Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 21)

An Introduction to
Programmable Controllers
Chapter 2
2Ć7
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 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 isolates the machine circuitry from the programmable controller’s
circuitry. Isolation helps 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
The third section is the output, which serves functions similar to those of the
input image table:
termination
indication
conditioning
isolation
Termination
The output provides terminals for the field wiring going to the output devices on
the machine.
Indication
The output of most modules provides a visual indication of the selected state of
each output device with indicators.
The output status indicator is 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.
In addition, the output section of modules with fuses has blown fuse indicators.
When one of the fuses in the group opens, the blown fuse indicator lights.
Conditioning
The output conditions the programmable controller’s signals for the machine.
That is, it converts the low-level dc voltages of the programmable controller to
the type of electrical power used by the output devices at the machine.