DL06 Micro PLC User Manual, 3rd Edition, Rev. E
Chapter 2: Installation, Wiring, and Specifications
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Sinking / Sourcing Concepts
Before going further in our presentation of wiring strategies, we need to introduce the concepts
of
sinking
and
sourcing
. These terms apply to typical input or output circuits. It is the goal
of this section to make these concepts easy to understand. First, we give the following short
definitions, followed by practical applications.
Sinking = Path to supply ground (–)
Sourcing = Path to supply source (+)
Notice the reference to (+) and (–) polarities. Sinking and sourcing terminology applies only 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
sinkin
g input. To properly connect the external
supply, we just have to connect it so the input provides a path to ground (–). So, we start at
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. The DC-powered DL06
Micro PLCs have selectable
sinking
or
sourcing
inputs and either
sinking
or
sourcing
outputs.
Any pair of input/output circuits shown below is possible with one of the DL06 models.
+
–
Input
Sensing
PLC
Common
Input
(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
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.
