Rockwell Automation 1747-L5xx SLC 500 Modular Hardware Style User Manual - Manual (Page 112)

Publication 1747-UM011G-EN-P - June 2008
112 Wiring Your I/O Modules
Contact Output Circuits — ac or dc
Relays can be used for either ac or dc output circuits and
accommodate either sinking or sourcing field devices. These
capabilities are a result of the output switch being a mechanical
contact closure, not sensitive to current flow direction and capable of
accommodating a broad range of voltages.
This high degree of application flexibility makes contact output
modules very popular and useful in control environments with a
broad mix of electrical I/O circuit requirements.
Solid-State dc I/O Circuits
The design of dc field devices typically requires that they be used in a
specific sinking or sourcing circuit depending on the internal circuitry
of the device. DC input and output field circuits are commonly used
with field devices that have some form of internal solid state circuitry
that need a dc signal voltage to function.
Sourcing Device with Sinking Input Module Circuit
The field device is on the positive side of the power supply between
the supply and the input terminal. When the field device is activated,
it sources current to the input circuit.
+
_
I Field Device
dc Power
Supply
dc Com
Input
dc
Input
Circuit