PLC SCADA MCQ Quiz in বাংলা - Objective Question with Answer for PLC SCADA - বিনামূল্যে ডাউনলোড করুন [PDF]

Ladder logic AND function:

• The AND function has multiple PLC inputs and has one resulting output.
• If we translate an AND function into a ladder diagram, we can express it symbolically in the form of two normally open (NO) contacts (PLC inputs A and B) and a relay coil (PLC output Y) in series.

 It is similar to logic expression

• If ‘A’ and ‘B’ then ‘Y’.

Here the ‘AND’ function examines if all the PLC inputs are TRUE, then the corresponding result is TRUE, however, if anyone of the PLC inputs is FALSE then the corresponding result is also FALSE.

PLC inputs A and B follows the binary concept and is part of the AND function there are four possible logic iterations.

The truth table of AND function is given below:

Note:

The number of logic iterations increases with an increase in the number of PLC inputs (2^{PLC inputs}). But it doesn’t matter too much with the AND function because the result can be TRUE only and only if all the PLC inputs are TRUE.

Ladder logic OR function:

If we translate on OR function into a ladder diagram we can express it symbolically in the form of two normally open (NO) contacts (PLC inputs A and B) and a relay coil (PLC output Y) in parallel.

The truth table of the OR function is given below:

Input of PLC:

• The two types of PLC inputs are commonly referred to as DI and AI (Digital and Analog).
• Analog Inputs include temperature sensors/transmitters, current sensors, voltage sensors, and others that can convert a physical quantity to an electrical signal.
• These electrical signals used for PLC input are typically 4-20 mA or 1-5 V DC.
• Digital Inputs include push buttons, limit switches, relay contacts, proximity switches, photo sensors (On/Off), pressure switches, and more. Digital inputs devices are available in both DC as well as AC and some are voltage-independent such as a switch contact.

PLC and SCADA:

• The primary difference between a PLC (Programmable Logic Controller) and SCADA (Supervisory Control and Data Acquisition) is that a PLC is hardware and SCADA is software.
• PLCs are designed to control complex industrial processes, such as controlling electrical machines.
• They are simple to program and fully scalable to an operation’s requirements.
• They’re also used to collect data from the systems they control.
• SCADA is a central system used to monitor and run the processes.
• SCADA is typically software installed on a computer, and one of its major functions is to act as an interface with industrial machines (or Human-Machine Interface, or HMI).
• SCADA systems are often used in conjunction with PLCs and other devices.
• Data from PLCs and Remote Terminal Units (RTUs) are relayed to the system, and commands are entered into the HMI to make adjustments to the processes they control.

The term PLC stands for the Programmable Logic Controller.

PLC is known as a ‘hard real-time system’.

The mass advantage of PLL over ‘hard-wire’ type relay control systems, is that PLC land themselves is functional changes very easily.

Mass components of PLC are:

• Rock or chassis
• Power supply
• Central Processing Unit (CPU)
• Communication modules
• Input and outputs

Modes of operation of PLC: There are two modes of operation:

• Program mode
• RUN mode

Program Mode: 

It is used to enter a new program, edit or update the existing program, upload files, and download files. Also, in this mode of operation, all outputs are de-energized.

Run Mode: 

It is used to execute the user program. Remote PLC programming or mode selection is dissolved when the keys are in the Run mode position. In this mode, the output is energized. It does not allow program entry editing in this mode of operation of PLC.

A programmable logic controller (PLC) or programmable controller is an industrial digital computer which has been adopted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high-reliability control and ease of programming and process fault diagnosis.

Early (PLC) was designed to replace relay logic systems. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic.

The correct answer is (option 4) i.e. RTU

Explanation:

RTU (Remote terminal unit):

A remote terminal unit (RTU) is a microprocessor-controlled device that interfaces measured physical quantity to a distributed control system or SCADA system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects.

Additional Information

HMI (Human-machine interface):

It is a user interface that is a combination of hardware and software that permits easy interaction between humans and machines.

Such an interaction between humans and machines is to control and monitor the processes ongoing at the remote locations without physically being present at that particular location.

The human-machine interface is a crucial component of automated industrial processes and thus is of significant importance in SCADA systems.

MTU (master terminal unit):

Master terminal units (MTU) in SCADA system is a device that issues the commands to the Remote Terminal Unit (RTUs) which are located at remote places from the control, gathers the required data, stores the information, and process the information, and display the information in the form of pictures, curves, and tables to human interface and help to control decision.

Components of SCADA:

A basic SCADA system consists of the following components:

• Human Machine Interface
• Supervisory System
• Remote Terminal Units (RTU)
• Programmable Logic Controllers (PLCs)
• Communication Infrastructure
• SCADA Programming

PLC Ladder Logic:

• It is visual programming language is a PLC programming language called ladder logic or ladder diagram (LD).
• It is a graphical PLC programming language that expresses logic operations with symbolic notation using ladder diagrams.
• The ladder logic program consists of Virtual relay-type contacts and coils​.
• It looks very similar to electrical relay circuits.
• Ladder logic is mainly for bit logic operations, although it is possible to scale a PLC analog input.
• Ladder logic is a fast and simple way of creating logic expressions for a PLC in order to automate repetitive machine tasks and sequences.
• It is used in a multitude of industrial automation applications.

Some industrial automation applications are Ball Mill Lubrication System, Logistics Package Conveying and Sorting, Cement Batching, etc

Example of Ladder Logic Function blocks:

1. AND Function blocks:

2. OR Function blocks:

3. X-OR Function blocks:

Application:

Given ladder logic,

Step 1: A & B is AND function block, hence ladder becomes,

Step 2: AB & D is OR function block, hence ladder becomes,

Now, both contact is in AND operation,

Hence, Output = C(AB + D)

The MVM instruction in PLC stands for Masked Move Instruction.

The MVM instruction is a word instruction that moves data from a Source location to a Destination location.

The Masked Move instruction allows portions of the Destination data to be masked by a separate word.

The MVM command is an instruction placed on the right side of the rung.

The MVM is similar to the MOV instruction in that it moves a copy of a value from a Source to a desired Destination.

Where the two instructions differ is that the MVM instruction allows portions of the Source data to pass through a mask, which is a separate word, to the Destination address.

This instruction is carried out on each scan providing the rung conditions are true. The Source value is unchanged by this command.

There are three parameters, Source, Mask, and Destination (Dest) associated with the masked move command:

• Source is a constant or the address of a word (such as I:1, S:3, N7:0, B3:3, or T4:0.ACC) of the data you want to move.
• Mask is the address of a word (such as I:1, S:3, N7:0, B3:3, or T4:0.ACC) of the data through which the Source data is filtered (See Note). The Mask value can be entered in as binary, decimal, or hexadecimal. The value for the Mask will be displayed in hexadecimal. Conversions are made courtesy of RSLogix500.
• Dest is the operator specified address of a word (such as I:1, S:3, N7:0, B3:3, or T4:0.ACC) where the data is to be move.

SCADA:

The control in SCADA is Supervisory control because SCADA is a Supervisory Control and Data Acquisition system.

It is a type of control system architecture used for the management of high-level processes.

It stores information from the remotely located data collection sensors and transducers to support the control of equipment, devices, and automated functions.

It is a centralized system that monitors and controls entire sites, ranging from an industrial plant to a complex of plants across the country.

It is used in industries like energy, oil, and gas, water, power, etc.

Explanation:

• A Programmable Logic Controller, or PLC for short, is simply a special computer device used for industrial control systems.
• They are used in many industries such as oil refineries, manufacturing lines, conveyor systems and so on. Where ever there is a need to control devices the PLC provides a flexible way to "softwire" the components together.
• PLCs come in many shapes and sizes.  They can be so small as to fit in your shirt pocket while more involved controls systems require large PLC racks. 
• I/O – The PLC’s CPU stores and processes program data, but input and output modules connect the PLC to the rest of the machine; these I/O modules are what provide information to the CPU and trigger specific results.
• I/O can be either analog or digital; input devices might include sensors, switches, and meters, while outputs might include relays, lights, valves, and drives. Users can mix and match a PLC’s I/O in order to get the right configuration for their application.

Option 1 and 4 are wrong because

• PLC does not replace microprocessor infact it is a part of PLC.
• It does not require extensive wiring by PLC.