Do-more H2 Series PLC User Manual, 1st Edition, Rev. F - H2-DM-M
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Chapter 8: Installation and Wiring
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Sinking / Sourcing Concepts
Before going further in the study of wiring strategies, you 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 the following short definitions are provided,
followed by practical applications.
Sinking = provides a path to supply ground (–)
Sourcing = provides a path to supply source (+)
First you will notice 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 sinking only or sourcing
only 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, you 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, you
will have to connect it so the input provides a path to
ground (–). 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, the circuit has been completed .
Current flows in the direction of the arrow when the
switch is closed.
Apply the circuit principle above to the four possible
combinations of input/output sinking/sourcing types as shown below. The I/O module
specifications found in the “Specifications” chapters list the input or output type.
+
–
Input
Sensing
PLC
Input
Common
(sinking)
+
–
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
Содержание Do-more H2 PLC Series
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