Industrial electronics question bank

Sukesh.R/ECE/Lecturer Industrial Electronics ECE/IV sem
UNIT - I
1. What is SCR?
Silicon Controlled Rectifier is a three terminals (Anode, Cathode and Gate), three junction and
four layer semiconductor switching device.
2. What is IGBT?
Insulated Gate Bipolar Transistor is a three terminal(Collector, Emitter, gate ) power
semiconductor device. It’s a combination of BJT and MOSFET. It is used as an electronic switch
with high efficiency and fast switching.
3. What is Triggering of an SCR?
Triggering is nothing but turned ON process of an SCR.
The SCR can be triggered (tuned ON) any one of the following methods.
Increasing forward voltage beyond breakdown voltage VBO.
Applying a positive voltage to gate with respect to cathode(Gate control method)
4. What is Opto Coupler?
An opto coupler used to isolate the low power control circuitry from a high power load.
It consists of a light source, a light sensitive device and a switching device.
OR
Transferring of an electrical energy between two circuits, without any physical contacts.
5. Define Holding Current.
It is the minimum anode current, below which SCR turned OFF.
6. Define Latching current of an SCR.
Latching current is the minimum value of anode current required to keep (continuous) the SCR in the
ON state after the gate signal is removed.
7. Define dv/dt rating
The dv/dt rating of an SCR indicates the maximum rate of rise of anode voltage that will not
trigger the SCR without any gate signal.
8. Define di/dt rating.
The di/dt rating of an SCR indicates the maximum allowable rate of change of current which the SCR
can withstand during its on state.
9.How is SCR turned OFF?
• By giving reverse voltage to the gate-cathode terminal, the SCR will turn OFF.
• By reducing anode current below holding current.
10.Define forward break over voltage of SCR.
The minimum forward voltage with gate open, at which SCR starts conducting heavily (turn on) is
called the Breakover voltage.
11.What is reverse blocking region in SCR?
In the reverse biased condition, the reverse voltage is gradually increased, at a particular voltage
avalanche breakdown occur. The region before breakdown is called reverse blocking region.
12.What is forward conduction region?
By applying a gate signal to SCR, it will goes to heavy conduction in the forward biased condition. This
region is called as forward conduction region.
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13. Mention the types of triggering.
 AC gate triggering
 DC gate triggering
 Pulsed gate triggering
14. Mention any three applications of SCR
 Emergency light
 Automatic battery charger circuit
 Large power supplies
 Industrial Applications
15. Mention any three applications of MOSFET
 Electronic DC relay
 Switched mode power supply
 Induction heating
16. Mention any three applications of IGBT
 DC and AC motor drives.
 Traction motor control
 UPS system
17. Mention any three applications of GTO
 Static breakers
 High power inverters
 Deep sea pump drives
18. Mention any two requirements of a gate triggering circuit
 The SCR should be forward biased
 Gate should be made positive with respect to cathode 
19. What are the advantages of pulse train triggering?
 Low heat is produced at the gate-cathode junction.
 The size of gate isolation transformer is small.
 Low dissipation in reverse biased state.
20. Write three advantages of GTO.
 GTO has faster switching speed
 It has lower size and weight & It has higher efficiency
 No need of commutation circuit to turn off.
21. What is GTO? Draw its symbol.
A Gate Turn off Thyristor is a special type of thyristor, a high power semiconductor device. It
contains three terminals, namely Anode (A), Cathode (K) and Gate (G). It can be turned OFF by applying
Negative gate signal to gate.

22. What is MOSFET?
Metal Oxide Semiconductor Field Effect Transistor is a very fast switching transistor. It has three
terminals called drain (D), source(S) and Gate(G).
23. Expand LASCR, SBS, SUS.
LASCR - Light Activated SCR
SBS - Silicon bilateral Switch
SUS - Silicon Unilateral Switch
24. What is Pulse transformer?
Pulse transformers are often used to couple a trigger pulse generator to a SCR, in order to obtain electrical
isolation between the two circuits.
25. Write the types of pulse triggering.
• Single pulse triggering
• Pulse train triggering
26. Define triggering circuit or firing circuit
A circuit which used to Turn ON the SCR is called triggering circuit or firing circuit.
27. What is thyristor?
Thyristor is a power Semiconductor device. It derived from the properties of a THYRatron tube and a
TransISTOR. THYRISTOR = THYRatron + TransISTOR
28. List some devices on Thyristor family.
SCR – Silicon controlled rectifier
IGBT – Insulated gate bipolar transistor
GTO – Gate turn off thyristor
MOSFET - Metal Oxide Semiconductor Field Effect Transistor
LASCR - Light Activated SCR
SBS - Silicon bilateral Switch
SUS - Silicon Unilateral Switch
29. Draw the symbols of SCR, IGBT, MOSFET and GTO
UNIT-II
1. What is Converter?
A circuit used for converting AC into DC is called converter or rectifier.
2. What is Controlled converter?
A circuit used for converting AC into DC by using SCRs is popularly known as a controlled
converter.
3. Define Phase control of an SCR.
An SCR can be turned-ON at any angle ‘α’ with respect to the applied voltage, and it is known as phase
control.

4. What is Commutation?
Commutation is defined as the process of turning OFF a SCR. (or) The process of transferring
conduction from one SCR to another SCR is termed as commutation.
5. What is Chopper?
A chopper is a static device that converts the input DC voltage into fixed or variable DC output
voltage.
6. Give two applications of DC chopper.
 Electric automobiles (battery operated vehicle)
 Trolley cars
 Industrial applications
7. Mention the two types of Commutation.
 Natural Commutation
 Forced Commutation
8. What is Natural Commutation?(Line commutation)
The SCR will be turned OFF due to the natural behavior of source voltage i.e, the current goes through
natural zero. These types of commutation are known as Natural commutation or Line commutation.
9. What is Forced Commutation?
If the input voltage of SCR is DC, then its forward current is forced to zero by using a commutation
circuit to turn OFF the SCR. This type of commutation is called as Forced Commutation.
OR
If the SCR is turned OFF by an External circuit then it is called as forced commutation.
10. What is an AC chopper
Voltage changing circuits employing semiconductor devices as a static switch, are known as AC
choppers.
11.What is Freewheeling diode?
The flywheel or free wheel diode helps to turn OFF the SCR and improves load current
waveform and provide higher DC output voltage.
12.What is DC chopper?
DC chopper converts directly from DC to DC relatively with a new technology.
13.Mention the types of phase controlled converters.
a. Single phase converters
b. Three phase converters
Each of the above types is again sub divided into
Semi converter
Full converter
Dual converter
14. Mention the advantages of the phase controlled converters
 Simple circuit
 High efficiency
 Less expensive.
15. Mention the types of forced commutation
 Class A commutation
 Class B commutation

 Class C commutation
 Class D commutation
 Class E commutation
 Class F commutation
16. Mention the methods to vary the average output voltage in DC chopper.
 Variable frequency control
 Constant frequency control
17. Define commutation circuit.
A circuit which uses to turn OFF the SCR is called Commutation circuit.
18. What is duty cycle.
Duty cycle (α) is an operating period of chopper. It’s a ratio between Ton to (Ton + Toff).
Duty cycle(α) = Ton / (Ton + Toff)
19. Give the disadvantage of Johns chopper
SCRs with higher PIV rating is required.
20. How the SCR is turned OFF?
1) its anode current falls below the holding current
2) Applying reverse voltage to SCR
UNIT-III
1. What is an inverter?
 DC to AC Converters is known as inverters.
2. Mention the requirements of an inverter
 Output waveform should be sinusoidal
 Output voltage should be controllable
 It should be able to operate with an inductive load
 It has to operated even without load
3. Give the applications of inverter
 Variable speed AC motor drives
 Emergency light circuits
 Stand-by power supplies for relays
 Stand-by power supplies for computers
4. What is UPS?
Uninterruptable power supply combines a power supply with a battery to provide a circuit can
provide output power while the incoming power is down.
It is a Stand by sources for critical loads where normal AC supplies are not available.
5. Mention the types of UPS.
 OFF- line UPS
 ON-line UPS

6. Give any two difference between online and offline UPS
S.No. OFF-line UPS ON-line UPS
1. The inverter comes into play only when
the AC mains fails
The inverter is always powered
irrespective of the AC mains
2. It introduces some delay during change
over from main to inverter, and inverter
to main
No delay during change over period.
7. Mention the advantages ON line UPS
 Always provide regulated output to load.
 It protects the load from Surges, noise frequency vibrations
 Inverter output frequency can be maintained at the desired value.
8. Mention the methods to obtain sine wave output from an inverter.
 Resonating the load
 Using proper filters
 Using pulse width modulation
 Using sine wave synthesis
 Using poly-phase inverters
9. Mention the methods to control the output voltage from an inverter.
 Control of DC input voltage of inverter
 Control of AC output voltage of inverter
 Control of voltage within the inverter
10. Mention the advantages of McMurray inverter.
 Independent half cycle control allows PWM operation.
 Higher efficiency at light loads is thus achieved.
 A portion of commutating energy is stored in an inductor and returned to the commutating
capacitor.
 Low commutation losses at lower loads.
11. What is SMPS?
Switched Mode Power Supplies provide regulated output voltage with more efficiency. They do not
require the larger transformers and filtering devices.
12. Mention the advantages of DC transmission system.
 Used for long distance electricity transmission
 Power on each DC pole is independently controllable.
 Intermediate switching stations are not required.
 No corona loss
 A DC system offers high degree of reliability at reduced cost.
 No skin effect.
13. Mention the advantages of SMPS over linear power supplies.
 For the same power rating, SMPS is smaller size lighter in weight and possesses higher efficiency.
 SMPS is less sensitive to input variations.
14. Mention five applications of SMPS.
 Televisions and monitors.
 Printers and FAX machines.

 VCRs and portable CD players.
 Computers.
 Laptop and camcorder power packs.
15. What is HVDC(High Voltage Direct Current) transmission
HVDC is used for long distance electricity transmission. When comparing with AC transmission method,
Additionally it uses converters for HVDC systems. It can transmit upto 2000V.
16. Mention the types of HVDC
1) Uni-polar HVDC – it uses single conductor only.
2) Bi-polar HVDC – it uses two conductors.
17. What is the need of control circuit in SMPS
Control circuit is consisting of feedback loop, Oscillator, comparator and duty cycle control. Control circuit
ensures the regulated output of SMPS by using above mentioned parts.
18. Expand SMPS, HVDC, UPS
SMPS - Switched Mode Power Supplies
HVDC - High Voltage Direct Current
UPS - Uninterruptable power supply
19. What is meant by duty cycle control in SMPS?
Pulse Width Modulation technic is used for Duty cycle control. It vary pulse by pulse to provide
an accurate output voltage.
20. What is parallel inverter?
During the working of inverter , the commutating capacitor (C) comes in to parallel with the
load is called Parallel inverter.
UNIT-IV
1. What is PLC?
Programmable Logic Controller (PLC) is a solid state system, with a programmable memory for
storing instructions and implements specific functions such as logic, timing, sequencing and
arithmetic to control machines and processes.
2. What is a relay?
Relay is an electrically operated device and it is used for controlling high voltage and current
devices with a low voltage and current control signal. It may have NO and NC contacts or both the
combinations.
3. What is input module?
The input devices like push buttons, limit switches, analog sensors are wired to input module which is
used to give inputs to the processor.
4. Mention the input switching device used in PLC.
 Limit switches,
 Push buttons and analog sensors.
5. Mention the output devices used in PLC.
 Contactors, solenoid valves, indicator lights and positioning valves.
6. What are the parts of PLC?
It consists of five parts. Namely, 1) Processor unit
2) Power supply

3) Memory
4) Input/output section
5) Programming Device
7. State any two advantages of PLC.
 Flexibility and lower cost
 Implementing changes and correcting errors
 Reliability and maintainability
 Easy of change by reprogramming
8. What is ladder programming?
Relay ladder logic is a graphical programming language for PLCs. The ladder diagram language is
basically a symbolic set of instructions used to create the controller program.
8. State and draw AND logic function.
In AND logic two or more switches are connected in a serial manner. The switch assembly is
used to control the load.
9. Mention the types of relays.
i)Electromechanical relay
ii)Solid state relay
iii)Timing relay
iv)Latched relay
10. Give the features of PLC.
i)The input and output status are individually indicated
ii)Separate display comments are available
iii)It provides isolation between input and output.
11. Give any two difference between PLC and hardwired circuit.
S.no. PLC circuit Hardwired circuit
1. It is a programmable one. So
modification is easy.
Relays have to be hardwired to perform a
specific function. So modification is difficult.
2. Power consumption is reduced Power consumption is high
3. Very reliable operation Non- reliable
4. Speed of operation is High Speed of operation is Low
12. Mention the types of I/O module.
i) Analog I/O ii) Digital (Discrete) I/O
13. What is timing relay (Timer)?
Timing relays are conventional relays , which used to provide time delay for opening or closing the contacts.
14. What are the types timing relay OR Timer
1) ON delay timing relay ( DOE- Delay On Energize)
2) OFF delay timing relay (DODE- Delay On De-Energize)
15. What is ON delay?
When the supply is given to coil, the contacts changes its positions (NO/NC) after some delay. It also called
Delay on Energize(DOE).
16. What is OFF delay?
When supply is given to relay coil, the contacts are immediately changes its position (NO/NC) and after some
delay it backs to its normal position.

17. What is meant by latching or latching relay?
Latching is a process of hold the relay on ON condition after power has been removed.
18. Give some examples of Analog input devices and digital input devices.
Example for Analog i/p devices – Sensors, Temperature probes
Example for Digital i/p devices – Push buttons, Limit switches
19. Give some examples of Analog output devices and digital output devices.
Analog o/p devices – Positioning Valves
Digital o/p devices – Contactors, relays , solenoid valves
20. What is meant by Analog i/o and digital i/o modules?
Digital I/O sections – are either ON or OFF / Energize or De-Energize
Analog I/O sections – it have infinite number of possible values
21. What is the use of processor in PLC?
Processor is a brain of a PLC. It reads and executes the operations according to the instructions.
22. What is the need of memory device in PLC?
Memory device is used to stores the instructions given in the programs. It uses ROM, RAM and EEPROM.
23. Write the types of Memory.
24. Draw the Symbols for Input and Output Device.
UNIT-V
1. What is stepper motor?
Stepper motor is a motor which rotate step by step in both clockwise and anticlockwise direction.
2. Define CNC.
Computer Numerical Control performs all the basic function by program. The programs are stored in the
memory. In CNC process involves a small digital computer.
3. Mention the application of numerical control.
 Drilling machine
 lathes and grinders
System Memory (ROM)
Application Memory
User instruction Memory (RAM) Variable Data Memory (EEPROM)
MEMORY

 Flame cutters
 Milling machines
4. Write the advantages of Numerical control systems.
 Highly flexible and economical.
 High accuracy at all ranges of speeds and feeds.
 Production time is low.
 No need of highly skilled operator.
5. Define Numerical Control (N/C).
Controlling a machine tool by a prepared program, which consists of series of numbers, is known as
numerical control. OR
A system which operations are controlled by insertion of numerical data.
6. What is part programming?
The program is written by using the collected data’s is known as part programming which is done
by the part programmer. The data’s taken from the drawing dimensions.
7. Write the steps for part programming?
 Collection of all data required to produce a part
 Calculation of a tool path along which the machine operations will be performed.
 Arrangement of the already given and calculated data in a standard format.
8. What is Robot?
A robot is a reprogrammable, multifunctional manipulator which are computer controlled devices, it
perform tasks usually done by humans.
9. Mention the driving devices used in Numerical control system.
Lead screw for X-axis drive, Y-axis drive & Z-axis drive. The Control Logic Unit (CLU) operates
the driving devices of the machine lead screws.
10. Mention the advantages of Robots.
 Productivity &Speed
 Quality
 Production
 Management control
11. Mention the parts of Post processor.
Post processor consists of,
 Input element
 Motion element
 Auxiliary element
 Output element
 Control element
12. Define Post processor.
Post processor is additional computer program. It generates output in a control tape or punched tape by
using standard peripheral devices.
Post processor translates the processed information from the computer into the coded instructions
necessary for operating the N/C system.

13. Mention the two differences between NC and CNC.
S.No. Numerical control Computer numerical control
1. Program stored in punched tape Program stored in computer memory
2. Repeated use of paper tape will destroy it Since program is stored in memory no such problem
arises
3. Making changes in program is very difficult Making changes in program is vey easy.
14. What is interpolator?
It supplies current velocity commands between two data points taken from the drawing. For
complicated parts, the required additional data points will be calculated automatically by an
interpolator.
Interpolator permits the generation of circular, slope, and parabolic paths with high degree of
accuracy.
15. What are the various post processor elements?
• Input element
• Motion element
• Auxiliary element
• Output element
• Control element
16. List the types of tape reader.
 Mechanical type
 Photo electric type
17. State the advantages of CNC system.
 Increased flexibility
 Reduction in hardware circuits
 CNC is compatible with DNC
18. What are the parts of Numerical Control(N/C) machine?
1) N/C program part (punched tape)
2) Machine Control Unit (MCU)
3) Machine
19. What are the parts of MCU (Machine control Unit)
1) Data processing Unit (DPU)
2) Control Logic Unit (CLU)
20. What is Data Processing Unit (DPU)?
Data processing unit receives the coded information from a tape, and it decodes it to the CLU.
21. What are the parts of DPU?
1) Data input device
2) Tape reader circuit
3) Decode circuits
4) Interpolator

22. What are data’s contains in DPU?
1)Position of each axis
2)Directions of motion
3)Auxiliary function
4)Dimensions ( length, speed, width etc.,)
23. What is CLU ? and What are the units of CLU (control logic unit)?
CLU operates the driving devices based on the program punched in tape.
Units of CLU:
1) Position Control Loop
2) Velocity or Speed control loop
3) Auxiliary circuits
24. Mention some programming systems for Numerical control system (N/C)
1. APT – Automatic programmed tools
2. ADAPT – Adaption of APT
3. EXAPT – Extended subset of APT
4. AUTOSPOT- Automatic system and positioning tools
5. AUTOMAP
6. AUTOPROMPT
7. CAMP II
8. SPLIT
25. What is meant by sprocket channel?
Series of equal width pulses, which produced from the punched tape. Sprocket holes are smaller than the data
holes.
26. Mention the types of data processing techniques on Part programming.
Manual Programming
Computer programming
27. What is manuscript?
Manuscript is a planning chart or list of instructions to describe the operations of machine.
Manuscript is typed with flexo writer on Punched tape or paper.
28.Write the advantages of using computer for part programming?
1) Perform the mathematical calculations quickly and accurately
2) high reliability
3)Elimination of Human Errors
4) easy to program.
29.what are the parts of Motion element in Postprocessor?
1) Geometry package
2) dynamic package
30. What are the types of numerical control?
1) Computer numerical control(CNC)
2) Direct Numerical control (DNC)
3) Adaptive control (AC)
31. What is time based generator? What are the functions of Pulse generator?
Time based Generator (TMG) contains the main clock of 2.5MHz pulse generator for the system.
Functions of Pulse generator:
Direct feeding of control loops
Generating reference signals
Producing interrupt pulses

32. How the computer is connected with the controller of CNC?
Controller is connected with computer by following lines:
Interrupt Input Lines
Digital Input Lines
Digital output Lines
33. What are the three laws of Robotics?
1) A robot must not harm humans
2) A robot must obey a human being
3) A robot must protect itself from harm
12 MARKS
UNIT 1
1. Explain SCR
2. Explain IGBT
3. Explain MOSFET
4. Explain GTO
5. Explain Gate triggering methods
6. Explain Pulse transformer triggering
7. Explain opto – isolator triggering
8. Explain RC half wave triggering and RC full wave triggering methods
9. Explain synchronized UJT triggering
UNIT 2
1. Explain single phase half controlled bridge converter with Resistive(R) load and RL load.
2. Explain single phase full controlled bridge converter with Resistive(R) load and RL load.
3. Explain the importance of fly wheel diode
OR
Explain single phase bridge converter with RL load using Flywheel diode (Half controlled & Full controlled)
4. Explain Commutation and its types (6 Marks)
5. Explain basic DC chopper operation
6. Explain jones chopper (Typical chopper)
7. Explain single phase AC chopper
8. Explain Chopper using MOSFET
UNIT 3
1. Explain Single phase full bridge inverter with Resistive (R) load and RL load.
2. Explain the methods to obtain sinewave from an inverter (6 MARKS).
3. Explain the methods to output voltage control of an Inverter
4. Explain McMurray inverters
5. Explain parallel inverter using IGBT
6. Explain HVDC transmission with its Types
7. Explain SMPS
8. Explain UPS with its types

UNIT 4
1. Explain Relay with its types
2. Explain PLC with neat block diagram
3. Explain basic Input and Output modules with neat diagrams
4. Draw ladder logic for LOGIC functions and explain it.
5. Draw ladder logic for star – delta starter and explain it.
6. Draw ladder logic for conveyor control process and explain it.
7. Draw ladder logic for Lift control process and explain it.
UNIT 5
1. Explain Numerical Control (N/C) System with neat block diagram.
2. Explain Data processing Unit and Data reading Technique.
Or
Explain Data reading or Photo electric tape reader
3. Explain Part programming
4. Explain Post processor with neat block diagram
5. Explain CNC with Neat block diagram
6. Explain basics of Robotics

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