[PPT]PROGRAMMABLE LOGIC CONTROLLER
Control Systems Types
Programmable Logic Controllers
Distributed Control System
PC- Based Controls
Programmable Logic Controllers
Sequential logic solver
PID Calculations.
Advanced Subroutines
BIT Operations.
Data Transfer.
Text Handling.
Applications :
Machine controls, Packaging, Palletizing, Material handling, similar Sequential task as well as Process control
Advantages of PLC :
They are fast and designed for the rugged industrial environment.
They are attractive on Cost-Per-Point Basis.
These Devices are less Proprietary ( E.g.. Using Open Bus Interface.)
These Systems are upgraded to add more Intelligence and Capabilities with dedicated PID and Ethernet Modules.
Disadvantages of PLC :
PLC were Designed for Relay Logic Ladder and have Difficulty with some Smart Devices.
To maximize PLC performance and Flexibility, a number of Optional Modules must be added
Read more
[PPT]Programming PLCs using LADDER Logic
Review of Ladder Programming
Keyence PLC Ladder Builder
Example 1: Motor Control
Example 2: Drill Control
Example 3: Traffic Light
Ladder Logic Diagrams
Diagrams
Sequential Function Charts
Instruction ListFunction Block
Structured Text
High-Level Language
[PPT]Introduction to IEC1131-3 Ladder Diagram
Origins of Ladder Diagram
The Ladder Diagram (LD) programming language originated from the graphical representation used to design an electrical control system
Control decisions were made using relays
After a while Relays were replaced by logic circuits
Logic gates used to make control decisions
Finally CPUs were added to take over the function of the logic circuits
I/O Devices wired to buffer transistors
Control decisions accomplished through programming
Relay Logic representation (or LD) was developed to make program creation and maintenance easier
Computer based graphical representation of wiring diagrams that was easy to understand
Reduced training and support cost
What is a Rung?
A rung of ladder diagram code can contain both input and output instructions
Input instructions perform a comparison or test and set the rung state based on the outcome
Normally left justified on the rung
Output instructions examine the rung state and execute some operation or function
In some cases output instructions can set the rung state
Normally right justified on the rung
Read more
Programmable Logic Controllers-Fourth Edition by W. Bolton
This chapter is an introduction to the programmable logic controller, its
general function, hardware forms and internal architecture. This overview
is followed up by more detailed discussion in the following chapters.
What type of task might a control system have? It might be required to
control a sequence of events or maintain some variable constant or follow
some prescribed change. For example, the control system for an automatic
drilling machine (Figure 1.1(a)) might be required to start lowering the
drill when the workpiece is in position, start drilling when the drill reaches
the workpiece, stop drilling when the drill has produced the required
depth of hole, retract the drill and then switch off and wait for the next
workpiece to be put in position before repeating the operation. Another
control system (Figure 1.1(b)) might be used to control the number of
items moving along a conveyor belt and direct them into a packing case.
The inputs to such control systems might be from switches being closed or
opened, e.g. the presence of the workpiece might be indicated by it
moving against a switch and closing it, or other sensors such as those used
for temperature or flow rates. The controller might be required to run a
motor to move an object to some position, or to turn a valve, or perhaps a
heater, on or off.
Read more
PROGRAMMABLE CONTROLLERS HAND BOOK – L.A.BRYAN
Programmable logic controllers, also called programmable controllers or
PLCs, are solid-state members of the computer family, using integrated
circuits instead of electromechanical devices to implement control functions.
They are capable of storing instructions, such as sequencing, timing,
counting, arithmetic, data manipulation, and communication, to control
industrial machines and processes. Figure 1-1 illustrates a conceptual
diagram of a PLC application
Programmable controllers have many definitions. However, PLCs can be
thought of in simple terms as industrial computers with specially designed
architecture in both their central units (the PLC itself) and their interfacing
circuitry to field devices (input/output connections to the real world).
As you will see throughout this book, programmable logic controllers are
mature industrial controllers with their design roots based on the principles of
simplicity and practical application.
