OMRON C500-TU001 3G2A5-TU001 PLC PLC

OMRON C500-TU001 3G2A5-TU001 PLC PLC

C500 Programmable Controller

This section provides general information about Programmable Controllers

(Systems) and how they fit into a Control System.

A Control System is the electronic equipment needed to control a particular

process. It may include everything from a process control computer, if one is

used, to the factory computer, down through the PCs (and there may be

many of them networked together), and then on down through the network to

the control components: the switches, stepping motors, solenoids, and sen

sors which monitor and control the mechanical operations

A Control System can involve very large applications where many different

models of PC are networked together or it could be an application as small

as a single PC controlling a single output device

In the typical Control System example shown above, a PC controls the move

ment of the workpiece bed across two horizontal axes using Limit Switches

and Servomotors to monitor and control movement.

The PC is the part of the Control System that directly controls the manufac

turing process. According to the program stored in its memory, the PC ac

cepts data from the input devices connected to it, and uses this data to moni

tor the controlled system. When the program calls for some action to take

place, the PC sends data to the output devices connected to it to cause that

action to take place. The PC may be used to control a simple, repetitive task,

or it may be connected to other PCs, or to a host computer in order to inte

grate the control of a complex process

Input Devices

PCs can receive input from either automated or manual devices. The PC

could receive data from the user via a pushbutton switch, keyboard, or simi

lar device. Automated input could come from a variety of devices: micro

switches, timers, encoders, photosensors, and so on. Some devices, like the

Limit Switch shown below, turn ON or OFF when the equipment actually

makes contact with them. Other devices, like the Photoelectric Switch and

Proximity Switch shown below, use other means, such as light or inductance,

in order to get information about the equipment being monitored

Output Devices

Proximity Switch

Limit Switch

A PC can output to a myriad of devices for use in automated control. Almost

anything that you can think of could be controlled (perhaps indirectly) by a

PC. Some of the most common devices are motors, Solenoids, Servomotors,

Stepping Motors, valves, switches, indicator lights, buzzers, and alarms.

Some of these output devices, such as the motors, Solenoids, Servomotors,

Stepping Motors, and valves, affect the controlled system directly. Others,

such as the indicator lights, buzzers, and alarms, provide output to notify per

sonnel

PCs operate by monitoring input signals and providing output signals. When

changes are detected in the signals, the PC reacts, through the user-pro

grammed internal logic, to produce output signals. The PC continually cycles

the program in its memory to achieve this control

A program for your applications must be designed, and stored in the PC. This

program is then executed as part of the cycle of internal operations of the

PC.

When a PC operates, that is, when it executes its program to control an ex

ternal system, a series of operations are performed inside the PC. These in

ternal operations can be broadly classified into the following four categories:

Common (or overseeing) processes, such as watchdog timer operation

and testing the program memory.

Data input and output.

Instruction execution.

Peripheral device servicing.

The total time required for a PC to perform all these internal operations is

called the cycle time. The flowchart and diagram on page 7 illustrate these

internal operations for a typical PC.

Timing is one of the most important factors in designing a Control System.

For accurate operations, it is necessary to have answers to such questions

as these:

• How long does it take for the PC to execute all the instructions in its mem

ory