National Instruments DAQ X NI 634 Series, Руководство пользователя

Страница: 80 / 278

© National Instruments
|
4-37
X Series User Manual
Analog Input Terminal Configuration
Simultaneous MIO X Series devices support only differential (DIFF) input mode. The channels
on Simultaneous MIO X Series devices are true differential inputs, meaning both positive and
negative inputs can carry signals of interest. For more information about DIFF input, refer to the
Connecting Analog Input Signals section, which contains diagrams showing the signal paths for
DIFF input mode.
Caution Exceeding the differential and common-mode input ranges distorts the
input signals. Exceeding the maximum input voltage rating can damage the device
and the computer. NI is
not liable for any damage resulting from such signal
connections. The maximum input voltage ratings can be found in the specifications
for each Simultaneous MIO X Series device.
Analog Input Range
Input range refers to the set of input voltages that an analog input channel can digitize with the
specified accuracy. The NI-PGIA amplifies or attenuates the AI signal depending on the input
range. You can individually program the input range of each AI channel on your Simultaneous
MIO X Series device.
The input range affects the resolution of the Simultaneous MIO X Series device for an AI
channel. Resolution refers to the voltage of one ADC code. For example, a 16-bit ADC converts
analog inputs into one of 65,536 (= 2
16
) codes—that is, one of 65,536 possible digital values.
These values are spread fairly evenly across the input range. So, for an input range of -10 V to
10 V, the voltage of each code of a 16-bit ADC is:
Simultaneous MIO X Series devices use a calibration method that requires some codes (typically
about 5% of the codes) to lie outside of the specified range. This calibration method improves
absolute accuracy, but it increases the nominal resolution of input ranges by about 5% over what
the formula shown above would indicate.
Choose an input range that matches the expected input range of your signal. A large input range
can accommodate a large signal variation, but reduces the voltage resolution. Choosing a smaller
input range improves the voltage resolution, but may result in the input signal going out of range.
For more information about setting ranges, refer to the NI-DAQmx Help or the LabVIEW Help .
10V 10V
–
 
–
2
16
---------------------------------
305

V
=