LOGIC GATES AND PROGRAM LOGIC CONTROLLER

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• Q1: What is a Programmable Logic Controller (PLC)?
  Ans: A PLC is an electronic device used to control machines and industrial processes automatically using programmed instructions.
• Q2: State the uses of PLC.
  Ans: Uses of PLC are:

  • ➔ Industrial automation
  • ➔ Machine control
  • ➔ Process control systems
  • ➔ Traffic control systems
• Q3: State any six advantages of PLC.
  Ans: Advantages of PLC are:

  • ➔ High reliability
  • ➔ Easy to program
  • ➔ Less wiring required
  • ➔ Flexible operation
  • ➔ Easy maintenance
  • ➔ Fast operation
• Q4: State the limitations of PLC.
  Ans: Limitations of PLC are:

  • ➔ High initial cost
  • ➔ Requires skilled programmer
  • ➔ Limited for small applications
  • ➔ Needs proper environment
• Q5: Define Logic.
  Ans: Logic is the process of making decisions based on given conditions.
• Q6: Define Ladder Logic.
  Ans: Ladder logic is a graphical programming language used in PLC that resembles a ladder diagram.
• Q7: Define Rungs.
  Ans: Rungs are the horizontal lines in a ladder logic diagram where instructions are written.
• Q8: Define Relay Logic.
  Ans: Relay logic is a control system that uses relays to perform logical operations.
• Q9: State the basic components of PLC.
  Ans: The basic components of PLC are:

  • ➔ Central Processing Unit (CPU)
  • ➔ Programming Keyboard and Monitor
  • ➔ Input and Output Modules
• Q10: Briefly explain the working of PLC.
  Ans: PLC receives input signals from sensors.
  
  The CPU processes the program logic.
  Then it sends output signals to control devices like motors and relays.
• Q11: What are Logic Gates?
  Ans: Logic gates are electronic circuits that perform logical operations on one or more inputs to produce an output.
• Q12: Name the types of Logic Gates.
  Ans: Types of logic gates are:

  • ➔ AND Gate
  • ➔ OR Gate
  • ➔ NOT Gate
  • ➔ NAND Gate
  • ➔ NOR Gate
  • ➔ XOR Gate
  • ➔ XNOR Gate
• Q13: What is an AND Gate?
  Ans: An AND gate gives output HIGH only when all inputs are HIGH.
• Q14: State the uses of AND Gate.
  Ans: Uses of AND gate are:

  • ➔ Used in control circuits
  • ➔ Used in safety systems
  • ➔ Used in digital circuits
• Q15: What is an OR Gate?
  Ans: An OR gate gives output HIGH if any one input is HIGH.
• Q16: State the uses of OR Gate.
  Ans: Uses of OR gate are:

  • ➔ Used in alarm systems
  • ➔ Used in control circuits
  • ➔ Used in decision making circuits
• Q17: What is a NAND Gate?
  Ans: A NAND gate gives output LOW only when all inputs are HIGH.
• Q18: State the uses of NAND Gate.
  Ans: Uses of NAND gate are:

  • ➔ Used in digital circuits
  • ➔ Used as universal gate
  • ➔ Used in logic design
• Q19: What is a NOR Gate?
  Ans: A NOR gate gives output HIGH only when all inputs are LOW.
• Q20: State the uses of NOR Gate.
  Ans: Uses of NOR gate are:

  • ➔ Used as universal gate
  • ➔ Used in digital circuits
  • ➔ Used in memory circuits
• Q21: What is an XNOR Gate?
  Ans: An XNOR gate gives output HIGH when inputs are equal.
• Q22: State the uses of XNOR Gate.
  Ans: Uses of XNOR gate are:

  • ➔ Used in comparators
  • ➔ Used in equality checking circuits
  • ➔ Used in digital systems
• Q23: What is a NOT Gate?
  Ans: A NOT gate gives the opposite output of the input.
• Q24: State the uses of NOT Gate.
  Ans: Uses of NOT gate are:

  • ➔ Used for signal inversion
  • ➔ Used in digital circuits
  • ➔ Used in logic design
• Q25: What is an XOR Gate?
  Ans: An XOR gate gives output HIGH when inputs are different.
• Q26: State the uses of XOR Gate.
  Ans: Uses of XOR gate are:

  • ➔ Used in adders
  • ➔ Used in error detection
  • ➔ Used in digital circuits
• Q27: What is a Digital Number System?
  Ans: A digital number system is a method of representing numbers using digits.
• Q28: What is the Decimal Number System?
  Ans: Decimal number system uses base 10 and digits from 0 to 9.
• Q29: What is the Binary Number System?
  Ans: Binary number system uses base 2 and digits 0 and 1.
• Q30: What is the Octal System?
  Ans: Octal number system uses base 8 and digits from 0 to 7.
• Q31: What is the Hexa-Decimal Number System?
  Ans: Hexadecimal system uses base 16 and digits 0–9 and A–F.
• Q32: Define Positive Logic.
  Ans: Positive logic means HIGH voltage represents 1 and LOW voltage represents 0.
• Q33: Define Negative Logic.
  Ans: Negative logic means LOW voltage represents 1 and HIGH voltage represents 0.
• Q34: What is the Truth Table?
  Ans: A truth table is a table that shows all possible input combinations and their corresponding outputs.
• Q35: Convert (14)10 into Binary.
  Ans: Step 1:
  Divide 14 by 2 → remainder 0
  Step 2:
  Divide 7 by 2 → remainder 1
  Step 3:
  Divide 3 by 2 → remainder 1
  Step 3:
  Divide 1 by 2 → remainder 1
  Write remainders in reverse order:
  (14)₁₀ = (1110)₂
• Q36: Convert (0.101)2 into Decimal Number.
  Ans: Step 1:
  1 × 2^-1 = 0.5
  Step 2:
  0 × 2^-2 = 0
  Step 3:
  1 × 2^-3 = 0.125
  Add values:
  0.5 + 0 + 0.125 = 0.625
  (0.101)₂ = (0.625)₁₀
• Q37: Convert (1101)2 into Decimal Number.
  Ans: Step 1:
  1 × 2³ = 8
  Step 2:
  1 × 2² = 4
  Step 3:
  0 × 2¹ = 0
  Step 4:
  1 × 2⁰ = 1
  Add values:
  8 + 4 + 0 + 1 = 13
  (1101)₂ = (13)₁₀
• Q38: How can we convert Decimal Number into Octal Number.
  Ans: To convert decimal to octal:
  
  Step 1:
  Divide the number by 8
  Step 2:
  Note the remainder
  Step 3:
  Continue division until quotient is 0
  Step 4:
  Write remainders in reverse order to get octal number