OMRON C60H-C6DR-DE-V1 Programmable Controllers

OMRON C60H-C6DR-DE-V1  Programmable Controllers

A PC(Programmable Controller) is basically a CPU (Central Processing Unit)

containing a program and connected to input and output (I/O) devices. The

program controls the PC so that when an input signal from an input device

turns ON, the appropriate response is made. The response normally involves

turning ON an output signal to an output device. The input devices could be

photoelectric sensors, pushbuttons on control panels, limit switches, or any

other device that can produce a signal that can be input into the PC. The out

put devices could be solenoids, switches activating indicator lamps, relays

turning on motors, or any other devices that can be activated by signals out

put from the PC.

For example, a sensor detecting a passing product turns ON an input to the

PC. The PC responds by turning ON an output that activates a pusher that

pushes the product onto another conveyor for further processing. Another

sensor, positioned higher than the first, turns ON a different input to indicate

that the product is too tall. The PC responds by turning on another pusher

positioned before the pusher mentioned above to push the too-tall product

into a rejection box.

Although this example involves only two inputs and two outputs, it is typical of

the type of control operation that PCs can achieve. Actually even this exam

ple is much more complex than it may at first appear because of the timing

that would be required, i.e., “How does the PC know when to activate each

pusher?” Much more complicated operations, however, are also possible.

The problem is how to get the desired control signals from available inputs at

appropriate times.

To achieve proper control, the Mini H-type PCs, like the other C-series PCs,

use a form of PC logic called ladder-diagram programming. This manual is

written to explain ladder-diagram programming and to prepare the reader to

program and operate the Mini H-type PCs.

1-2 TheOrigins of PC Logic

PCs historically originate in relay-based control systems. Although the inte

grated circuits and internal logic of the PC have taken the place of the dis

crete relays, timers, counters, and other such devices, actual PC operation

proceeds as if those discrete devices were still in place. PC control, however,

also provides computer capabilities and accuracy to achieve a great deal

more flexibility and reliability than is possible with relays.

The symbols and other control concepts used to describe PC operation also

come from relay-based control and form the basis of the ladder-diagram pro

gramming method. Most of the terms used to describe these symbols and

concepts, however, have come in from computer terminology.

1-3 PCTerminology

Although also provided in the Glossary at the back of this manual, the follow

ing terms are crucial to understanding PC operation and are thus explained

here.

Inputs and Outputs

A device connected to the PC that sends a signal to the PC is called an input

device; the signal it sends is called an input signal. A signal enters the PC

through terminals or through pins on a connector on a Unit. The place where

a signal enters the PC is called an input point. This input point is allocated a

location in memory that reflects its status, i.e., either ON or OFF. This mem

ory location is called an input bit. The CPU, in its normal processing cycle