USB-2416-4AO User's Guide
Functional Details
17
The
non-isolated
ground is common to the chassis ground of the computer, while the
isolated
ground is not.
All analog measurements are made relative to the isolated ground. See Figure 12 for details.
Figure 12. USB-2416-4AO input isolation diagram
When making measurements in industrial environments, DAQ devices can encounter hazardous voltages,
transients, large common mode voltages and fluctuating ground potentials. Any one of these issues can
seriously degrade the measurement accuracy of the device and possibly damage the measurement instrument.
To overcome these issues, some DAQ devices provide physical and electrical isolation. Some of the benefits of
isolation include:
Safety: A DAQ device employing physical and electrical isolation helps to keep high voltages and
transients from damaging the system-side host PC.
Ground loops: Improper grounding of the signal source that the DAQ device is measuring is one of the
most common sources of noise and measurement inaccuracies. Isolation improves the measurement
accuracy by physically preventing ground loops. Ground loops—a common source of noise and error—are
the results of a measurement system having multiple grounds at different potentials.
Common mode rejection: With isolation, a DAQ device can measure small signals in the presence of large
common mode voltages. Isolation increases the measurement system's ability to reject common mode
voltages. The common mode voltage is the signal that is common to both the positive and negative inputs
of the measurement device, but is not part of the signal to measure.
Analog output terminals (VDAC0 through VDAC3)
The USB-2416-4AO has four 16-bit analog output channels with a ±10 V output range.
Analog outputs can be updated at a maximum rate of 1 kS/s.
Digital I/O
The USB-2416-4AO provides up to eight digital I/O lines with read/write rates of 500 port reads or single bit
reads per second.
Digital input voltage ranges of 0 V to 15 V are permitted, with thresholds of 0.6 V (low) and 2.6 V (high). Each
DIO channel is an
open-drain
, which, when used as an output, is capable of sinking up to 150 mA for direct
drive applications. The maximum sink current is 150 mA per eight-channel bank, or if all eight channels are
used, 18 mA (maximum) per channel.
Figure 13 is an example of a typical DIO connection. The figure represents connections for one channel. The
other seven channels are connected in the same manner.
