Rockwell-automation 1772-LV Mini-PLC - 2/15 Programmable Controller (S Instrukcja Użytkownika Pobierz pdf (Strona 11)

An Introduction to Programmable

Controllers

Chapter 2

24

Indication

The input section of most modules also provides a visual indication of the state

of each input terminal with indicators. The indicator is on when there is a

voltage applied to its terminal. It is off when there is no voltage applied to its

terminal. Since the indicator reveals the status of its terminal, it’s usually called

an input status indicator.

You should also notice another important characteristic of input indicators.

They are only associated with terminals used for wiring sensing devices to the

input section. The terminal that’s used to provide a ground for the sensing

circuits has no indicator.

Conditioning

Another function of the input section is signal conditioning. The electrical

power used at the machine is usually not compatible with the signal power used

within the programmable controller. Therefore, the input section receives the

electrical signal from the machine and converts it to a voltage compatible with

the programmable controller’s circuitry.

Isolation

The input section isolates the machine circuitry from the programmable

controller’s circuitry. Isolation helps to protect the programmable controller’s

circuitry from unwanted and dangerous voltage levels that may occur

occasionally at the machine or in the plant’s wiring system.

Output

Section

The output section has functions similar to those of the input section:

Termination

Indication

Conditioning

Isolation

Termination

The output section provides terminals for the field wiring going to the output

devices on the machine.

Indication

The output section of most modules provides a visual indication of the state of

each output device with indicators.

The output status indicator will be on when the output device is energized. A

common term applied to either input status indicators or output status indicators

is I/O status indicators. I/O stands for either input or output.

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Rockwell-automation 1772-LV Mini-PLC - 2/15 Programmable Controller (S Instrukcja Użytkownika Strona 11