Industrial Automation: Master of Engineering Assignment

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Master of Engineering
Industrial Automation

Table of Contents
Question 1.....................................................................................................................................3
Question 2:....................................................................................................................................4
Question 3:....................................................................................................................................6
Question 4.....................................................................................................................................6
Question 6.....................................................................................................................................7
Question 7:..................................................................................................................................11
Question 8:..................................................................................................................................12
References..................................................................................................................................14

Question 1
a) Complete the empty spaces in the following table concerning the five IEC61131-3 standard
languages.
Acronym Full Name Type of Language
LD Ladder Diagram Graphical
IL Instruction List Mnemonics
SFC Sequential Function
Chart
Graphical
FBD Function Block Diagram Graphical
ST Structured Text Textual
b) Describe in your own words what a scan cycle is.
Every PLC has a scan cycle. It is a cycle in which PLC gathers and checks the inputs, executes the
program of PLC and then updates the entire status of outputs accordingly. Response time of
PLC to input/output operations depend on the speed of the scan cycle. It is a continuous
sequential process wherein an input is gathered from the field device or field sensor, program is
executed according to the logic and as a result, output is updated to the entire module. As a
whole, this entire process is termed as PLC Scan Cycle and Scan cycle time turns out to be the
time required to complete this entire cycle.

Question 2:
a) Describe in your words how a current sourcing input module should be wired.
Input and output points that are sinking and sourcing can conduct current in one direction only
to properly connect an input module it should be wired so that it can provide a supply to
common path by connecting the input current source to the switch and to the external circuit
the input wiring is completed. this will allow the current to flow in both directions.
b) Describe in your own words what a wet relay output is.
What a wet relay output is: the output of a relay depends upon the contact upon which the
inputs supply is applied. Depending upon this contact may be wet or dry the contacts which are
rated for wet have several advantages.
The wet relay possesses characteristics of low arcing thus can be used as a switching device
where high current is frequently changing. thus we can connect a voltage level by knowing the
rated wet contact of a relay.
c) Describe in your own words what happens in practice when the behaviour of a PLC is
termed to be realtime.
Real time behaviour ensures that the output of the system is as per the specified criteria each
segment is individually analysed and thus complete output of the system is checked when PLC
is operated in real time mode each segment is operated separately and each segment has a
different color.
e) Now describe in your own words what the principal differences between a PLC program
that only handles instantaneous values versus a PLC program with memory elements are.

PLC program with instantaneous values which can be defined as a value which keeps on
alternating, so this is why they can’t be used for multiple times. On the contrary side the
memory elements are saved on the devices as they are not alternating so this provides the
advantage that it can be used for multiple times. Also, one of the key differences is that the
instantaneous values can be changed when a program is compiled. While the memory elements
which are being saved on the devices cannot be altered after running or compiling any
program.

Question 3:
3A
3B
Question 4
4(1

4(2
Question 6
5(A

5(B
6(A
6(B

6(C

Question 7:
a) Why does a PLC have a switch to choose between run and idle modes? (2 marks)
PLC uses a switch between run and idle modes in order to reliably send or receive signals to
control the whole industrial process.
b) Why do many modern PLCs have a coin battery? (2 marks)
The purpose of these coin batteries being used in modern PLCs is to provide continuous and
stable power backup in case the PLC gets disconnected from the main power source. The PLC is
the most important part of any industrial project and we cannot even think of PLC getting
disturbed for a while.
c) What are the principle differences between Cyclic scan Free-running scan Event-
triggered scan
Cyclic scan Free-running scan Event-triggered scan
Cyclic scan is faster than
the free-running scan but
is slower than the event-
triggered scan.
Free-running
scan is slower
than the cyclic
and event-
triggered scan
Event-
triggered scan
is faster than
the cyclic scan
This scan
runs with
proper logic.
This scan runs
without logic.
This scan runs
with logic.
This scan is
based on
the input
scan,
execution
with proper
logic and
scanning of
output or
program.
This scan is generally not based
on any scan or event and can be
processed according to the
need whenever required.
This scan is based upon the
triggers to initiate any other
scan or process.

Question 8:
a) Sort the content of the following table to indicate the hierarchy established in IEC61131-3
language implementation. (6 marks)
Item Hierarchy level (1 as uppermost level)
Configuration 1
Resource 2
Task 3
POU 4
Variables 5
Access Paths 6
b) Identify which of the IEC61131-3 language implementations the constructs belong to (4
marks)
Construct IEC 61131-3 Language it belongs to …
LDN Ladder logic close connector
Ladder Logic Diagram