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DC Voltages
© National Instruments Corporation
Input Ranges
The DAQCard-4050 has five input ranges available for measuring DC
voltages. These ranges are ±20 mV, ±200 mV, ±2.0 V, ±25 V, and
±250 V. The DAQCard-4050 can measure DC voltages to its specified
accuracy as long as the voltage is within the selected input range. The
DAQCard-4050 can measure voltages outside of the input range (the
overrange) with reduced accuracy. Table 3-1 shows the accuracy,
typical overrange, and input impedance of each of the input ranges.
Table 3-1. DC Input Range Accuracy
Input
Percent of
Range
Reading
Error
±20 mV
0.005%
±200 mV
0.005%
±2.0 V
0.004%
±25 V
0.006%
±250 V
0.006%
Accuracy Considerations
If you are making sensitive measurements (measurements that need a
high degree of accuracy), you should consider problems associated with
input impedance, AC noise effects, and thermal electromotive forces
(thermal EMFs).
Input Impedance
The input impedance of the DAQCard-4050 can cause additional span
errors by creating an attenuator with the impedance of the circuit under
test. Although the high (>1 GΩ) impedance in the lower three input
ranges is not likely to cause any significant errors, the lower impedance
of the ±25 V and ±250 V ranges can attenuate (make smaller) the signal
being measured.
Percent of
Range
Error
0.1%
0.025%
0.01%
0.035%
0.007%
3-3
DAQMeter DAQCard-4050 User Manual
Chapter 3
DMM Operation
Overrange
Input
Impedance
±22 mV
> 1 GΩ
±220 mV
> 1 GΩ
±2.2 V
> 1 GΩ
±27 V
1 MΩ
±250 V
1 MΩ
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