PLC short questions

1. PLC_Technician
Part A: Short Questions
1. What are the types of control?
Ans) There are “four’ types of control.
I) on, o control, ii) sequential control, iii) feedback control, iv) logic control
2. What is the abbreviation of SPST, explain with diagram.
Ans) Abbreviation of SPST is single pole single throw.
This is a type of toggle switch. This switch has two terminals, one is pole which is
used for incoming supply another is throw which is used for outing the supply.
fig: SPST switch
3. Mention 2 software name of Schneider PLC.
Ans) I) Eco Struxure machine expert basic, ii) Control Expert or Unity Pro S
4. Mention the communication method used in PC to PLC communication.
Ans) There are many types of communication methods used in PC to PLC
communication like- Modbus, Profibus, Ethernet, USB etc.
5. What is Inching process?
Ans) Inching process is a process where we use input and output. Here input
press output ON and input release output OFF.
6. What are the types of Signals?
There are two types signal Analog signal & Digital signal.
7. What is the abbreviation of SPDT, explain with diagram.
The SPDT stands for single pole double throw. This is a type of toggle switch. This
switch has three terminals, one is pole which is used for incoming supply
another two is throw (0ne NO and one NC) which is used for outing the supply.
8. Mention the software name used for M340 and M200 PLC.
Ans- For M340 software name is Unity Pro S or Control Expert
For M200 PLC software name is Eco structure machine expert basic

2. 9. What are the types of communication possible in a PLC.
Ans) There are 3 types of Communication available in PLC.
1.Module to Module communication
2.PC to PLC communication
3.PLC to PLC communication
10.What is latching process?
Ans) latching process is a process where we use input and output. Here input
press output ON and input release still output will be in on condition.
11.Mention the types of Programming languages.
Ans- There are 5 types of programming languages available in PLC.
1.Ladder Logic Diagram (LD)
2.Function Block Diagram (FBD)
3.Instruction List (IL)
4.Structured Text (ST)
5.Sequential Function Charts (SFC)
12.What is Industry?
Ans-The transformation of raw material into di erent process or manufactured
goods on a very large scale is called industry.
13.Mention the types of Automation.
There are 3 types of Automation.
1.Fixed Automation
2.Programmable Automation
3.Flexible Automation
14.What are the di erent PLC brands known? (Mention at least 5 names).
1. Schneider
2. Siemens
3. Allen Bradley
4. Mitsubishi
5. Delta
15.Types of PLC.
There are 2 types of PLC.
1. Compact
2. Modular

3. 16.How to recognize a switch, mention 2 names of methods?
1.Contact parts of switch
2. Actuation mechanism
17.What is Uploading and Downloading in PLC?
Uploading and downloading are terms used when discussing the transfer of data
between a Programmable Logic Controller (PLC) and another system. Uploading
refers to sending/transferring data from the PLC into another device or computer
while downloading is transferring information from the other device back into the
PLC.
18.What is the purpose of a Sensor?
The purpose of a sensor is to detect any physical parameters and send them as
input signals to the PLC controller. Sensors can be used for measuring things,
such as pressure, temperature, and light, which help make further decisions or
actions.
19.Mention 3 safety precautions to be taken care of while working with PLC?
Safety precautions that one can take while working with PLC are:
 Disconnect power before making or breaking connections.
 Do not exceed PLC’s voltage and current ratings.
 Practice regular inspection and maintenance of PLC.
20.What are the advantages of using PLCs for automation?
It is the main component responsible for monitoring and controlling activities
within factories, production lines, or machines via its input/output modules and
CPU.
21.How does a PLC read sensors?
A PLC reads sensors through its input modules. The sensors send signals to the
input modules, which convert them into digital data for the PLC.
22.How does a PLC control motors?
A PLC controls motors through its output modules. The PLC sends control
signals to the output modules, which convert them into the appropriate form for
the motor controls.
23.What is a PLC communication module?
A communication module is a device that enables a PLC to communicate with
other devices over a network. It can support various protocols and media.

4. 24.What are some best practices in PLC programming?
Best practices include planning and designing the program before starting to
code, commenting on the code, testing, and simulating the program, and
maintaining good documentation.
25.What is a PLC rack or chassis?
A rack or chassis is a physical structure that holds the PLC modules. It
provides the backplane that enables communication between the
modules.
26.What is remote I/O in a PLC system?
Remote I/O refers to input and output modules that are located away from the
PLC. They communicate with the PLC over a communication network.
27.What is a PLC processor or controller?
The processor or controller is the main component of the PLC that runs the
control program and manages the overall operation of the PLC.
28.What is a memory module in a PLC?
A memory module is a device that provides additional memory for the PLC. It can
be used for storing the control program, data tables, and other information.
29.What is the di erence between a PLC and a microcontroller?
A microcontroller is a small, low-cost computer on a chip, while a PLC is a
robust, industrial-grade computer designed for controlling processes and
machines.
30.What is the PLC’s role in energy management?
PLCs can play a key role in energy management by controlling and optimizing
energy-consuming processes, as well as collecting energy usage data for
analysis.
31.What is a PLC’s service life?
The service life of a PLC can be many years or even decades, depending on the
quality of the PLC, the operating conditions, and the level of maintenance.
32.How can a PLC be used in a safety system?
A PLC can be used in a safety system by controlling safety-related devices such
as emergency stops, safety interlocks.

5. 33.What is I/O mapping in a PLC?
I/O mapping is the process of assigning PLC addresses to physical inputs and
outputs.
34.What is meant by ‘normally open’ and‘normally closed’in a PLC?
In a ‘normally open’ configuration, the circuit is open until the PLC issues a
command to close it.
In a ‘normally close’ configuration, the circuit is close until the PLC issues a
command to open it.
35.What is a bit in a PLC?
A bit is the smallest unit of data in a PLC. It can have a value of 0 (o ) or 1 (on).
36.What is a word in a PLC?
A word in a PLC is a group of bits. The number of bits in a word depends on the
PLC, but it is typically 16 or 32.
37.What is the di erence between hardwired and programmable logic?
Hardwired logic is fixed and cannot be changed once implemented.
Programmable logic, as found in a PLC, can be easily changed, and adapted
through programming.
38.What is an actuator in a PLC system?
An actuator is a device that the PLC controls to perform an action. Examples of
actuators include motors, solenoids, and lights.
39.What is a PLC program?
A PLC program is a set of instructions that the PLC executes. It defines the logic
for controlling the PLC’s outputs based on its inputs.
40.What does an emergency stop in a PLC system?
An emergency stop is a control function that stops the PLC and all controlled
equipment in the fastest and safest way possible in case of an emergency.
41.What is fail-safe programming in PLC?
Fail-safe programming is a programming approach where the system is designed
to default to a safe state in case of a failure or error.
42.What is PLC hot swapping?
Hot swapping is the ability to replace or insert modules in a PLC system while it
is still powered on and running.

6. 43.What is the di erence between a digital input and an analog input in a PLC?
A digital input reads binary signals (on or o ), while an analog input reads
continuous signals that can have any value within a certain range.
44.What is a PLC simulator?
A PLC simulator is a software tool that mimics the behaviour of a PLC, allowing
the user to test and debug PLC programs without needing physical hardware.
45.What is the di erence between a digital output and an analog output in a
PLC?
A digital output sends binary signals (on or o ), while an analog output sends
continuous signals that can have any value within a certain range.
46.What is Automation?
The automatic operation or control of a equipment, a process, or a system is
called Automation.
47.PLC invented by whom and in which year?
PLC invented by Richard Dick Morley in 1968.
48.What is the product code of PLC and why that is designated as product
code?
Product code of PLC is 084 because it is the 84th
project of Bedford associates.
49.What is the di erence between inching and latching process?
In Inching process input press output ON and input release output OFF.
In latching process input press output ON and input release still output will be in
on condition.
50. What is NO and NC?
NO stands for Normally Open and NC stands for normally close. Both are state of switches
and sensors used in PLC programming.