PLC FINAL EXAM QUESTIONS AND ANSWERS
The main difference between a PLC and a relay control system is that - Answers- One
uses hardwired relay control logic and the other uses programmed instructions
The symbol in a ladder logic diagram represents a: - Answers- Virtual relay coil
At the start of the PLC scan the: - Answers- Status of all inputs are read
Unlike personal computers, PLCs are - Answers- Equipped with input and output
modules
Equipped with a control programming language
Designed for the industrial environment
A __ is an example of a device that could be used to provide a discrete input to a PLC -
Answers- Pushbutton, selector switch, limit switch
A __ is an example of an actuator that could be controlled by a discrete output from a
PLC - Answers- Motor starter
A/An __ input or output is a continuously variable signal within a designated range -
Answers- analog
A discrete output interface module is a designed to provide - Answers- on/off switching
of the output field device
Which of the following input field devices would most likely be used with an analog
interface input module - Answers- Thermocouple
The Allen-Bradley SLC 500 address I:2/4 refers to an - Answers- Input module in slot 2,
terminal 4
the purpose of the optical isolator is to - Answers- separate the higher line voltages
from the logic circuits
The input module comes from - Answers- internal logic circuitry of the processor
The purpose of the triac switch is to - Answers- turn the load on and off
For the block diagram of the analog PLC control shown, which part has a binary input
and analog output value? - Answers- Output module
Discrete I/O modules can be classified as - Answers- bit oriented
, When placed in the __ mode, the processor does not scan/execute the ladder program -
Answers- program
A human machine interface (HMI) - Answers- Allows the user to monitor a process
allows the user to control a process
can provide a graphical representation of a process
Block No. 1 of the PLC block diagram represents the - Answers- programming device
Block No.4 represents the - Answers- input module
Block No. 5 represents the - Answers- output module
Which module of the PLC connects directly to field devices such as pilot lights, motor
starters, and solenoids? - Answers- output
The decimal system has as its base - Answers- 10
Which of the following number systems has a base of 16 - Answers- Hexadecimal
One byte of the data shown is represented by - Answers- No. 1
The memory size represented is - Answers- 1 K
The acronym BCD stands for - Answers- binary-coded decimal
If a given memory unit consists of 1250 16 bit words, the memory capacity would be
rated - Answers- 20,000 bits
A gate is a device that - Answers- performs a logical decision based on its inputs
The basic rule for and AND gate is - Answers- if all inputs are 1, the output will be 1
The basic rule for an OR gate is - Answers- if one or more inputs are 1, the output is 1
A NOT function is used when a logic 1 must __ some device - Answers- deactivate
An AND gate operates on the same priciple as - Answers- a series circuit
A OR gate operates on the same principle as - Answers- a parallel circuit
The basic rule for the XOR function is - Answers- if one or the other, but not both,
inputs are 1, the output is 1
The binary number 101 has a decimal equivalent of 5 - Answers-
The main difference between a PLC and a relay control system is that - Answers- One
uses hardwired relay control logic and the other uses programmed instructions
The symbol in a ladder logic diagram represents a: - Answers- Virtual relay coil
At the start of the PLC scan the: - Answers- Status of all inputs are read
Unlike personal computers, PLCs are - Answers- Equipped with input and output
modules
Equipped with a control programming language
Designed for the industrial environment
A __ is an example of a device that could be used to provide a discrete input to a PLC -
Answers- Pushbutton, selector switch, limit switch
A __ is an example of an actuator that could be controlled by a discrete output from a
PLC - Answers- Motor starter
A/An __ input or output is a continuously variable signal within a designated range -
Answers- analog
A discrete output interface module is a designed to provide - Answers- on/off switching
of the output field device
Which of the following input field devices would most likely be used with an analog
interface input module - Answers- Thermocouple
The Allen-Bradley SLC 500 address I:2/4 refers to an - Answers- Input module in slot 2,
terminal 4
the purpose of the optical isolator is to - Answers- separate the higher line voltages
from the logic circuits
The input module comes from - Answers- internal logic circuitry of the processor
The purpose of the triac switch is to - Answers- turn the load on and off
For the block diagram of the analog PLC control shown, which part has a binary input
and analog output value? - Answers- Output module
Discrete I/O modules can be classified as - Answers- bit oriented
, When placed in the __ mode, the processor does not scan/execute the ladder program -
Answers- program
A human machine interface (HMI) - Answers- Allows the user to monitor a process
allows the user to control a process
can provide a graphical representation of a process
Block No. 1 of the PLC block diagram represents the - Answers- programming device
Block No.4 represents the - Answers- input module
Block No. 5 represents the - Answers- output module
Which module of the PLC connects directly to field devices such as pilot lights, motor
starters, and solenoids? - Answers- output
The decimal system has as its base - Answers- 10
Which of the following number systems has a base of 16 - Answers- Hexadecimal
One byte of the data shown is represented by - Answers- No. 1
The memory size represented is - Answers- 1 K
The acronym BCD stands for - Answers- binary-coded decimal
If a given memory unit consists of 1250 16 bit words, the memory capacity would be
rated - Answers- 20,000 bits
A gate is a device that - Answers- performs a logical decision based on its inputs
The basic rule for and AND gate is - Answers- if all inputs are 1, the output will be 1
The basic rule for an OR gate is - Answers- if one or more inputs are 1, the output is 1
A NOT function is used when a logic 1 must __ some device - Answers- deactivate
An AND gate operates on the same priciple as - Answers- a series circuit
A OR gate operates on the same principle as - Answers- a parallel circuit
The basic rule for the XOR function is - Answers- if one or the other, but not both,
inputs are 1, the output is 1
The binary number 101 has a decimal equivalent of 5 - Answers-
