Installation,
Wiring,
and
Specifications
2--18
Installation, Wiring, and Specifications
DL105 PLC User Manual, 3rd Edition
Before going further in our study of wiring strategies, we must have a solid
understanding of “
sinking
” and “
sourcing
” concepts. Use of these terms occurs
frequently in input or output circuit discussions. It is the goal of this section to make
these concepts easy to understand, further ensuring your success in installation.
First we give the following short definitions, followed by practical applications.
Sinking =
Path to supply
ground (--)
Sourcing =
Path to supply
source (+)
First you will notice that these are only associated with DC circuits and not AC,
because of the reference to (+) and (--) polarities. Therefore,
sinking and sourcing
terminology only applies to DC input and output circuits.
Input and output points that
are either sinking or sourcing can conduct current in only one direction. This means it
is possible to connect the external supply and field device to the I/O point with current
trying to flow in the wrong direction, and the circuit will not operate. However, we can
successfully connect the supply and field device every time by understanding
“sourcing” and “sinking”.
For example, the figure to the right depicts
a “sinking” input. To properly connect the
external supply, we just have to connect it
so the the input
provides a path to ground
(--)
. So, we start at the PLC input terminal,
follow through the input sensing circuit,
exit at the common terminal, and connect
the supply (--) to the common terminal. By
adding the switch, between the supply (+)
and the input, we have completed the
circuit. Current flows in the direction of the
arrow when the switch is closed.
+
--
Input
Sensing
PLC
Input
Common
(sinking)
By applying the circuit principle above to the four possible combinations of
input/output sinking/sourcing types, we have the four circuits as shown below.
DL105 Micro PLCs provide all except the sourcing output I/O circuit types.
+
--
Input
Sensing
Load
Sinking Input
Sinking Output
Sourcing Input
Sourcing Output
PLC
Input
Common
+
--
Output
Switch
PLC
Output
Common
+
--
Input
Sensing
Load
PLC
Input
Common
+
--
Output
Switch
PLC
Output
Common
Sinking / Sourcing
Concepts
Содержание DL105
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