DL06 Micro PLC User Manual, 3rd Edition, Rev. E
Chapter 2: Installation, Wiring, and Specifications
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Connecting DC I/O to Solid State Field Devices
In the previous section on sinking and sourcing concepts, we discussed DC I/O circuits that
only allow current to flow one way. This is also true for many of the field devices which have
solid-state (transistor) interfaces. In other words, field devices can also be sourcing or sinking.
When connecting two devices in a series DC circuit (as is the case when wiring a field device to a
PLC DC input or output), one must be wired as sourcing and the other as sinking.
Solid State Input Sensors
The DL06’s DC inputs are flexible in that they detect current flow in either direction, so they
can be wired as either sourcing or sinking. In the following circuit, a field device has an open-
collector NPN transistor output. It sinks current from the PLC input point, which sources
current. The power supply can be the included auxiliary 24VDC power supply or another
supply (+12VDC or +24VDC), as long as the input specifications are met.
In the next circuit, a field device has an open-emitter PNP transistor output. It sources current
to the PLC input point, which sinks the current back to ground. Since the field device is
sourcing current, no additional power supply is required between the device and the PLC DC
Input.
Solid State Output Loads
Sometimes an application requires connecting a PLC output point to a solid state input on
a device. This type of connection is usually made to carry a low-level signal, not to send DC
power to an actuator.
The DL06 PLC family offers DC outputs that are sinking only or DC outputs that are
sourcing. All sixteen outputs have the same electrical common, even though there are four
common terminal screws. In the following circuit, the PLC output point sinks current to the
output common when energized. It is connected to a sourcing input of a field device input.
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