Considerations For Selecting Analog Input Ranges; Table 2-8. Actual Range And Measurement Precision Versus Input Range Selection And Gain - National Instruments AT-MIO-16D User Manual

Configuration and Installation

Considerations for Selecting Analog Input Ranges

Analog input polarity/range selection depends on the expected input range of the incoming signal.
A large input range can accommodate a large signal variation but sacrifices voltage resolution.
Choosing a smaller input range increases voltage resolution but may result in the input signal
going out of range. For best results, the input range should be matched as closely as possible to
the expected range of the input signal. For example, if the input signal is guaranteed to never go
negative (below 0 V), a unipolar input is best. However, if the signal does go negative, inaccurate
readings will occur.
Software-programmable gain on the AT-MIO-16D increases overall flexibility by matching input
signal ranges to those accommodated by the AT-MIO-16D analog-to-digital converter (ADC).
The AT-MIO-16DH board has gains of 1, 2, 4, and 8 and is suited for high-level signals near the
range of the ADC. The AT-MIO-16DL board is designed to measure low-level signals and has
gains of 1, 10, 100, and 500. With the proper gain setting, the full resolution of the ADC can be
used to measure the input signal. Table 2-8 shows the overall input range and precision according
to the input range configuration and gain used.

Table 2-8. Actual Range and Measurement Precision Versus Input Range Selection and Gain

Range Configuration
0 to +10 V
-5 to +5 V
-10 to +10 V
* The value of 1 LSB of the 12-bit ADC, that is, the voltage increment corresponding to a
change of 1 count in the ADC 12-bit count.
AT-MIO-16D User Manual
Gain Actual Input Range
1 0 to +10 V
2 0 to +5 V
4 0 to +2.5 V
8 0 to +1.25 V
10 0 to +1 V
100 0 to +0.1 V
500 0 mV to +20 mV
1 -5 to +5 V
2 -2.5 to +2.5 V
4 -1.25 to +1.25 V
8 -0.625 to +0.625 V
10 -0.5 to +0.5 V
100 -50 mV to +50 mV
500 -10 mV to +10 mV
1 -10 to +10 V
2 -5 to +5 V
4 -2.5 to +2.5 V
8 -1.25 to +1.25 V
10 -1 to +1 V
100 -0.1 to +0.1 V
500 -20 mV to +20 mV
2-14
Precision*
2.44 mV
1.22 mV
610 µV
305 µV
244 µV
24.4 µV
4.88 µV
2.44 mV
1.22 mV
610 µV
305 µV
244 µV
24.4 µV
4.88 µV
4.88 mV
2.44 mV
1.22 mV
610 µV
488 µV
48.8 µV
9.76 µV
© National Instruments Corporation
Chapter 2