Advantech iDAQ-731 User Manual page 21

For a source type digital output, the external source is connected to the digital output
common (DOCOM) terminal. The current which flows through the load is sourced
from the DO terminal. This is shown in Figure 2.5. Connect the negative terminal of
the external source to the DOGND terminal for a correct potential reference.
Figure 2.5 Source (PNP) type digital output signal connection.
Both the voltage of the external source and the load current must be within the range
as specified in the device specifications for proper operation and to prevent the
device from damaging. The expected load current in amps can be calculated by the
following equation.
where...
V is the voltage of the external source in volts,
EXT
R is the load resistance in ohms, and
LOAD
R is the internal resistance of the switch in ohms, which can be found in
INT
the device specifications.
The device is also equipped with flyback diodes and resettable fuses (polyswitches)
for each channel. The flyback diode provides a continuous current path for inductive
load to dissipate energy when the digital output channel becomes OFF. This prevents
the inductive load from generating a large back EMF which may damage the device.
The resettable fuse disconnects the circuit when over-current condition occurs, which
prevents the internal MOSFET switch from begin damaged. It automatically resets
(reconnects circuit) after over-current condition is removed.
11 iDAQ-731_751_763D User Manual