Unit 12: Selecting and Using Programmable Controllers Report Analysis

This report provides a comprehensive analysis of Programmable Logic Controllers (PLCs), addressing various aspects of their selection, hardware, and software. It begins by differentiating between unitary, modular, and rack-mounted PLCs, illustrating their specific requirements and applications with the aid of block diagrams. The report further explores the architecture of a modern PLC system, detailing its memory, input/output interfaces, power supply, processing unit, and communication buses. It also discusses two software options, namely ladder diagrams and Functional Block Diagrams (FBD), explaining their functionalities and providing relevant diagrams. The report also covers input/output interfaces, including digital and analog types, along with the range of voltage and current used. Moreover, it identifies various field devices, such as sensors and actuators, and illustrates their connectivity. Finally, the report touches upon communication links in PLCs, including commercial examples.

Running head: ELECTRICAL AND ELECTRONIC CONTROL
ELECTRICAL AND ELECTRONIC CONTROL
Name of Student
Institution Affiliation

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TASK 1
Part a
Unitary
This type of PLC can be employed for any application which does not need several inputs and
outputs. For instance barrier in a car park (Moghe, 2016). This wouldn’t require several
inputs/output and would only need a simple program.
Modular
In this type of PLC, several inputs and outputs are used since more output/inputs can be added if
there is a need. This type of PLC is most applied in the manufacturing industry to help control
the process lines (Jamakar, 2015).
Rack-mounted programmable controller
This type of PLC is widely applied in the manufacturing industry. This is because of the
outputs/ inputs which the system can have but also due to its ability to communicate with another
network.
Part b
Unitary
Unitary PLC has a block diagram which is illustrated by the following diagram.

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Figure 1: Showing the block diagram of the unitary PLC type(Jamakar, 2015).
Some of the specific requirement for this type of PLC is given below;
 It has a single output module.
 It also has a single input module.
 Unitary PLC has a power supply.
 It has its main module which has a Central Processing Unit (CPU).

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As discussed above, this type of PLC is used in car parking, therefore this type of application is
selected for this application since in car parking there are no several processes which need to be
controlled, and it is just one process which needs to be controlled (Vogel-Heuser, 2018).
Modular
For the modular type of PLC the block diagram is illustrated as below;
Figure 2: Showing a block diagram of Modular PLC (Jamakar, 2015).
The specific requirement for the modular type of PLC is illustrated below;
 There are several input modules.
 There is a power supply.
 There are several output modules.

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 Its main module is the CPU.
For this type of PLC, there are attached to some extra output and input modules which increases
the capacity or even to cope with changes in the hardware system of this type of PLC
(Gutermuth, 2015).
This PLC finds its application in the manufacturing industry since there are several processes
which need to be coordinated therefore Modular is employed to control and coordinate those
process (several inputs / several outputs).
Rack-mounted programmable controller
Figure 3: Showing a block diagram of Rack mounted (Gutermuth, 2015).
The specific requirement for this type of PLC is the ability to communicate with another system.
Therefore this PLC best suitable application since in the manufacturing industry there are a lot of

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communications and coordination hence a lot of communications are required (Gençoğlan,
2016).
TASK 2
The system hardware of the modern PLC system can be illustrated using the following diagram;
Figure 4: Showing the architecture of modern PLC (Gutermuth, 2015).

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Some of the significant hardware of modern PLC is illustrated as below;
Memory
The PLC memory uses two basic types of memory which it uses to store data either
permanently or temporarily (Swart, 2016). These types include the ROM which is employed to
store the permanent data like the operating system as well as fixed data which will be used by
PLC. While the second type of memory known as RAM is employed in storing the temporary
data. Nevertheless, to avoid this loss of these temporarily stored data battery is used so that if the
power is turned OFF the system will utilize the power in the battery in PLC to help store the data
in RAM.
Input / output
With the several inputs and outputs modules present, the programmer can combine and
equal the modules to help fit the use which the programmer wants to attain. Digital inputs and
outputs are easy to implement in PLC. These are just implemented by switching on the signals to
represent high (1) or switching off the signals represent low signals (0).
Power supply
There must be a power supply to the PLC module to enable it to function effectively.
The power supply is not only provided to the PLC module but also the inputs and outputs. This
power system can be illustrated using the following diagram;

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Figure 5: Showing how the PLC system is powered (Gutermuth, 2015).
Basically PLC is powered by a supply of 24 VDC to about 240VAC, this in most cases fit
most of the designed voltage and current specification. The power supplied can be a lonely unit
or even an integrated into some chassis and this will depend on the producer. The supplied
power should in most cases equal the load specification of the system of PLC.
Processing unit and bus
A CPU has the framework input/output, memory and also microprocessor circuitry. The
CPU processes and controls all the functions inside the PLC. It is provided with a frequency in a
clock of regularly range of 1 and 8 MHz. This recurrence decides the working speed of the PLC
and gives the timing and synchronization for all components within the system. The data given

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in the PLC is conveyed through the means of digital signals that is to say in 1s and 0s. The
internal paths in which these signals (digital) moves is knowns as buses. In the physically, a bus
is a collection of conducting wires (copper/aluminium) which the signals flow to the whole
system.
This may be tracked on wires or even printed on the ribbon cables. These buses are very
important to the CPU since it uses them in communication with constituent elements like the
inputs and outputs. The address bus is employed to convey the addresses of places for retrieving
the data stored and the control bus for the signals linking to the internal PLC controls. The kinds
of CPU module needed shall be contingent on the requirements of the programmer, like the
operations of logic and arithmetic, client interface, local region organize availability and other
capacities. The information is sent to the information bus in the backplane. A normal scan time
cycle, will begin the scan, undertake internal checks, check inputs, perform program logic, and
lastly upgrade outputs. The capacities and selections present will change based on the model and
make utilized.
Two software options
The two of the software which can be employed to program PLC these may include the
ladder diagram, Functional Block Diagram (FBD), structured texts among others. Therefore for
this research, we will only discuss two of the mentioned software that is Ladder diagram and the
FBD.
PLC ladder simulator.

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In most operations like the industries, PLC is the most crucial automation gadget since
operates as the brain of the running processes in the industry. The industrial brain ( PLC ) use the
syntax to make it perform some tasks in a very orderly manner and in a sequential way. The
ladder is the native language which is employed in the programming PLC hence it is known as
the ladder logic. Ladder logic is basically a diagram which is can be laid in a form which looks
like a ladder hence the name ladder diagrams (Colombo, 2018). The ladder in PLC has some
rails and rungs, where the rails show the power of the PLC while the rungs indicate the process
which needs to be controlled by the PLC. This can be illustrated using the below diagram.
Figure 6: Showing the PLC ladder diagram software (Colombo, 2018).

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All the basic parameters of the PLC controls like the counters, times start and stop are
perfectly implemented in this type of software together with the inputs and outputs. For this
software there are some basic types which can be used to write this program, some of these
include the Mitsubishi, Allen Bradly, Siemens among others (Clancy, 2016). Timers and
counters are treated as the outputs, while stars and stops are treated as the inputs. A start and
hold system can be developed in a system where the start will energize another switch (which in
real life is treated as contactor relay) this will make the system to run even if the start button is
not pressed. Since this is a logic controller it uses the logic gates in its operations like NOT,
AND, OR. Where NOT is implemented by normally closed, while the AND is implemented
with two or more normally open circuit which is in series, the NOR gate is implemented using
two or more normally open circuits which are in parallel (Khan, 2016).
Functional Block Diagram
FBD is employed in PLC to program PLC using some graphical block. This is basically
a graphical language for portraying some signal as well as flows of data through the blocks and
these software elements which are reusable (Antony, 2015). Therefore a block is illustrated as in
the diagram below;
Figure 7: Showing a typical example of Functional Block Diagram (Clancy, 2016).
A function block is portrayed as a block of rectangle having inputs coming from the left
while the output of the signal moving out in the right side. The FBD type appears in the block,

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like AND, having the name of the FBD in the framework illustrated over it, for instance, counter
1 (Vogel-Heuser, 2015). Names of work square inputs appear inside the square at the suitable
input and yield units. Just like the ladder diagram, FBD can be implemented using logic
diagrams. For the FBD this is illustrated as below;
Figure 8: Showing logic gates used in programming PLC using Functional Block Diagram
(Vogel-Heuser,2015).
This FBD can be programmed in and its effects can be illustrated in a functional block in PLC as
illustrated in the diagram below;