PLC 1 Flashcards
also referred to as
programmable controllers, are in the computer family.
Programmable Logic Controllers(PLCs)
monitors
inputs, makes decisions based on its program, and controls
outputs to automate a process or machine.
Programmable Logic Controllers(PLCs)
Parts of PLC
input modules or points, a Central Processing
Unit (CPU), and output modules or points.
input modules or points, a Central Processing
Unit (CPU), and output modules or points.
PLC parts
accepts a
variety of digital or analog signals from various field devices
(sensors) and converts them into a logic signal that can be used
by the CPU.
INPUT or INPUT modules or points
CPU
makes decisions and executes control
instructions based on program instructions in memory.
makes decisions and executes control
instructions based on program instructions in memory.
CPU
NPUT or INPUT modules or points
accepts a
variety of digital or analog signals from various field devices
(sensors) and converts them into a logic signal that can be used
by the CPU.
convert control instructions from the CPU into a digital
or analog signal that can be used to control various field devices
(actuators).
Output
modules
Output
modules
convert control instructions from the CPU into a digital
or analog signal that can be used to control various field devices
(actuators).
is used to input the desired
instructions. These instructions determine what the PLC will do
for a specific input.
Programming Device
Programming Device
is used to input the desired
instructions. These instructions determine what the PLC will do
for a specific input.
allows process
information to be displayed and new control parameters to be
entered.
An operator interface device
An operator interface device
allows process
information to be displayed and new control parameters to be
entered.
Prior to PLCs, what are the devices used to control the task done by PLC
RELAY controls or Contactor
RELAY controls or Contactor
devices used to control the task prior to PLCs
Hard-wiring
Method used for automating Inputs and outputs of a system through relay or contactor.Circuit diagrams had to be designed, electrical
components specified and installed, and wiring lists created.
Electricians would then wire the components necessary to
perform a specific task. If an error was made the wires had
to be reconnected correctly. A change in function or system
expansion required extensive component changes and rewiring.
Method used for automating Inputs and outputs of a system through relay or contactor.Circuit diagrams had to be designed, electrical
components specified and installed, and wiring lists created.
Electricians would then wire the components necessary to
perform a specific task. If an error was made the wires had
to be reconnected correctly. A change in function or system
expansion required extensive component changes and rewiring.
Hard Wiring
advantages of PLCs
Smaller physical size than hard-wire solutions.
* Easier and faster to make changes.
* PLCs have integrated diagnostics and override functions.
* Diagnostics are centrally available.
* Applications can be immediately documented.
* Applications can be duplicated faster and less expensively.
Samples of application of PLCs
smaller, stand-alone applications such as elevators, car washes,
or mixing machines. It can also be used on more complex
industrial applications such as bottling and packaging machines.
Characteristics of number systems
digits, base, weight.
information in the form of
On or Off conditions (1 or 0),
Binary digits
digits in terms of Decimal
0,1,2,3,4,5,6,7,8,9
Base or Radix in terms of Decimal
10
Weights in decimal
1, 10, 100, 1000 etc. (power of 10s)
Weights in decimal
Powers of base 2(1, 2, 4, 8, 16,…)
sensor
is a device that converts a physical condition into an
electrical signal for use by the PLC.
is a device that converts a physical condition into an
electrical signal for use by the PLC.
Sensor
Sensors are connected to
Input of PLC
convert an electrical signal from the PLC into a
physical condition. connected to the PLC output.
Actuator
Actuator
convert an electrical signal from the PLC into a
physical condition. connected to the PLC output.
Voltage input of PLC
24 VDC
analog input
is an input signal that has a continuous signal.
what inputs are those that may vary from 0 to 20 milliamps, 4 to 20
milliamps, or 0 to 10 volts.
analog input since they can vary
discrete output
an output that is either in an ON or OFF
condition.
Solenoids, contactor coils, and lamps are examples
of actuator devices connected to
discrete outputs.
Discrete
outputs may also be referred to as
Digital outputs
Examples of analog meter
speed, weight, and temperature.
speed, weight, and temperature.
Examples of analog meter
is a microprocessor system
that contains the system memory and is the PLC decision-
making unit.
The central processor unit
monitors the inputs and makes decisions
based on instructions held in the program memory.
CPU
performs relay, counting, timing, data comparison, and
sequential operations.
CPU
consists of one or more instructions that accomplish
a task.
Program
simply constructing a set of
instructions.
Programming a PLC
ladder logic, statement lists, or function block diagrams.
Different PLC programming methods
Different PLC programming methods
ladder logic, statement lists, or function block diagrams.
one programming language used
with PLCs.
Ladder logic (LAD)
uses components that resemble
elements used in a line diagram format to describe hard-wired
control.
Ladder Logic
represents the
power or energized conductor.
Left Vertical line
represents the neutral or return path of the circuit.
output element or instruction
represents the return path on a hard-wired
control line diagram, is omitted.
Right Vertical line
Ladder logic diagrams are read from
left-to-right, top-to-bottom.
are sometimes referred
to as networks.
Rungs
may have several control elements,
but only one output coil.
Network
provides another view of a set of instructions.
statement list (STL)
in STL he operation, what is to be done, is shown on
left
in STL The operand, the item to be operated on by the operation,
is shown on the
RIGHT
in STL A comparison between the statement
list shown
below
provide another view of a set of
instructions.
Function Block Diagrams (FBD)
in FBD, Functions are indicated by a
Rectangle
are shown
on the left-hand side of the rectangle
Inputs
are shown on
the right-hand side.
OUTPUTS
The PLC program is executed as part of a repetitive process
referred to as a
scan
A PLC scan starts with
CPU reading
the status of inputs.
The application program is executed using
the status of inputs.
Once the program is completed,
the
CPU performs internal diagnostics and communication tasks.
The scan cycle ends by
updating the outputs, then starts over.
any information in a form that a computer or PLC
can use.
Software
is the actual equipment. The PLC, the programming
device, and the connecting cable are examples of
Hardware
is memory where data can be
directly accessed at any address.
RAM (Random Access Memory)
Data can be written to and
read from
RAM (Random Access Memory)
is used as a temporary storage area and is volatile.
RAM (Random Access Memory)
the data stored in RAM will be
(____) if power is lost.
lost
is a type of memory that data can
be read from but not written to and This type of memory is used
to protect data or programs from accidental erasure.
Read Only Memory (ROM)
this memory type is nonvolatile. This means a user program will not lose
data during a loss of electrical power.
Read Only Memory (ROM)
(EPROM)
Erasable Programmable Read Only Memory
provides
some level of security against unauthorized or unwanted
changes in a program.
Erasable Programmable Read Only Memory
EPROMs are designed so that data
stored in them can be read, but not easily altered.
EPROM
can only be erased
with an ultraviolet light.
UVEPROMs (ultraviolet
erasable programmable read only memory)
memory), can only be erased
electronically.
EEPROM (electronically erasable
programmable read only memory),
user or application specific software burned into
EPROM and delivered as part of the hardware.gives
the PLC its basic functionality.
Firmware
