ALLEN BRADLEY 1747-L551 PLC Processor

7–2
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.
+
DC POWER
SUPPLY
_
FIELD DEVICE
I
Input
DC
INPUT
CIRCUIT
DC Com
Publication 1747-6.2