AutomationDirect DL205 User Manual

DL205 User Manual, 4th Edition, Rev. D
2-17
Chapter 2: Installation, Wiring and Specifications
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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 at the end of this chapter 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

AutomationDirect DL205 Specifications

General

Brand	AutomationDirect
Model	DL205
Category	Controller
Language	English