thus support, for example, codified constitutions, bills of rights, the separation of powers, federalism or devolution, as well as regular, free and fair elections, party competition and universal suffrage. Constitutionalism delivers limited government either by legally ring-fencing government (e. . , codified constitutions and bills of rights or fragmenting government power so creating a network of checks and balances (e. g. , the separation of powers, bicameralism and federalism). Democracy delivers limited gover nment because it bases government on a system of popular consent and accountably that also enables the public (through competitive elections) to rid themselves of unpopular or corrupt governments. The fragmentation of power brings many significant benefits. It creates a network of checks and a balance, ensuring that power is a check on power.Different bodies and institutions will eventually act as a check on each other. Fragmented government therefore creates internal constraints that prevent government from becoming a tyranny against the individual. Furthermore, it ensures that those who exercise power have only a limited ability to influence other citizens, thus preventing absolute power. How Traditionally, liberals have always supported fragmented government, checks and balances. Power within liberal democracies is separated between the legislature, executive and judiciary which act as both independent and inter-dependent bodies.The separation of powers emphasises it cuts on powe r into smaller pieces – thus preventing concentrations of power from developing – and that it creates internal tensions amongst institutions and power-holders which further diminishes the capacity of each to abuse or tyrannise the general public. Liberals support constitutionalism and consent because they fear that government may become a tyranny against the individual, based on the assumption that power is inherently corrupting and concentrations of power will lead to absolute corruption.This assumption is rooted in the liberal view of human nature: as individualism implies self- interest, those with power over others are apt to abuse it for their benefit and at the expense of others. Constitutionalism is the theory or practice of restricting government power through the establishment of a framework of constitutional regulations, usually involving the fragmentation of power to create a network of checks and balances. Liberal constitutionalism is expressed through supp ort for various external and internal devices, such as codified constitutions, bills of rights, the separation of powers, federalism or devolution, and so on.Liberal support for consent is evident in support for electoral democracy in general and, more specifically, sympathy for referendums and proportional representation. Consent is the principle that the right to govern derives from the willing agreement of the governed, who thus view the actions of government as rightful or legitimate. Consent is often in practice associated with the act of voting and therefore institutionalised through a system of electoral democracy. Liberals emphasise the importance of constitutionalism and onsent because both are mechanisms for protecting or enlarging the sphere of individual liberty by restricting the capacity of government to encroach upon the individual. This commitment to limiting government reflects the underlying liberal fear that power is inherently corrupting, a consequence of egoism, meaning that government is always liable to become a tyranny against the individual. Constitutionalism achieved this aim through formal, institutional and often legal restrictions upon government officials and bodies.Consent achieves it by ensuring that politicians are publicly accountable and, ultimately, removable. ? Federalism, based on the principle of shared sovereignty, devolution, parliamentary government, cabinet government and so on. ? Power is devolved from the centre to regions and at local levels. In the UK: regional assemblies- welsh assembly; Scottish parliament ? Human rights act: giving people rights in law which means that they have a check to defend themselves from being discriminated against by those in authority

Cleaning Staff ESL Dialogue

​​Jared knocks quietly on the door in response to Ms. Andersons request. He offers help and provides some information about the services offered at the hotel.   Jared: (knocks on the room door) May I come in, madam? Ms. Anderson: Yes, thanks for coming so quickly. Jared: Certainly, madam. How can I help you? Ms. Anderson: Id like some fresh towels in the suite when I get back this evening. Jared: Ill get them immediately. Would you like me to also change the bed sheets? Ms. Anderson: Yes, that would be nice. Could you also turn down the covers? Jared: Is there anything else I can do for you? Perhaps you have some laundry I can take to be cleaned. Ms. Anderson: Now that you mention it, I do have some clothes in the laundry bag. Jared: Very good, madam. Ill have them cleaned and folded when you return. Ms. Anderson: Excellent. You know, it gets stuffy in this room. Jared: Id be happy to open the window while you are away. Ill make sure to close it before you return. Ms. Anderson: †¦ oh, I can never find the light switch when I get back in the evening. Jared: Ill make sure to leave the lamp on the bedside table  on after I finish cleaning up. Ms. Anderson: Are you going to vacuum? Jared: Certainly, madam. We vacuum our rooms every day. Ms. Anderson: Thats good to hear. Well, its time for me to see my friends. Today were visiting a vineyard. Jared: Enjoy your day, madam. Ms. Anderson: Oh, I will†¦ Just a second, could you also take out the trolley with this mornings breakfast? Maria: Yes, madam Ill take it with me when Ive finished tidying up. More Dialogue Practice - Includes level and target structures/language functions for each dialogue.