COMPLETE Programmable Logic Controllers (Petruzella) exams(all chapters) with Expert curated questions and answers + rationales (WITH DIAGRAMS)

What is a PLC (programmable logic controller)?

industrial grade computer that is capable of being programmed to perform control functions

What are some benefits of PLC's?

1. Increased reliability

2. More flexibility

3. Lower cost

4. Communications capability

5. Faster response time

6. Easier to troubleshoot

7. Easier to test field devices

The _________ is designed for multiple input and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact

PLC

What makes a PLC a real-time system?

The outputs of the system controlled by the PLC depend on the input condition

What was the PLC initially designed to replace?

Relay logic

A PLC is capable of not only performing relay switching tasks but also performing .....?

timing, counting, calculating, comparing, and processing of analog signals

What are the different parts of a PLC?

central processing unit (cpu, processor)

input/output (I/O) section

power supply

programming device

What constitutes an open architecture PLC?

a system that allows compatibility for devices and programs between manufacturers

What constitutes a closed architecture (proprietary) PLC?

a system that is proprietary which means you need to use the same manufacturer for parts (AB with AB) (Siemens with Siemens) (Most all PLC systems are proprietary)

What two ways are I/O systems incorporated into the PLC?

Fixed I/O

Modular I/O

What is Fixed I/O?

It is typical of small PLC's. The unit is non separable and has a fixed number of I/O terminals.

What is Modular I/O?

It is divided by compartments into which separate modules can be plugged into. (most PLC's)

When a modules is slid into the rack it makes an electrical connection with a series of contacts on the ______________?

backplane

What does the power supply supply power to?

In most cases ONLY the modules that plug into the rack, not the field devices

The _______ controls all PLC activity.

CPU

The PLC program is executed as part of a repetitive process referred to as a _________?

scan

What does a scan consist of?

1. Read inputs

2. Execute program

3. Update outputs

4. Diagnostics & communication

What are some examples of input devices?

pushbuttons, limit switches, sensors

What are some examples of output devices?

Motor starters, solenoid valves, indicator lights

What is a field device?

an external device physically wired in the field

What is a programming device?

a device used to enter the desired program into the memory of a processor. (usually a PC or a hand-held device)

What is a program?

a user-developed series of instructions that directs the PLC to execute actions (Relay ladder logic, function block logic)

What do the individual symbols represent on a program?

instructions

What do the numbers represent above the symbols in ladder logic?

the instruction location address

What mode does the controller need to be in, in order to run?

RUN mode

How do you measure the speed of response of a PLC?

how fast it takes to complete one scan cycle

What are the two categories in which software associated with a PLC operates on a PC?

HMI

PLC software program on computer

What is a PAC (programmable automation controller)?

It is a newer device that is a combination of a PC and PLC. It has the PLC ruggedness with PC functionality.

What criteria is used for categorizing PLC's?

functionality, number of inputs/outputs (Most Important), cost, physical size

What are the three major types of PLC application?

1. Single-ended/stand-alone PLC which involves one PLC controlling one process

2. Multitask PLC which involves one PLC controlling several processes

3. Control management PLC which involves one PLC controlling several others

What factors affect memory size needed for a particular PLC installation?

Number of I/O inputs used

Sized of control program

Data-collecting requirements

Supervisory functions required

Future expansion

What is the instruction set for a PLC?

instructions that are supported for a particular PLC

What is a PLC (programmable logic controller)?

industrial grade computer that is capable of being programmed to perform control functions

What are some benefits of PLC's?

1. Increased reliability

2. More flexibility

3. Lower cost

4. Communications capability

5. Faster response time

6. Easier to troubleshoot

7. Easier to test field devices

The _________ is designed for multiple input and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact

PLC

What makes a PLC a real-time system?

The outputs of the system controlled by the PLC depend on the input condition

What was the PLC initially designed to replace?

Relay logic

A PLC is capable of not only performing relay switching tasks but also performing .....?

timing, counting, calculating, comparing, and processing of analog signals

What are the different parts of a PLC?

central processing unit (cpu, processor)

input/output (I/O) section

power supply

programming device

What constitutes an open architecture PLC?

a system that allows compatibility for devices and programs between manufacturers

What constitutes a closed architecture (proprietary) PLC?

a system that is proprietary which means you need to use the same manufacturer for parts (AB with AB) (Siemens with Siemens) (Most all PLC systems are proprietary)

What two ways are I/O systems incorporated into the PLC?

Fixed I/O

Modular I/O

What is Fixed I/O?

It is typical of small PLC's. The unit is non separable and has a fixed number of I/O terminals.

What is Modular I/O?

It is divided by compartments into which separate modules can be plugged into. (most PLC's)

When a modules is slid into the rack it makes an electrical connection with a series of contacts on the ______________?

backplane

What does the power supply supply power to?

In most cases ONLY the modules that plug into the rack, not the field devices

The _______ controls all PLC activity.

CPU

The PLC program is executed as part of a repetitive process referred to as a _________?

scan

What does a scan consist of?

1. Read inputs

2. Execute program

3. Update outputs

4. Diagnostics & communication

What are some examples of input devices?

pushbuttons, limit switches, sensors

What are some examples of output devices?

Motor starters, solenoid valves, indicator lights

What is a field device?

an external device physically wired in the field

What is a programming device?

a device used to enter the desired program into the memory of a processor. (usually a PC or a hand-held device)

What is a program?

a user-developed series of instructions that directs the PLC to execute actions (Relay ladder logic, function block logic)

What do the individual symbols represent on a program?

instructions

What do the numbers represent above the symbols in ladder logic?

the instruction location address

What mode does the controller need to be in, in order to run?

RUN mode

How do you measure the speed of response of a PLC?

how fast it takes to complete one scan cycle

What are the two categories in which software associated with a PLC operates on a PC?

HMI

PLC software program on computer

What is a PAC (programmable automation controller)?

It is a newer device that is a combination of a PC and PLC. It has the PLC ruggedness with PC functionality.

What criteria is used for categorizing PLC's?

functionality, number of inputs/outputs (Most Important), cost, physical size

What are the three major types of PLC application?

1. Single-ended/stand-alone PLC which involves one PLC controlling one process

2. Multitask PLC which involves one PLC controlling several processes

3. Control management PLC which involves one PLC controlling several others

What factors affect memory size needed for a particular PLC installation?

Number of I/O inputs used

Sized of control program

Data-collecting requirements

Supervisory functions required

Future expansion

What is the instruction set for a PLC?

instructions that are supported for a particular PLC

radix

dsf

immediate

next to or very close to a particular place or time

chassis

the frame that a vehicle is built on

modular

consisting of separate parts or units that can be joined together

reserve

to keep something for somebody/something, so that it cannot be used by any other person or for any other reason

reside

to live in a particular place

cumbersome

slow and complicated

notation

a system of signs or symbols used to represent information, especially in mathematics, science and music

Thumbwheel

dial

to use a telephone by pushing buttons or turning the dial to call a number

alphanumeric

containing both letters and numbers

interface

to be connected with something using an interface; to connect something in this way

peripheral

a piece of equipment that is connected to a computer

Interface

protocol

a set of rules that control the way data is sent between computers

parity

carry

minuend

A number from which another number is subtracted.

subtrahend

The number that is to be subtracted.

decimal point

a dot or point used to separate the whole number from the tenths, hundredths, etc. of a decimal, for example in 0.61

whole number

a number that consists of one or more units, with no fractions (= parts of a number less than one)

Match the standard time delay symbols.

1. a

2. c

3. b

4. d

The amount of time for which a timer is programmed is called the:

a. preset.

b. set point.

c. desired time (DT).

d. all of the above.

a. preset

As scan time increases, so does the accuracy of any programmed timers. T

F

F

When the timing of a device is not reset due to a loss of power, the timer is said to be:

a. holding.

b. secured.

c. retentive.

d. continuous.

c. retentive

When more time is needed than can be programmed with one timer, two or more timers can be programmed together. This programming technique is called:

a. stacking.

b. cascading.

c. doubling.

d. synchronizing.

b. cascading

When using Allen-Bradley timers, which mnemonic status bit will act as an instantaneous contact?

a. DN

b. TT

c. EN

d. IN

c. EN

When the accumulated time is equal to the preset time, which mnemonic status bit in the Allen-Bradley timer will be true?

a. DN

b. TT

c. EN

d. IN

a. DN

When programming a Logix 5000 timer, what preset value would be entered to create a 23-minute timer?

23000

An Allen-Bradley off-delay timer (TOF) has been programmed for a delay time of 30 seconds. If the timer is enabled (true) for 15 seconds and then becomes disabled (false) for 45 seconds, show a timing chart for the enable (EN), timer timing (TT), and done (DN) status bits of the timer.

Drawing.

#1 What is the function of a PLC input interface module?

To accept signals from the machine or process devices and to convert them into signals that can be used by the controller

#2 What is the function of a PLC output interface module?

To convert controller signals into external signals that are used to control the machine or process

#3 With reference to a PLC:

What is a remote rack?

Why are remote racks used?

a) A rack that is located away from the processor module near the field devices

b) To minimize the amount of wiring required

#4 How does the processor identify the location of a specific input or output device?

By its address

#5 List the three basic elements of rack/slot-based addressing.

Type refers to an input or output

Slot refers to the physical location of the I/O module

Word and bit refers to the actual module terminal connection

#6 Compare bit level and word level addressing.

Bit level addressing specifies a discrete device that is connected to a specific terminal. Word level addressing specifies an analog device connected to a module that uses a word of information.