6.1 State TWO advantages of a programmable logic controller (PLC) compared to a hard-wired system - NSC Electrical Technology Electronics - Question 6 - 2016 - Paper 1
Question 6
6.1 State TWO advantages of a programmable logic controller (PLC) compared to a hard-wired system.
6.2 Draw a block diagram of a PLC scan cycle showing the THREE st... show full transcript
Worked Solution & Example Answer:6.1 State TWO advantages of a programmable logic controller (PLC) compared to a hard-wired system - NSC Electrical Technology Electronics - Question 6 - 2016 - Paper 1
Step 1
State TWO advantages of a programmable logic controller (PLC) compared to a hard-wired system.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Reduced Space: PLCs are solid-state devices that occupy less physical space compared to traditional hard-wired systems, allowing for a more compact installation.
Faster Response Time: PLCs can process thousands of operations per second, leading to quicker response times in automation tasks.
Step 2
Draw a block diagram of a PLC scan cycle showing the THREE steps that are used to execute a programme. Label each step and indicate its function.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Input Check: This stage involves checking the status of all inputs connected to the system through an input interface.
Process: During this phase, the PLC executes the programmed instructions based on the input data received.
Output Update: This final step updates the outputs according to the processed instructions, initiating any connected actuators or indicators.
Step 3
Name TWO output devices that may be connected to a PLC.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Motor Contactors: Used to control electrical motors.
Indicator Lamps: Provide visual signals indicating the status of the system.
Step 4
Simplify the equation below using Boolean algebra:
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Starting with the equation:
F=AB′C+A′BC+ABC+AB′C+AB+C
Using Boolean algebra:
Combine like terms:
F=AB′C+A′BC+ABC+AB+C=AB′C+C+AB
Factor out common terms:
=C+AB
Thus, the simplified equation is:
F=C+AB
Step 5
Name THREE programming methods used to instruct a PLC.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Ladder Diagrams: A visual programming approach that resembles electrical relay logic.
Function Blocks: Modular programming using blocks that represent various functions.
Sequential Functions Chart: Diagrammatic representation of sequences of operations.
Step 6
Convert the equation into a Karnaugh map.
97%
121 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To convert the equation F=ABCD+AB′C+ABCD+AB′CD+AB′C into a Karnaugh map, first group the products by placing them in the appropriate cells of the map based on common values of A, B, C, and D. Label each grouping accordingly.
Step 7
Derive and write the simplified Boolean equation from the Karnaugh map in your ANSWER BOOK.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
After grouping the terms in the Karnaugh map, the simplified Boolean equation can be derived as:
Y=B′C′D′+AB+C
Step 8
Identify the circuit in FIGURE 6.1.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The circuit shown in FIGURE 6.1 is a relay control circuit, which typically includes components like lamps, timers, and motor controls to manage electrical tasks with relays.
Step 9
Draw the PLC ladder diagram that would execute the relay control circuit in FIGURE 6.1. Your diagram must include a marker or a flag function.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The PLC ladder diagram would consist of rungs wired to represent the relay control actions:
The first rung checks if the O/L (Overload) condition is not met.
The following rungs process the input conditions from Start 1 and Start 2, utilizing timers and flags to maintain operational continuity.
The final output rungs could control the lamp and motor states.
Step 10
Explain why the marker or flag is used in the drawing of the ladder diagram in QUESTION 6.7.2.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Markers or flags are used in PLC programming to hold a condition or state during operation. They simplify the control logic by maintaining certain state information, allowing for more complex sequences and preventing unintended resets of outputs. This helps in structuring the logic more clearly and effectively.
