Accuracy - Measurement Computing USB-1608FS-Plus-OEM User Manual

USB-1608FS-Plus-OEM User's Guide

Accuracy

The overall accuracy of any instrument is limited by the error components within the system. Resolution is
often used incorrectly to quantify the performance of a measurement product. While "16-bits" or "1 part in
65,536" does indicate what can be resolved, it provides little insight into the quality, or accuracy, of an absolute
measurement.
Accuracy specifications describe the actual measurement achievable with a USB-1608FS-Plus-OEM.
specifications are listed on page 17.
There are three types of errors which affect the accuracy of a measurement system:

offset

gain

nonlinearity
The primary error sources in a USB-1608FS-Plus-OEM are offset and gain. Nonlinearity is small, and is not
significant as an error source with respect to offset and gain.
Figure 6 shows an ideal, error-free transfer function. The typical calibrated accuracy of a USB-1608FS-Plus-
OEM is range-dependent. We use a ±10 V range as an example of what you can expect when performing a
measurement in this range.
The offset error is measured at mid-scale. Ideally, a zero volt input should produce an output code of 32,768.
Any deviation from this is an offset error. Figure 7 shows the transfer function with an offset error. The typical
offset error specification for a USB-1608FS-Plus-OEM on the ±10 V range is ±1.66 mV. Offset error affects all
codes equally by shifting the entire transfer function up or down along the input voltage axis.
The accuracy plots in Figure 7 are drawn for clarity and are not drawn to scale.
Figure 6. Ideal ADC transfer function
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Functional Details
Accuracy