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Chapter 4
Theory of Operation
©
National Instruments Corporation
4-25
NI PXI-4220 User Manual
For example, if you have a 0–500 psi pressure sensor with 3.0 mV/V
sensitivity, an excitation voltage of 10 V, and a maximum pressure of
200 psi, the maximum signal is:
For example, because the NI PXI-4220 DAQ circuitry has a maximum
analog input range of ±10 V and you have set the maximum input to the
NI PXI-4220 to be +12 mV, set the gain to the setting closest to
but
less
than 833. A larger gain setting saturates the NI PXI-4220 DAQ
circuitry for a 12 mV signal. In this example, the closest gain that is less
than 833 for the NI PXI-4220 is 750.
Refer to the
Configurable Settings in MAX
section of Chapter 3,
Configuring and Testing
, for more information about programmatically
setting gain using range settings in MAX. For more information about
programmatically setting gain using range settings in NI-DAQmx, refer to
the
Developing Your Application in NI-DAQmx
section of Chapter 5,
Developing Your Application
.
Filter
The NI PXI-4220 provides two filtering stages with an overall response of
a four-pole Butterworth filter. You can control the cutoff frequency of the
filter through software. You can choose 10 Hz, 100 Hz, 1 kHz, 10 kHz,
or filter bypass to disable the filter. For additional flexibility in cutoff
frequency settings and for greater upper-band suppression in the stop-band,
NI recommends combining the hardware filtering provided by the
NI PXI-4220 with digital filtering. NI recommends using the Advanced
Analysis functions of LabVIEW for digital filtering, for example the Filter
Express VI available at
Functions»Analysis
. The Advanced Analysis
functions are only available in LabVIEW Full or Professional versions.
Refer to the
Configurable Settings in MAX
section of Chapter 3,
Configuring and Testing
, for more information about programmatically
setting the cutoff frequency of the filter in MAX. For more information
about programmatically setting the cutoff frequency of the filter in
NI-DAQmx, refer to the
Developing Your Application in NI-DAQmx
section of Chapter 5,
Developing Your Application
.
12 mV
3.0 mV/V
(
)
10 V
(
)
200 psi
(
)
×
×
500 psi
(
)
--------------------------------------------------------------------------------
=
833
10 V
12 mV
----------------
=
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