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
, 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
3) 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
4) 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
5) 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
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
, 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
3) 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
4) 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
5) 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
