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Profil Laboratorium Sistem Otomasi dan Robotika Teknik Industri Universitas Trunojoyo
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Programmable Logic Controllers (PLC)
What is a
PLC?
In this module you will be introduced to a controller called a PLC. The initials PLC stand for programmable logic controller. A PLC is often used as the "brain" in a wide range of modern controlled systems.
A PLC is essentially a low level computer capable of interfacing with field instrumentation to read input data and control output data. PLCs can generally be programmed from a PC, typically using ladder logic, sequential function charts, and/or structured text.
In some cases, PLCs are connected to a central control computer. Each PLC works independently to control its assignment while feeding information back to the central computer.
PLC's form the basis of what is known as "distributed control". Just as computer systems have migrated away from large mainframe computers, control systems have distributed the "decision making" to PLCs (smart control nodes).
In this module you will be introduced to a controller called a PLC. The initials PLC stand for programmable logic controller. A PLC is often used as the "brain" in a wide range of modern controlled systems.
A PLC is essentially a low level computer capable of interfacing with field instrumentation to read input data and control output data. PLCs can generally be programmed from a PC, typically using ladder logic, sequential function charts, and/or structured text.
In some cases, PLCs are connected to a central control computer. Each PLC works independently to control its assignment while feeding information back to the central computer.
PLC's form the basis of what is known as "distributed control". Just as computer systems have migrated away from large mainframe computers, control systems have distributed the "decision making" to PLCs (smart control nodes).
How Does It
Work?
Programmable logic controllers take real world inputs from sensors and convert these inputs into electrical signals. These signals update an input table in the "computer".
An I/O board provides the communucation link between the processor and the sensor. The input signals are used to determine which outputs are to be turned on and off.
The PLC in the Modern Industrial World
The PLC is
commonplace in today's industrial world. For example, because of their memory
input control capabilities, many elements of an assembly plant utilize PLC's.
In fact, just about every existing automation line is controlled by a PLC.
These small units are microprocessor-based and contain non-volatile memory locations (memory that maintains data storage when power is removed) that contain specific instructions programmed by a user for a given application. A PLC can control a wastewater pumping facility for the utility department in a city, while another PLC in a nearby factory controls a smelting furnace.
PLCs are used to control processes that need feedback in order to create consistency. For example, in the Janesville WI, General Motors Truck Facility, programmable logic controllers are used in the body shop to interface with robots, sealing equipment, and automated hard tooling that welds the sheet-metal body of a Suburban Utility Vehicle together.
These small units are microprocessor-based and contain non-volatile memory locations (memory that maintains data storage when power is removed) that contain specific instructions programmed by a user for a given application. A PLC can control a wastewater pumping facility for the utility department in a city, while another PLC in a nearby factory controls a smelting furnace.
PLCs are used to control processes that need feedback in order to create consistency. For example, in the Janesville WI, General Motors Truck Facility, programmable logic controllers are used in the body shop to interface with robots, sealing equipment, and automated hard tooling that welds the sheet-metal body of a Suburban Utility Vehicle together.
- Hard
Welding Automation
- Flexible
Manufacturing Systems
- Sealing
Applications
- Fluid
Fill Systems
- Facility
Monitoring Systems
Hardware Tasks
The following tasks require the use
of hardware.
If you have access to the PLC Trainer System with the Allen-Bradley SLC 500 PLC controller, click Start A/B SLC 500 Hardware Tasks below.
If you have access to the PLC Trainer System with the Allen-Bradley SLC 500 PLC controller, click Start A/B SLC 500 Hardware Tasks below.
If you have
access to the PLC Trainer System with the MicroLogix PLC controller,
click Start MicroLogix Hardware Tasks below.
If you do not have access to hardware, click Skip Hardware Tasks below.
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Safety Guidelines
Safety precautions in the PLC
environment serve to protect the human operators as well as the PLC equipment.
Always use caution when working with the PLCLine system to avoid personal
injury and damage to equipment.
All necessary hardware installation and wiring connections are to be performed by the laboratory instructor or system manager.
Be sure to heed the following safety guidelines:
All necessary hardware installation and wiring connections are to be performed by the laboratory instructor or system manager.
Be sure to heed the following safety guidelines:
- Position
PLCLine on a stable table. Make sure the PLCLine is placed on the table at
least 18 inches away from the table edges (in all four directions).
- All necessary hardware installation and wiring connections are to be performed by the laboratory instructor or system manager.
- Make
sure the power supply and the Allen Bradley PLC are connected to the rated
power supply.
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- Ensure
that 24VDC is not shorted to ground when connecting wires. Doing so will blow
the 24V/4A fuse. It is strongly recommended that a circuit diagram be prepared
before making an actual connection.
- Do
not touch or tamper with the DC motor unit, especially when it is in motion.
- Do
not tamper with the solenoid or limit switch units.
- To
immediately halt all system operation, switch OFF the power supply.
- Make
sure hands, hair and clothing are securely away from the motor working area.
- Maintain a clean work area at all
times.
- Keep
food and drink away from the workcell.
- Always
read the directions completely before doing a task.
- If
you are unsure of the operation of a system, talk to your instructor before
operating the equipment.
Inputs and Outputs
What are
Inputs and Outputs?
In the following activity, you will activate and use a PLC to control a number of devices. These devices can be divided into two main categories: input and output devices.
In the following activity, you will activate and use a PLC to control a number of devices. These devices can be divided into two main categories: input and output devices.
- Input
devices transmit data to the PLC. The status of the input devices reflects the
status of the controlled system or an operating requirement. The PLC constantly
monitors the status of these devices and checks it with a pre-defined set of
instructions.
- Output
devices receive activation instructions from the PLC. The status of the
output devices is determined by the status of the input devices and the control
instructions.
Input and Output
Devices
As you have already learned, programmable logic controllers control real world inputs and outputs in order to automate a process. Move your mouse over the image to see some input and output devices. Input and output devices include:
As you have already learned, programmable logic controllers control real world inputs and outputs in order to automate a process. Move your mouse over the image to see some input and output devices. Input and output devices include:
- Input Devices:
- Proximity Switches
- Flow Meters
- Limit Switches
- Output Devices:
- Solenoid
Valve
- Electromagnetic
Relay
- Motor
Starter
- Pressure
Gauges
- Horn
fitted in a car
Real-World
Example
Observe the example of a PLC-controlled level control system. A float is fitted on a tank at the level marked as 2. The float is an input device that is used as a level sensor. By controlling an on/off valve that serves as an output device, the user can control the water level.
The control instructions are stored in the PLC's memory. The PLC constantly receives an input signal (in this case, the water level). The PLC controls the output device (valve) according to the input (water level) and the instructions programmed in its memory.
Observe the example of a PLC-controlled level control system. A float is fitted on a tank at the level marked as 2. The float is an input device that is used as a level sensor. By controlling an on/off valve that serves as an output device, the user can control the water level.
The control instructions are stored in the PLC's memory. The PLC constantly receives an input signal (in this case, the water level). The PLC controls the output device (valve) according to the input (water level) and the instructions programmed in its memory.
Discrete and
Analog
I/O devices refer to the data read and written by the programmable controller.
There are two types of input and output:
Discrete
I/O consists of data represented by 1s and 0s. Discrete I/O systems are
used to control systems that can be in only one of two states, such as an ON or OFF state for a motor or a lamp.
Analog
I/O uses a number of bits to represent an integer value. For example, the pressure in a pneumatic system could be any
value between 0 and the highest integer value available on a particular
pressure gauge's scale.
Discrete input signals are usually used to determine if a certain event has happened (for example, the piston is fully extended or the pressure is above 3 bars). Discrete output devices are used to control elements that can be only in one out of two possible states.
You will learn more about this concept in the next module.
I/O devices refer to the data read and written by the programmable controller.
There are two types of input and output:
Discrete
I/O consists of data represented by 1s and 0s. Discrete I/O systems are
used to control systems that can be in only one of two states, such as an ON or OFF state for a motor or a lamp.Analog
I/O uses a number of bits to represent an integer value. For example, the pressure in a pneumatic system could be any
value between 0 and the highest integer value available on a particular
pressure gauge's scale. Discrete input signals are usually used to determine if a certain event has happened (for example, the piston is fully extended or the pressure is above 3 bars). Discrete output devices are used to control elements that can be only in one out of two possible states.
You will learn more about this concept in the next module.
Introduction
to Ladder Logic
In this module, you will use a virtual PLC and input devices to control output devices. You will program a virtual PLC using ladder logic programming language, a programming language typically used in PLC programming.
Throughout this module, you will learn basic commands in the ladder logic programming language. You will then program ladder diagrams using those commands to control various industrial-type control systems. This graphical language closely resembles electrical relay logic diagrams.
In this module, you will use a virtual PLC and input devices to control output devices. You will program a virtual PLC using ladder logic programming language, a programming language typically used in PLC programming.
Throughout this module, you will learn basic commands in the ladder logic programming language. You will then program ladder diagrams using those commands to control various industrial-type control systems. This graphical language closely resembles electrical relay logic diagrams.
Activity 1: Getting Started
In this
activity you will learn about programmable logic controllers (PLC) and their
use in today's modern industrial world. You will experiment with a Virtual
Input/Output panel to learn about the difference between input and output
components.
This activity includes the following topics:
This activity includes the following topics:
- Programable Logic Controllers
- Inputs and Outputs
OBJECTIVES
In this activity you will accomplish the following:
- Define
the term programmable logic controller.
- Define
the terms input and output.
- Learn
about typical uses of PLCs in industry and daily life.
- Distinguish
between discrete and analog inputs and outputs.
- Determine whether devices are input or output.
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