AutomationDirect DL105, User Manual

Page: 51 / 350

Installation,
Wiring,
and
Specifications
2--20
Installation, Wiring, and Specifications
DL105 PLC User Manual, 3rd Edition
In the previous section on Sourcing and Sinking concepts, we explained that DC I/O
circuits sometimes will 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, one must be wired as sourcing and the other as sinking .
The DL105’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 +24 auxiliary supply
or another supply (+12 VDC or +24VDC), as long as the input specifications are met.
Field Device
+ --
PLC DC Input
Output
Ground
Input
Common
Supply
(sinking)
(sourcing)
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.
Field Device
PLC DC Input
Output (sourcing)
Ground
Input
Common
+V
(sinking)
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 DL105’s DC outputs are sinking-only. This means that each DC output provides
a path to ground when it is energized. Also, remember that all eight outputs have the
same electrical common, even though there are three common terminal screws.
Finally, recall that the DC output circuit requires power (10 -- 30 VDC) from an
external power source.
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.
Field Device
Output
Ground
Input
Common
+V
PLC DC Output
+DC pwr
+
--
(sourcing)
(sinking)
Power
10--30 VDC
Connecting DC I/O
to “Solid State”
Field Devices
Solid State
Input Sensors
Solid State
Output Loads