Describe four types of sensors that could be connected to a PLC to enable it to control an industrial process

In an industrial application, identify the use of ADC and DAC in  the system.


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1.Assignment Title : Design of operational characteristics of programmable logic control  systems

2.Learning Outcome(s) covered :

LOC 1: Understand the design and operational characteristics of a PLC system.

LOC 2: Understand PLC information and communication techniques.


3.Programme Learning Outcome(s) and Programme Objective(s) covered :

Programme Objective :

1.Provide adequate technical knowledge and skills to qualified students and meet the requirement to study this field

2.Exposed to the theoretical knowledge and practical skills of Mechanical Engineering so that they can contribute to the current industry needs.


Programme Learning Outcome

PLO 2.Analyze, synthesize and summarize information critically.

PLO 5.Use their knowledge, understanding and skills to evaluate and formulate evidence-based arguments critically and identify solutions to clearly defined problem of a general routine nature.

PLO 10. Apply critical thinking through independent thought to solve problems creatively and effectively using basic principles.

PLO 11. Apply subject knowledge and understanding to address familiar and unfamiliar problems.


4. Relationship to other modules :


5.Scenario/Introduction/Background Information :

Programmable logic controllers (PLCs) have become the most predominant control elements for the discrete event control of a mechatronic system. Simplification of engineering and precise control of manufacturing process can result in significant cost savings. The most cost-effective way which can pay big dividends in the long run is flexible automation; a planned approach towards integrated control systems. It requires a conscious effort on the part of plant managers and engineers to identify areas where automation can result in better deployment and/or utilization of human resources and savings in man-hours or down time. Controls automation need not be high ended and extremely sophisticated; it is the phased, step-by-step effort to automate, employing control systems tailored to one’s specific requirements that achieves the most attractive results. This is where programmable logic controls have been a breakthrough in the field of automation and control techniques.


6.Task 1 :

a)Three styles of PLC design are known as UNITARY, MODULAR and RACK-MOUNTED. Explain what this means and what are their relative advantages and disadvantages. Include pictures and diagrams to further support your explanation.


b)A push button is an example of a device that could be used to provide a discrete input to a PLC while a motor starter is an example of an actuator that could be controlled by a discrete output from a PLC

i.Describe FOUR types of sensors that could be connected to a PLC to enable it to control an industrial process.

ii.Describe FOUR devices that may be controlled in an industrial process. Support your explanation with pictures and diagrams.


c)A PLC will be required to communicate with other devices for purposes of programming and network communication for receiving and sending digital data. A simple PLC may be part of a larger system controlled by a mainframe computer, thus the communication links are important. Evaluate the different types of communication links used in linking the PLC systems to the larger network. State their characteristics, advantages/ disadvantages, and usage in the communication links.


d)Analogue electrical signals are used to represent process variables such as pressure, speed, temperature, flow rate and so on. The instruments produce electrical outputs that are processed into a standard form so that equipment can connected to it such as analogue to digital converters. The standards used are 4 – 20 mA or 0 – 10 V.


i)Explain why modern system use 4-20 mA standard ? Find and describe briefly at least one industrial analogue sensor that would be used with the 4 – 20 mA A/D channel.

ii)A/D modules may have different word lengths giving resolutions. Calculate the resolution of a 4-bit and 12-bit A/D modules. Describe the relation of the resolution with the word size.


iii)The A/D module can be represented by tables and graphs. Represent an analogue channel of  for a 4-bit A/D module in tables and graphs. ( represents the last two digits of your student ID).


e)Computer communicate with other computers and with various parts of an engineering system such as logic controllers. The computers or the PLCs may interrogate other equipment such as counters, timers, flow meters, temperature sensors and level gauges. They may also send signals to other hardware items such as bank of pneumatic valves or a pipeline controller. Write out a full definition of the following protocols and give a comparison of them





f)Networks are becoming more and more popular every day. A single network cable provide device operating power and data transfer between many devices and the PLC processor rather than running large wiring bundles between the PLC and distant I/O field devices. PLC processors connected together afford a programmer or maintenance personal the ability to access any PLC processor from a single computer via a network connection for program downloads, editing, or monitoring. PLC processors can also communicate time-critical or interlocking information between themselves over the network. The terms listed below are used with networking standards. Describe the meaning of each.







g)The PLC activates its output terminals in order to switch things on or off. The decisions are made based on the inputs connected to the PLC which are then logically processed by the CPU. Sketch the basic internal architecture of a PLC and explain the following:

i)Structure and operational characteristics of CPU





vi)Busses (data bus and address bus)

vii)Program counter


Task 2 :

a)In an industrial application, identify the use of ADC and DAC in the system.


b)The A/D module can be represented by tables and graphs. Represent an analogue channel of  0 – XID  Volt  for a 4-bit A/D module in tables and graphs. ( XID represents the last two digits of your student ID).


c)Report your findings in (a) in detail by presenting the possible circuit and its operation used in the Application.


d)Conclude your report based of your findings in (a and b) by justifying the reasons of the usage of ADC and DAC in the system. Include examples to support your conclusion.


e)Provide plan in Based on the discussed in (c), suggest methods to improve accuracy and resolution of the ADC used.


f)Provide well-structured report with a proper referencing.



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