Brendan Burr BTEC National Certificate in ElectronicsUnderstanding Selection Of Hardware and Software

Task 11.1 Describe the selection criteria and a practical application for a unitary,

modular and rack-mounted plc.

For the given plant state which system (unitary, modular and rack-mounted plc) you believe would best suit the customer’s needs and why?

Plant 1An oil rig motor control centre which requires 400 digital inputs, 240 digital outputs 38 analogue inputs, 42 analogue outputs and 5 HMI interfaces.

Rack mounted PLC – I chose this type of PLC, due to the extensive range of inputs and outputs required. There is room for expansion to meet any future specifications.Based on my research from the Allen-Bradley website I/O’s can be expanded to 128,000 digital or 4,000 analogue. This shows that there are adequate inputs and outputs potentially available for the oil rig motor control centre.

Plant 2A local plastic manufacturer with an injection moulding machine which requires 10 digital inputs, 7 digital outputs and 3 analogue inputs.

Modular PLC – I chose this type of PLC due to the option of being able to configure the PLC’s I/O’s to meet the customers demand.The availability of configuring the I/O’s means that the local plastics manufacturer could expand and integrate the existing system to work with two or more injection moulding machines, offering a much lower cost than purchasing a new PLC altogether.

Plant 3A local shop front window display which requires 3 digital inputs and 12 digital outputs.

Unitary PLC – unitary PLC’s have a limited amount of inputs and outputs and cannot be expanded. For this reason they tend to be used on smaller control systems, and are ideal for the local shop front window.This unit would cost less which would most likely suit the shop owner as the income of the shop would not be large enough to compensate on advertising in the shop window.

1

Brendan Burr BTEC National Certificate in ElectronicsUnderstanding Selection Of Hardware and Software

Task 22.1 Explain the system hardware and software requirements for a PLC.

PLC System Part NumberNumber Required

Description

PLC-5 SystemBy Allen Bradely

1Gives an adequate amount

of I/O’s and processor speeds.

PLC-5 Ethernet Processor

1

Allows the PLC-5 to communicate to other PLC-

5’s and also a Host computer.

PLC-5 Power Supply

1771-P6S1 1

Only fills one chassis slot, minimising room loss.

Further benefit of being housed inside the chassis

is there is no need for extra mounting. (1 chassis is

required)

Software9324-

RL5300ENE1

Allows the PLC to be programmed.

Digital Modules 1771-IND 25Operates at 24V AC/DC.

Has 16 digital inputs.

Analogue Modules

1771-IFF 3

Uses power from the power supply, so needs no extra

source.Has 16 single-ended

inputs.

2

Brendan Burr BTEC National Certificate in ElectronicsUnderstanding Selection Of Hardware and Software

Task 33.1 Having given the benefits and/or limitations of the unitary, modular and

rack-mounted system describe why plant 1 could only use one type and not the other two?

Plant 1 could only use a Rack Mounted PLC as there is a large amount of digital and analogue inputs and outputs required for successful operation.There is a major benefit for the oil company in purchasing a rack mounted plc. This is because the operations may alter slightly, for example new EU Regulations may affect the extraction of oil, the main advantage of PLC’s is the ability to be re-programmable, allowing the current software to be erased and rewritten.The rack mounted PLC hardware can also be upgraded to include more inputs and outputs, enabling users to broaden the range of operations the PLC can monitor. This would be done by adding another module to the existing rack mounted PLC’s.If Plant 1 used either of the remaining two types of plc, there may not be a sufficient amount of inputs and outputs, required for all of the oil pumps specifications to be met, and therefore compromise the operating parameters of the pump.The other two would not be cost effective either, as a potential upgrade would force the Oil Company to renew the whole (Hardware and Software) PLC system, rather than simple upgrading it.

3.2 For the local shop front window display (Plant 3) what benefits and/or limitations would he/she have over a more conventional relay system?

The local shop window would not require a large PLC system set up. This is because it is not necessary to have a large amount of inputs and outputs.The PLC system would have many advantages over a simple relay system such as the ability to be able to reconnect the hardware differently to create different results, whereas the shop owner would have to drastically change the relay system, costing more money in the long term.If new products or offers are put on show in the shop window, then the display can have the details entered and the information can be displayed with graphics. It would be a lot more difficult to do this if the system were composed of relays, as a the program would have to be re-written every time there are new products available.The initial cost of the PLC would be significant, however over time the system would be more cost effective, due to the necessity of having to constantly re-write the relay system software.

3