Rockwell Automation 1747-ACNR15 ControlNet Adapter Module User Manual - Manual (Page 118)

Publication 1747-UM003A-EN-P
B-26 Understanding Your SLC 500/1746 Control System
Definition of Sinking and Sourcing
Sinking and sourcing are terms used to describe a current signal flow
relationship between field input and output devices in a control system and
their power supply.
•
Field devices connected to the positive side (+V) of the field power supply
are sourcing field devices.
•
Field devices connected to the negative side (dc Common) of the field
power supply are called sinking field devices.
To maintain electrical compatibility between field devices and the
programmable controller system, this definition is extended to the input/
output circuits on the discrete I/O modules.
•
Sourcing I/O circuits supply (source) current to sinking field devices.
•
Sinking I/O circuits receive (sink) current from sourcing field devices.
Europe: The dc sinking input and sourcing output module circuits are the
commonly used options.
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.
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.
The 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.