Chapter 3
DMM Operation
DAQMeter DAQCard-4050 User Manual
3-6
©
National Instruments Corporation
The impedance in each of these ranges is 1 M
Ω
. The DC component in
any of these ranges can be as high as 250 VDC.
Accuracy Considerations
The AC voltage measurement accuracy is dependent on many factors,
including the signal amplitude, frequency, and waveform shape
(or crest factor). Each of these factors, and their effects on your
measurements, are discussed below. In addition to these factors,
consider the effects of the source impedance of your circuit. These
effects are described in the Input Impedance section earlier in this
chapter.
Frequency Response
The accuracy of the DAQCard-4050’s AC voltage measurements is a
function of the input signal’s frequency. Table 3-3 shows the additional
measurement errors associated with different frequency ranges. These
errors are for full-scale, sine wave inputs.
Table 3-2.
AC Input Range Accuracy
Input
Range
Percent of
Reading Error
Percent of
Range Error
Overrange
20 mV
rms
0.3%
0.1%
22 mV
rms
200 mV
rms
0.3%
0.1%
220 mV
rms
2.0 V
rms
0.4%
0.2%
2.2 V
rms
25 V
rms
0.4%
0.2%
27 V
rms
250 V
rms
0.3%
0.1%
250 V
rms