Fundamentos plc
Páginas: 13 (3121 palabras)
Publicado: 21 de marzo de 2012
A PLC Primer
T ABLE
OF
C ONTENTS
pg 3 pg 4 pg 5 pg 7 pg 10 pg 13 pg 14 pg 15
What Is a PLC? Why Use PLCs? But What Exactly Is a PLC? A Little More About Inputs and Outputs And a Little More About the Control Program So How Does a PLC Keep All This Straight? To Sum It All Up Want To Learn More?
Industrialtext & Video Company
www.industrialtext.com
1-800-752-8398
©1999 byIndustrial Text & Video Company. All rights reserved.
A PLC Primer
WHAT IS A PLC?
A programmable logic controller, also called a PLC or programmable controller, is a computer-type device used to control equipment in an industrial facility. The kinds of equipment that PLCs can control are as varied as industrial facilities themselves. Conveyor systems, food processing machinery, autoassembly lines…you name it and there’s probably a PLC out there controlling it. In a traditional industrial control system, all control devices are wired directly to each other according to how the system is supposed to operate. In a PLC system, however, the PLC replaces the wiring between the devices. Thus, instead of being wired directly to each other, all equipment is wired to the PLC. Then, thecontrol program inside the PLC provides the “wiring” connection between the devices. The control program is the computer program stored in the PLC’s memory that tells the PLC what’s supposed to be going on in the system. The use of a PLC to provide the wiring connections between system devices is called softwiring.
E XAMPLE
Let’s say that a push button is supposed to control the operation of amotor. In a traditional control system, the push button would be wired directly to the motor. In a PLC system, however, both the push button and the motor would be wired to the PLC instead. Then, the PLC’s control program would complete the electrical circuit between the two, allowing the button to control the motor.
In a traditional system, all control devices are wired directly to each other……In a PLC system, all control devices are wired to the PLC.
PLC
Industrial Text & Video Company
1-800-752-8398
www.industrialtext.com
3
A PLC Primer
WHY USE PLCS?
The softwiring advantage provided by programmable controllers is tremendous. In fact, it is one of the most important features of PLCs. Softwiring makes changes in the control system easy and cheap. If youwant a device in a PLC system to behave differently or to control a different process element, all you have to do is change the control program. In a traditional system, making this type of change would involve physically changing the wiring between the devices, a costly and time-consuming endeavor.
E XAMPLE
Let’s say that two push buttons, PB1 and PB2, are connected to a PLC. Two pilot lights,PL1 and PL2, are also connected to the PLC. The way these devices are connected now pressing push button PB1 turns on pilot light PL1 and pressing push button PB2 turns on pilot light PL2. Let’s say that you want to change this around so that PB1 controls PL2 and PB2 controls PL1. In a traditional system, you would have to rewire the circuit so that the wiring from the first push button goes to thesecond pilot light and vice versa. However, because these devices are connected to a PLC, making this change is as simple as making a small change in the control program.
In addition to the programming flexibility we just mentioned, PLCs offer other advantages over traditional control systems. These advantages include: • high reliability • small space requirements • computing capabilities •reduced costs • ability to withstand harsh environments • expandability
Industrial Text & Video Company
1-800-752-8398
www.industrialtext.com
4
A PLC Primer
BUT WHAT EXACTLY IS A PLC?
A PLC basically consists of two elements: • the central processing unit • the input/output system
The Central Processing Unit
The central processing unit (CPU) is the part of a programmable...
T ABLE
OF
C ONTENTS
pg 3 pg 4 pg 5 pg 7 pg 10 pg 13 pg 14 pg 15
What Is a PLC? Why Use PLCs? But What Exactly Is a PLC? A Little More About Inputs and Outputs And a Little More About the Control Program So How Does a PLC Keep All This Straight? To Sum It All Up Want To Learn More?
Industrialtext & Video Company
www.industrialtext.com
1-800-752-8398
©1999 byIndustrial Text & Video Company. All rights reserved.
A PLC Primer
WHAT IS A PLC?
A programmable logic controller, also called a PLC or programmable controller, is a computer-type device used to control equipment in an industrial facility. The kinds of equipment that PLCs can control are as varied as industrial facilities themselves. Conveyor systems, food processing machinery, autoassembly lines…you name it and there’s probably a PLC out there controlling it. In a traditional industrial control system, all control devices are wired directly to each other according to how the system is supposed to operate. In a PLC system, however, the PLC replaces the wiring between the devices. Thus, instead of being wired directly to each other, all equipment is wired to the PLC. Then, thecontrol program inside the PLC provides the “wiring” connection between the devices. The control program is the computer program stored in the PLC’s memory that tells the PLC what’s supposed to be going on in the system. The use of a PLC to provide the wiring connections between system devices is called softwiring.
E XAMPLE
Let’s say that a push button is supposed to control the operation of amotor. In a traditional control system, the push button would be wired directly to the motor. In a PLC system, however, both the push button and the motor would be wired to the PLC instead. Then, the PLC’s control program would complete the electrical circuit between the two, allowing the button to control the motor.
In a traditional system, all control devices are wired directly to each other……In a PLC system, all control devices are wired to the PLC.
PLC
Industrial Text & Video Company
1-800-752-8398
www.industrialtext.com
3
A PLC Primer
WHY USE PLCS?
The softwiring advantage provided by programmable controllers is tremendous. In fact, it is one of the most important features of PLCs. Softwiring makes changes in the control system easy and cheap. If youwant a device in a PLC system to behave differently or to control a different process element, all you have to do is change the control program. In a traditional system, making this type of change would involve physically changing the wiring between the devices, a costly and time-consuming endeavor.
E XAMPLE
Let’s say that two push buttons, PB1 and PB2, are connected to a PLC. Two pilot lights,PL1 and PL2, are also connected to the PLC. The way these devices are connected now pressing push button PB1 turns on pilot light PL1 and pressing push button PB2 turns on pilot light PL2. Let’s say that you want to change this around so that PB1 controls PL2 and PB2 controls PL1. In a traditional system, you would have to rewire the circuit so that the wiring from the first push button goes to thesecond pilot light and vice versa. However, because these devices are connected to a PLC, making this change is as simple as making a small change in the control program.
In addition to the programming flexibility we just mentioned, PLCs offer other advantages over traditional control systems. These advantages include: • high reliability • small space requirements • computing capabilities •reduced costs • ability to withstand harsh environments • expandability
Industrial Text & Video Company
1-800-752-8398
www.industrialtext.com
4
A PLC Primer
BUT WHAT EXACTLY IS A PLC?
A PLC basically consists of two elements: • the central processing unit • the input/output system
The Central Processing Unit
The central processing unit (CPU) is the part of a programmable...
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