The output lines on these boards can either source or sink current to an actuator (or a sensor) depending on the type of actuator. Therefore, different signal connection schemes are required for proper operation.
: A sourcing device provides the power or a positive potential. Sourcing devices "push" the current through the load to ground. Terms used to describe sourcing devices include PNP, Open Emitter, Normally Low, and IEC Positive Logic.
The NI PCI-6512, PCI-6514, PCI-6516, PCI-6518, PXI-6512, and PXI-6514 (even-numbered NI 651
devices with outputs) are few of the NI DIO devices that have sourcing digital outputs.
: A sinking device provides a path for the current to ground and is not responsible for powering the device. Terms used to describe sinking devices include NPN, Open Collector, Normally High, and IEC Negative Logic.
The NI PCI-6513, PCI-6515, PCI-6517, PCI-6519, PXI-6513, and PXI-6515 (odd-numbered NI 651
devices with outputs) are a few of the NI DIO devices that have sinking digital outputs.
For both sourcing and sinking NI 651
devices, the output port requires an external power supply to operate. The voltage from this power supply is regulated and passed to the 30 V bank isolated output driver called the Darlington Driver.
For more information on these concepts, refer to
Digital I/O Sinking and Sourcing