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Chapter 1
PLCs An Overview
TRUE/FALSE
1. PLCs were originally designed as replacements for relay logic.
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2. A PLC is capable of performing only relay switching tasks.
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3. The term module refers to a replaceable electronic subassembly.
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4. On micro PLC systems, the power supply module can also be used to power field devices.
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5.
Connection to PLC field devices are hard-wired.
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6. Any change to a PLC program normally involves some change in wiring as well.
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7. It is not possible for a PLC to detect objects that spend only a fraction of a second in front of a sensor.
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8. PLCs operate in real-time.
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9. Field devices are user supplied devices that provide information to the PLC or perform PLC tasks.
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10. The input module of the PLC is responsible for performing logical operations.
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11. An instruction is a command that will cause a PLC to perform a certain predetermined operation.
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12. Normally a PLC cannot communicate with other controllers or computer equipment.
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13. A proprietary control system allows the system to be connected easily to devices and programs made
by other manufacturers.
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14. A PLC uses an optical isolator to electrically isolate the internal components from the input and output
terminals.
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MULTIPLE CHOICE
1. A _______ PLC application involves one PLC controlling one process.
a. multitask
c. single-ended
b. control-management
d. data acquisition
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2. The ________ for a particular PLC lists all instructions along with a short description of their
operation.
a. software
c. instruction set
b. hardware
d. program
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3. A __________ is the most commonly used programming device for PLCs.
a. personal computer
c. operator interface
b. hand-held programmer
d. processor
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4. In which module of the PLC is the decision making performed?
a. processor module
c. output module
b. input module
d. power supply module
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5. Which of the following is a factor effecting the memory size needed for a PLC installation?
a. voltage rating of field devices
c. current rating of field devices
b. number of I/O points
d. type of programming device
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6. Additional optional PLC components are often available, including:
a. operator interface devices
c. network interfaces
b. communication adaptors
d. all of these
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7. Which of the following is a task that a PLC is NOT capable of performing?
a. timing
c. directly switching large motors
b. counting
d. comparing
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8. The main advantage of fixed I/O is:
a. lower cost
b. increased flexibility
c. greater selection of modules
d. faster replacement of I/O modules
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9. The processor section of the PLC is where:
a. the program is stored
b. the inputs are connected
c. the outputs are connected
d. the sensors are located
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10. The input interface module:
a. allows the user to input a program
b. connects the CPU to signals from the
process
c. allows the CPU to input messages to a
CRT screen
d. provides inputs to field devices
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11. The output interface module:
a. is always a CRT screen device
b. allows the program in memory to be
output to the CPU
c. connects the CPU to the process and
produces control signals
d. all of these
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12. A PLC has no:
a. keyboard
b. disk drive
c. monitor
d. all of these
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13. Which of the following is an advantage of personal-computer-based control systems?
a. Lower initial cost
b. More proprietary
c. Ease of programming
d. All of these
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14. In general, Micro PLCs can connect up to about ______ I/O points.
a. 6
c. 18
b. 12
d. 32
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15. A PLC that uses 8-bit words and has a 6K word capacity has ______ bits of storage capacity.
a. 8,000
c. 49,152
b. 42,000
d. 52,460
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COMPLETION
1. CPU is an abbreviation for _________ _____________ _____________.
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2. I/O is an abbreviation for _________ and ________ modules.
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3. Modifying relay type process control circuits usually involves changing the circuit ___________.
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4. The ________ module of the PLC connects to field devices such as pilot lights, motor starters, and
solenoids.
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5. The ______ time is the time required for one complete execution of the user program.
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6. Categorization of PLC size is primarily based on the number of _______ points.
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7. A programmable controller is basically a specialized _________ used to control machines and process
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8. Typically, the numbers associated with a PLC instruction represents the instruction's _________.
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9. ________ logic programming is a method of programming a PLC that resembles a relay schematic
diagram.
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10. The ________ is a selected method of operation such as RUN, TEST, or PROGRAM setting of the
processor.
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11. _______ I/O is typical of small PLCs that come all in one package with no separate, removable
modules.
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12. Normally, when a field device contact connected to the input module closes, the associated address is
set to logic ____.
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13. Compact ___________ programming devices are frequently used on the factory floor for
troubleshooting equipment.
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