About this previous year paper
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
| Parameter | Relay | Contactor |
|---|---|---|
| Function | Used for control and logic circuits | Used for switching high-power circuits |
| Current capacity | Low (<10 A) | High (up to 1000 A) |
| Arc suppression | Not required | Requires arc quenching |
| Application | Control logic | Motors, heaters, lighting loads |
(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=PsaturationPactual×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
| Type | Principle | Detects | Application |
|---|---|---|---|
| Inductive | Change in inductance due to metal target | Metal objects | Proximity sensing in machinery |
| Capacitive | Change in capacitance due to dielectric change | Metals & non-metals | Level or position sensing |
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.