National Instruments NI 6120 用户手册
Chapter 3
Hardware Overview
3-8
ni.com
In low-hysteresis analog triggering mode, the trigger is generated when
the signal value is less than lowValue, with the hysteresis specified by
highValue, as Figure 3-8 shows.
the signal value is less than lowValue, with the hysteresis specified by
highValue, as Figure 3-8 shows.
Figure 3-8. Low-Hysteresis Analog Triggering Mode
The analog trigger circuit generates an internal digital trigger based on the
AI signal and the user-defined trigger levels. This digital trigger can be
used by any of the timing sections of the DAQ-STC, including the AI, AO,
and general-purpose counter/timer sections. For example, the AI section
can be configured to acquire n scans after the AI signal crosses a specific
threshold. As another example, the AO section can be configured to update
its outputs whenever the AI signal crosses a specific threshold.
AI signal and the user-defined trigger levels. This digital trigger can be
used by any of the timing sections of the DAQ-STC, including the AI, AO,
and general-purpose counter/timer sections. For example, the AI section
can be configured to acquire n scans after the AI signal crosses a specific
threshold. As another example, the AO section can be configured to update
its outputs whenever the AI signal crosses a specific threshold.
Antialiasing Filters
Each AI channel on the NI 6115/6120 is equipped with a programmable
antialaising Bessel filter. On the NI 6115, you can program the filters to
provide a third-order 50 kHz lowpass filter, a third-order 500 kHz lowpass
filter, or a pass-through mode with no filtering. On the NI 6120, you can
program the filters to provide a five-pole 100 kHz low-pass filter or
pass-through. These Bessel filters are highly effective at reducing signal
aliasing and are designed for use with software filters.
antialaising Bessel filter. On the NI 6115, you can program the filters to
provide a third-order 50 kHz lowpass filter, a third-order 500 kHz lowpass
filter, or a pass-through mode with no filtering. On the NI 6120, you can
program the filters to provide a five-pole 100 kHz low-pass filter or
pass-through. These Bessel filters are highly effective at reducing signal
aliasing and are designed for use with software filters.
Existing software algorithms alone provide good roll-off at the cut-off
frequency as shown in Figure 3-9. However, aliasing can cause
high-frequency harmonics to make it through passbands in the filter. By
combining hardware and software filtering, it is possible to obtain both
steep roll-off and clean filtering of high-frequency aliases.
frequency as shown in Figure 3-9. However, aliasing can cause
high-frequency harmonics to make it through passbands in the filter. By
combining hardware and software filtering, it is possible to obtain both
steep roll-off and clean filtering of high-frequency aliases.
highValue
Trigger
lowValue