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PLC Exam Questions and Answers: Ladder Logic and Control Systems, Exams of Nursing

University of CambridgeNursing

A series of questions and answers related to programmable logic controllers (plcs) and ladder logic programming. It covers fundamental concepts such as ladder logic elements, data types in plclogix, and the use of xic and xio instructions. The document also explores advanced topics like latching coils, transitional contacts, timers, counters, and program control instructions, offering insights into their applications and functionalities. It serves as a study guide for understanding plc programming and its practical implementations, useful for students and professionals in automation and control engineering. (404 characters)

Typology: Exams

2024/2025

Available from 07/14/2025

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rosze-macharia 🇬🇧

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ME4480 PLC EXAM
What is a ladder logic? - Answer-ladder logic is a form of programming that uses schematic diagrams
entered into programmable logic controllers (PLC). Expresses logic with symbolic notation, similar to a
logic circuit.
What is the difference between ladder logic and relay logic? - Answer-Relay logic is a ladder language
element that sets instructors that indicate the ability of the ladder language to replace control circuits
originally designed for relay networks with a control system.
3) What are the elements of ladder logic? - Answer-Relay logic
Data transfer instructions
4) What are tags/ addresses? - Answer-Variable names that define the location point in memory
5) What all data types exist in PLCLogix? - Answer-i. Boolean (BOOL)
ii. Short Integer (SINT)
iii. Integer (INT)
iv. Double Integer (DINT)
v. Real Numbers (REAL)
1) What is the need to XIC, XIO instruction? - Answer-XIC and XIO allow for the certain functions to be on
or off when start is pushed.
XIC (Examine if Close): - Answer-Instruction is programmed to test for an ON
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Download PLC Exam Questions and Answers: Ladder Logic and Control Systems and more Exams Nursing in PDF only on Docsity!

ME4480 PLC EXAM

What is a ladder logic? - Answer-ladder logic is a form of programming that uses schematic diagrams entered into programmable logic controllers (PLC). Expresses logic with symbolic notation, similar to a logic circuit. What is the difference between ladder logic and relay logic? - Answer-Relay logic is a ladder language element that sets instructors that indicate the ability of the ladder language to replace control circuits originally designed for relay networks with a control system.

  1. What are the elements of ladder logic? - Answer-Relay logic Data transfer instructions
  2. What are tags/ addresses? - Answer-Variable names that define the location point in memory
  3. What all data types exist in PLCLogix? - Answer-i. Boolean (BOOL) ii. Short Integer (SINT) iii. Integer (INT) iv. Double Integer (DINT) v. Real Numbers (REAL)
  4. What is the need to XIC, XIO instruction? - Answer-XIC and XIO allow for the certain functions to be on or off when start is pushed. XIC (Examine if Close): - Answer-Instruction is programmed to test for an ON

If reference is ON processor will close the contact to provide power flow If reference is OFF processor will to change Rung will only be evaluated if our switch is closed XIO (Examine if Open): - Answer-Whenever a test for an OFF condition is required from ref If XIO has a OFF the instruction will continue to provide logic continuity through the rung If XIO has a ON the instruction will open and interrupt the power flow What is need for Latch and Unlatch coil?When is it used, how does it work? - Answer-Latch coil (SET) and unlatch (RESET) Latching maintains an energized or de-energized state after power to the output has been removed Latch coil returns to the state it was in before power was removed Used in ladder logic programs where output device is always in the proper state Unlatch (RESET) Only way to reset latched output coil Reset the latch output of the same refere en address

  1. What is the need for internal output coil? When is it used, how does it work? - Answer-Known as dummy relays or software coils, used when an output instruction is required in a program. No physical connection to the 'real world' device
  2. What is a transitional contact? - Answer-Provides a one-shot pulse when the reference trigger signal makes a transition from either ON or OFF Program will scan once, used in sequencer and math functions
  3. What are OSR, ONS and OSF instructions? - Answer-OSR (one shot rising): produces an output for one program scan when the input rises from zero to one

Timer ON-delay energize: - Answer-most used timing function, TON instruction. The contacts associated with a timer close after the timing coil has been energized, after the input is turned on there is a delay before the output is turned on Timer ON-delay de-energize - Answer-the contacts open after the timing coil has been energized for a time interval Timer OFF-delay energize: - Answer-after the input is turned off there is a delay before the output is turned off Timer OFF-delay de-energize: - Answer-contacts open and the power is removed from the controlled load Retentive Timer: - Answer-Retentive ON-delay timer (RTO), accumulated value of the RTO is not reset to zero when rung is de-energized, have to use a RES instruction

  1. In what units is the timers set up in PLCLogix? - Answer-Milliseconds
  2. How does cascading timers work? When is it needed? - Answer-Suited for timed event-driven routines. Each step must last for a predetermined period of time and must be performed in a specific order
  3. How does reciprocating work? When is it needed? - Answer-Timering functions where the output of one timer is used to rest the input of a second timer Used when constant cycling of a output is required
  4. How is retentive timer RTO different from other timers? When is it used? - Answer-RTO does not reset to zero when de-energized.
  1. What is the purpose of each element in a timer instruction for e.g., EN, .DN, .TT, preset, accumulator?
  • Answer-EN: Enable, true when the timer instruction is true DN: Done, enabled when the accumulated value and present value are equal TT: Timer Timing, true when timer is timing Present: Present time, the timer during for the timing circuit Accumulator: represents the amount of time that has elapsed from when the timing coil is energized
  1. What are the different types of counters? - Answer-Up counters: when up counter has reached preset value it will energize and output device Down counters: countdown to zero and energize and output
  2. How does cascading counters work? When is it needed? - Answer-Using the output of one counter to initiate the counting function of the second counter Need to extend a counting operation beyond the present value of the counter
  3. What is the purpose of each element in a counter instruction for e.g., EN, .DN, , preset, accumulator, CU, CD? - Answer-EN: Enable, true when the counter instruction is true DN: Done, enabled when the accumulated value and present value are equal Present: Present count, the counter during for the counter circuit Accumulator: represents the amount of count that has elapsed from when the counter coil is energized CU: count up CD: countdown
  4. What are program control instructions used for? - Answer-Provide a method of executing mini- programs and override the entire PLC system
  1. How does JSR, JMP, LBL instructions work? - Answer-JUMP: skips the designated portion of the program JSR: jumps to a function LBL: identifies the JMP target
  2. What is a Force instruction? When is it used? - Answer-Used to test and debug program Check writing to an output device
  3. Can you have nested subroutines? How does it work? - Answer-Yes, subroutine that exists within another subroutine
  4. What are sequencers? Why is it needed? Examples of typical application of sequencers? - Answer- Sequencer is the equivalent of a mechanical drum controller Drum controllers are used to reverse the direction of rotation of a motor
  5. What is mechanical equivalent of sequencers? How does it work? - Answer-Drums controllers, It is a rotary, manual switching device made up of moving contacts mounted on an insulated rotating shaft
  6. What is a sequencer chart? - Answer-A table indicating the sequence of operations of the output device
  7. What are the types of sequencer chart? Examples. - Answer-Time sequencer chart: indicated the output on the horizontal axis and time duration on vertical axis Event driven chart: indicated the outputs on the horizontal axis and inputs, or events, on the vertical axis
  8. What is masking? How does it work? With what instruction is it used? - Answer-Control which output sare allowed to become active at an given sequencer step Similar to an array or data table

If mask contains 1 → data will pass thru If mask contains 0 → data is blocked With a Binary number or hexadecimal

  1. What are the types of sequencers? - Answer-SQL: Sequencer Load, stores data into a sequencer lead array at each step of sequencer operation SQO: Sequencer Output, six values which can be varied with the function SQI: Sequencer Input, used to compare input data to data which is stored in the data table
  2. How does each sequencer instruction work? - Answer-Sequencer load works as the input were you set all the wanted output, the output stores the data and the input compares the load data (desired) to the output stored SQL: - Answer-ARRAY: First element of the sequencer array tag to which the instruction transfers data. The sequencer input array stores data for reference to detect completion of a step or fault condition. SOURCE: Is the address of the input element or array from which the instruction obtains data for its sequencer table. CONTROL: Is the tag name of the control structure that stores the instruction's status bits, instantaneous position in the array, and the length of the sequencer array itself LENGTH: Is the number of steps of the sequencer array starting at position 1. Position 0 is the start-up position. The instruction resets to position 1 at each completion. POSITION: Is the current word location in the sequencer array. The position value is incremented internally by sequencer output instructions when the rung goes high. SQO: - Answer-ARRAY: First element of the sequencer array tag from which the instruction transfers data. The sequencer output array stores data for controlling outputs. MASK: Tag name or numerical immediate value for a mask through which the instruction moves data. Used to control the number of outputs energized at any given time. DESTINATION: Is the destination address of the output word to which the instruction moves masked data from the Source.