List 3 basic components of any PLC control system.
*Input devices
*Controller
*Output devices
The diagnostic function of a PLC facilitates what?
Maintenance, automatic alarming and system monitoring.
List a few of the industries and processes that rely on PLC control.
Chemical and petrochemical, automiobile manufacturing, machining, mining, lumber, pulp and paper, glass and film, food and beverage production, metal smelting, power production and mail sorting.
PLC's are usually selected by?
number of input and output points they can service. Large systems can have greater than 120 000 I/O's and, as the systems become larger, the programming, memory and communication capabilities also increase.
What are some of the advantages of using a PLC over a relay control system?
*Lower overall cost,
*programmability
*reliability
*they are easily expandable.
PLC systems are physically(smaller/larger) than functionally equivalent relay panels and consume(less/more)energy?
Smaller, Less.
PLC programs can be changed while the processor is running. TRUE or FALSE.
TRUE.
The major hardware components of a modular PLC system are the:
*Backplane
*power supply
*processor(CPU) and
*input/output(I/O) modules.
and the programming device is also required.
Backplane provides mounting slots for the?
Power supply, a processor, input modules, output modules and various specialty modules.
What does the processor do?
The processor is the brain of the PLC that governs system activities regarding receiving, analyzing, processing and transmitting data.
The primary function of a PLC processors are to:
*read and store the status of all the input devices,
*execute the user program by solving the program's logic
*update the status of all the outputs.
List two types of memory used by the processor.
Volatile memory and non Volatile memory.
*Non Volatile memory will retain data and programs after the electrical power source has been removed. Non volatile memory is generally considered permanent.
*Volatile memory is cleared of all data if it loses its
What is Ram? And what are it's characteristics?
Random access memory is designed so information is easily stored and retrieved. Most ram is volatile memory.
What is ROM and it's characteristics?
READ ONLY MEMORY is non-volatile and is designed to permanently store data and programs. The information may be examined or read but not altered or written to by a user.
What is EEPROM and it's characteristics?
Electrically erased, programmable memory. It is integrated in to circuit memory that is considered non-volatile, but can be reprogrammed using a PLC programming device.
In order to reduce wiring and installation costs, remote I/O modules may be installed. TRUE or FALSE
TRUE.
What is a data highway for a PLC system?
local area network(LAN) cabling that connects a number of PLC's, or PLC's and personal computers, together allowing them to exchange programs and data.
List the major comopnents of a modular PLC system.
*backplane
*power supply
*processor
*input/output modules
What form of the PLC does the CPU form part of?
Processor.
Name 3 types of memory used by a PLC.
*Ram
*Rom
*Eeprom.
What does an input module do?
receives signals from sensing devices
Input and output devices are one of two types, what are they?
discrete or analog.
*discrete devices are either on or off.
*Analog devices operate over a range of values.
An example of an analog input signal is:
*current @ 4-20ma
*voltage @ 0-10v
The following analog input signals could be used to control the speed of a motor using a VFD.
*0-10v signal from a PLC output module
*4-20ma signal from a level transmitter
*the output from an analog temperature transmitter.
The most common type of cable used for analog cables of a PLC is shielded twisted pair(STP). The conductor size may be as?
as small as #22AWG because the current levels are so small.
A thermal overload contact would be an example of a discrete device. TRUE or FALSE
True
A pressure transmitter that provides a proportional signal for 0-200PSI is an example of a discrete device. true or false
False, this is an analog device.
Boolean algebra expression for?
the result of wiring an AND gate and an OR gate in this configuration--> Q=(A+B)C
There are five main types of languages used for programming PLCs; three are graphic-based and two are text-based. The three graphic based languages are?
*Ladder Diagram.
*function block diagram.
*sequential function chart.
In PLC programming the two text-based languages are:
*structured text
*instruction list.
In order for an AND gate to work, both inputs must be #1. True or False.
True.
In an or gate if one or the other are #1 or both are #1 then they will be true(has a voltage). True or False.
True.
A not gate output is true if the input is false. True or False.
True
What is the most common programming language for PLC's sued in North America?
Ladder Logic.
For what application is sequential functional chart programming most suitable?
Large process control where several complex functions take place in sequence.
Most PLCs use text based languages. True or False.
False, most use graphic based Languages.
What provides the interface between a limit switch(discreet device) and the processor(CPU) in a PLC?
the input card.
What is the purpose of the on board battery in the PLC processor?
to maintain the RAM in the processor
In the PLC 5 processor the "done bit" is "set" when an on-delay(TON) timer has timed out.True or False.
True.
Timers used in PLC programs can be used for?
*operating internal coils.
*operating external coils.
*switching a programmed output.
Hardware means?
mechanical, electrical, and electronic devices.
The "basic" components in any control system are:
*input devices,
*a controller
*output devices
On advantage to using a PLC is?
they are easily reprogrammed if requirements change.
The third digit of a PLC 5 address, used for an open contact within a program is?
The module group number. I:00O/1
The 4th and 5th digits of a PLC 5 address for a closed contact within a program is the?
Bit address. I:000/1<----this one
The first two digits of a PLC 5 address is the?
Rack address. I:OO0/1
The voltage required from the output modules of programmable controllers to the magnetic motor starters(field windings) depends on the?
voltage rating of the coil in the magnetic starter.
Counter can be used for?
*operating internal coils
*operating external coils(starters, relays, solenoid valves etc.)
*switching a programmed output "on"
*switching a programmed output "off
When using 8 point 120v output cards with our Allen Bradley PLC 5 processors:
the maximum current for each output is 1.5 Amps.
What is a bit?
One binary digit. The smallest unit of binary information. A bit can have a value of "1" or "0".
What is a "word"?
The unit number of binary bits used by the CPU when performing an instruction, or operating on data. A word is usually composed of a fixed number of bits. One PLC word=16 data bits.
What is a byte?
8 consecutive bits.
What is a Chassis in PLCs?
A hardware assembly which contains the I/O modules, adapter modules, processor modules, power supplies and processors.
Field wiring arms are used to?
connect field wiring to input/output modules, but allow modules to be replaced without re-wiring.
The Cpu must be installed on the left side of the chassis?True or False.
True.
Where is the backplane located?
in the back of the chassis.
The CPU is connected directly to field devices. True or False.
False
There are three types of numbering systems used in a PLC. What are they?
*Decimal
*Binary
*Octal
What is a nibble?
A group of 4 bits handled by the processor.
Each digit of a binary number is called a?
Bit.
The octal # system goes from 1-8 true or false?
False, it goes from 0-7
The processor of a PLC provides low voltage protection?True or False.
False, the program provides low voltage protection.
Field wiring arms must have wiring disconnected before a module can be removed. T or F
False.
the maximum decimal value that can be stored is?
+32,767 or -32,767
The output module can supply _____ amps per output with a maximum of _____ amps per module.
1.5 and 6
The input modules provide electrical isolation between the A.C. input and the electronic logic circuits by using a?
optoisolator.