10.0 SGND and GND [T-Series Datasheet]

SGND (T4 and T7)

SGND is located near the upper-left of the device. This terminal has a self-resetting thermal fuse in series with GND. This is often a good terminal to use when connecting the ground from another separately powered system that could unknowingly already share a common ground with the T4 or T7.

See the AIN, DAC, and Digital I/O application notes for more information about grounding.

GND

The GND connections available at the screw-terminals and DB connectors provide a common ground for all LabJack functions. All GND terminals are the same and connect to the same ground plane.

GND is also connected to the ground pin on the USB connector, so if there is a connection to a USB port on a hub/host (as opposed to just a power supply connection), then GND is the same as the ground line on the USB connection, which is often the same as ground on the PC chassis, which is often the same as AC mains ground.

For more information about grounding, see the 14.0 AIN, 15.0 DAC, and 13.0 Digital I/O sections.

The max total current that can be sunk into GND is:

T4, T7: Max total current = 500mA - DeviceSupplyCurrent

T8: Max total current = 1100mA - DeviceSupplyCurrent

For example, if the T7 needs 250mA to run, the current sunk into GND terminals should be limited to 250mA. Note that sinking substantial current into GND can cause slight voltage differences between different ground terminals, which can cause noticeable errors with single-ended analog input readings. For information about device supply current, see 9.0 VS, Power Supply.