,Answers to Chapter 1 Review Problems
, Answers to Chapter 1 Review Questions
1. A programmable logic controller (PLC) is a specialized computer used to control machines
and process.
2. Counting, calculating, comparing and the processing of analog signals.
3. Increased Reliability
More Flexibility
Lower Cost
Communications Capability
Faster Response Time
Easier to Troubleshoot
4. An open architecture design allows the system to be connected easily to devices and
programs made by other manufacturers. A proprietary architecture makes it more difficult to
connect to another manufacturer’s system.
5. Fixed and modular configurations
6. The I/O modules plug into a rack. When a module is slid into the rack, it makes a connection
with a series of contacts called the backplane. The PLC processor is also connected to the
backplane and, therefore, can communicate with all modules in the rack.
7. a) Accepts input data from sensing devices, executes the stored user program from memory,
and sends appropriate output commands to control devices.
b) Forms the interface by which field devices are connected to the controller.
c) Used to enter the desired program into the memory of the processor.
d) Supplies DC power to other modules.
8. Laptop computers and personal computers
9. A program is a user-developed series of instructions that directs the PLC to execute actions.
A programming language provides rules for combining the instructions so that they produce
the desired actions.
10. Relay ladder logic (RLL) is the standard programming language used with PLCs.
11. a) When the pressure reaches the preset value
b) When the temperature reaches the preset value
c) In series
d) If the pressure switch and temperature switch contacts close or if the pushbutton contacts
close.
e) 1) 1.0 VAC
2) 0 VAC
, 3) 120 VAC
12. A programmable logic controller operates in real time in that an event taking place in the
field will result in an operation or output taking place.
13. a) Instructions
b) Addresses
c) Temperature switch
d) Motor starter coil
e) If contacts I/1 and I/2 are closed
If contact I/3 is closed
f) Inputs are examined, and their status is recorded in the controller’s memory. The ladder
diagram is evaluated. The output is set to 0 or 1 according to whether or not a complete
current path can be traced from left to right.
14. Relay system is changed by changing the wiring. PLC system is changed by changing the
program.
15. a) Unlike personal computers, the PLC comes with its program language built into its
memory and has no permanently attached keyboard, CD drive, or monitor.
b) Unlike personal computers, PLCs are designed to operate with wide ranges of ambient
temperature and humidity.
c) Unlike personal computers, the PLC is programmed in relay ladder logic or other easily
learned languages.
d) PLCs execute a single program in a sequential order, while computers execute several
programs or tasks simultaneously in any order.
16. Software that allows the user to write and document a PLC program. Software that allows the
user to monitor and control a PLC program.
17. A PAC is a device that combines PLC-style control and ruggedness with PC functionality.
18. a) Functionality
b) Number of inputs and outputs
c) Cost
d) Physical size
19. A single-ended application involves one PLC controlling one process. A multitask
application involves one PLC controlling several processes. A control management
application involves one PLC controlling several others.
20. 16 × 8 × 1024 = 131,072
21. Number of I/O points, size of control program, data-collecting requirements, supervisory
junctions required, and future expansion.
, Answers to Chapter 1 Review Questions
1. A programmable logic controller (PLC) is a specialized computer used to control machines
and process.
2. Counting, calculating, comparing and the processing of analog signals.
3. Increased Reliability
More Flexibility
Lower Cost
Communications Capability
Faster Response Time
Easier to Troubleshoot
4. An open architecture design allows the system to be connected easily to devices and
programs made by other manufacturers. A proprietary architecture makes it more difficult to
connect to another manufacturer’s system.
5. Fixed and modular configurations
6. The I/O modules plug into a rack. When a module is slid into the rack, it makes a connection
with a series of contacts called the backplane. The PLC processor is also connected to the
backplane and, therefore, can communicate with all modules in the rack.
7. a) Accepts input data from sensing devices, executes the stored user program from memory,
and sends appropriate output commands to control devices.
b) Forms the interface by which field devices are connected to the controller.
c) Used to enter the desired program into the memory of the processor.
d) Supplies DC power to other modules.
8. Laptop computers and personal computers
9. A program is a user-developed series of instructions that directs the PLC to execute actions.
A programming language provides rules for combining the instructions so that they produce
the desired actions.
10. Relay ladder logic (RLL) is the standard programming language used with PLCs.
11. a) When the pressure reaches the preset value
b) When the temperature reaches the preset value
c) In series
d) If the pressure switch and temperature switch contacts close or if the pushbutton contacts
close.
e) 1) 1.0 VAC
2) 0 VAC
, 3) 120 VAC
12. A programmable logic controller operates in real time in that an event taking place in the
field will result in an operation or output taking place.
13. a) Instructions
b) Addresses
c) Temperature switch
d) Motor starter coil
e) If contacts I/1 and I/2 are closed
If contact I/3 is closed
f) Inputs are examined, and their status is recorded in the controller’s memory. The ladder
diagram is evaluated. The output is set to 0 or 1 according to whether or not a complete
current path can be traced from left to right.
14. Relay system is changed by changing the wiring. PLC system is changed by changing the
program.
15. a) Unlike personal computers, the PLC comes with its program language built into its
memory and has no permanently attached keyboard, CD drive, or monitor.
b) Unlike personal computers, PLCs are designed to operate with wide ranges of ambient
temperature and humidity.
c) Unlike personal computers, the PLC is programmed in relay ladder logic or other easily
learned languages.
d) PLCs execute a single program in a sequential order, while computers execute several
programs or tasks simultaneously in any order.
16. Software that allows the user to write and document a PLC program. Software that allows the
user to monitor and control a PLC program.
17. A PAC is a device that combines PLC-style control and ruggedness with PC functionality.
18. a) Functionality
b) Number of inputs and outputs
c) Cost
d) Physical size
19. A single-ended application involves one PLC controlling one process. A multitask
application involves one PLC controlling several processes. A control management
application involves one PLC controlling several others.
20. 16 × 8 × 1024 = 131,072
21. Number of I/O points, size of control program, data-collecting requirements, supervisory
junctions required, and future expansion.
