(SEM V) THEORY EXAMINATION 2023-24 INDUSTRIAL AUTOMATION AND CONTROL

SECTION A — Very Short Answers (2 × 10 = 20)

(a) What do you mean by Industrial Automation?

Industrial Automation is the use of control systems, such as computers, PLCs, and robots, to operate machinery and processes automatically, reducing human intervention and increasing accuracy, efficiency, and safety.

(b) Advantages of Industrial Automation

Increased productivity and efficiency.          Improved product quality and consistency.

Reduced human error and labor cost.            Enhanced safety in hazardous environments.

Enables remote control and monitoring.

(c) Difference between Relay and Contactor

(d) Realize OR Gate in Ladder Programming

Two input switches A and B are connected in parallel.

Output coil energizes when A OR B is closed.
 Symbolically:

|--[ ]--|     |--[ ]--| |   A   |-----|   B   |----( ) Output 

(Parallel connection = OR logic)

(e) Explain MATH Instruction in PLC Programming

Used to perform arithmetic operations such as ADD, SUB, MUL, DIV, and SQRT on numeric data.
Example: ADD N7:0 N7:1 N7:2 → adds data from registers N7:0 & N7:1 and stores result in N7:2.

(f) What do you mean by I/O’s in PLC?

Inputs: Devices sending signals to PLC (e.g., sensors, switches).

Outputs: Devices controlled by PLC (e.g., motors, lamps, solenoids).
Together they form the interface between the real world and the PLC controller.

(g) Benefits of HART Protocol

Combines analog (4–20 mA) with digital communication.

Allows remote calibration, configuration, and diagnostics.

Compatible with existing 4–20 mA loops (backward compatible).

Supports multivariable data communication.

(h) Advantages and Disadvantages of 4–20 mA Loops

Advantages:

Noise immunity and long-distance transmission.

Live-zero (4 mA) allows fault detection (broken wire = 0 mA).
Disadvantages:

Limited to one variable per loop.

Signal degradation possible over long distances due to resistance.

(i) What do you mean by Dew Point?

It is the temperature at which air becomes saturated with moisture and water vapor begins to condense into dew.
Used to measure humidity and air dryness in industrial processes.

(j) Explain Absolute and Relative Humidity

Absolute Humidity: Actual mass of water vapor per unit volume of air (g/m³).

Relative Humidity (RH): Ratio of actual vapor pressure to saturation vapor pressure × 100%.

RH=PactualPsaturation×100%RH = \frac{P_{actual}}{P_{saturation}} \times 100\%RH=Psaturation​Pactual​​×100% 

 SECTION B — Descriptive Questions (Any 3 × 10 = 30)

(a) Major Functions of a SCADA System

Data acquisition from field devices.                       Real-time monitoring and visualization.

Control of industrial processes remotely.               Data logging, trending, and alarms.

Communication with PLCs/RTUs using protocols (Modbus, DNP3).

(b) DOL Starter (Direct-On-Line Starter)

Used to start induction motors directly at full voltage. Components: Contactor, overload relay, start/stop push buttons.
Operation:

Press Start → contactor energizes → motor runs. Overload trip or Stop → circuit opens → motor stops.

(c) Sourcing and Sinking in PLC

Defines current flow direction between field devices and PLC I/O.

Sourcing (PNP): PLC supplies current (+V → load → input).  Sinking (NPN): PLC receives current (load → PLC → ground).
Ensures correct polarity matching between field devices and PLC.

(d) HART Protocol Working

Hybrid protocol:                     Analog signal (4–20 mA) for main variable.

Digital FSK (Frequency-Shift Keying) signal overlaid for diagnostics and additional data.
Used in smart transmitters and control systems.

(e) Components of a Pneumatic System

Compressor – provides compressed air.     Air treatment units – filter, regulator, lubricator.

Valves – control direction and flow.            Actuators – cylinders, motors for mechanical work.

Pipes and fittings – for air distribution.

(Block diagram typically includes compressor → FRL unit → valves → actuator.)

SECTION C — Long Questions (Any 1 from each)

3(a) SCADA System Components                            Master Station (Host Computer)               
 Remote Terminal Units (RTUs)                               Communication Network

Human–Machine Interface (HMI)
Provides centralized control, data storage, and alarming for large industrial plants.

4(a) Contactor – Construction & Working             Construction: Coil, magnetic core, contacts, and arc chute.

Working: When coil energizes, magnetic field closes contacts to complete the power circuit; de-energizing opens contacts.
Used for high-power switching like motors, heaters.

5(a) PLC Programming Languages (IEC 61131-3)

Ladder Diagram (LD)                             Function Block Diagram (FBD)

Structured Text (ST)                              Instruction List (IL)

Sequential Function Chart (SFC)

5(b) Timers in PLC

Types:

TON (On-Delay) – delays turning ON.      TOF (Off-Delay) – delays turning OFF.

RTO (Retentive) – accumulates time.       Timing diagram shows delay periods corresponding to instruction type.

6(a) Inductive and Capacitive Sensors

6(b) Modes of Communication for HART Devices

Point-to-Point Mode – one master, one device.       Multidrop Mode – one master, multiple devices (same current loop).                                                    Burst Mode – continuous data broadcasting from field device.

7(a) Types of Compressors in Pneumatic Systems

Reciprocating – piston compresses air.                    Rotary Screw – two meshing screws trap air.

Centrifugal – impeller increases air velocity and pressure.
Used based on flow and pressure requirements.

7(b) Realization of AND & OR Gates Using 2/2 or 3/2 Valves

AND Gate: Valves connected in series – output only when both inputs are active.

OR Gate: Valves connected in parallel – output when either input is active.
Used in pneumatic logic control.