Owner's manual

OM-USB-1608FS-Plus User's Guide Functional Details
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There are three types of errors which affect the accuracy of a measurement system:
 offset
 gain
 nonlinearity
The primary error sources in a OM-USB-1608FS-Plus are offset and gain. Nonlinearity is small, and is not
significant as an error source with respect to offset and gain.
Figure 7 shows an ideal, error-free transfer function. The typical calibrated accuracy of a OM-USB-1608FS-
Plus is range-dependent. We use a ±10 V range as an example of what you can expect when performing a
measurement in this range.
Figure 7. Ideal ADC transfer function
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 8 shows the transfer function with an offset error. The typical
offset error specification for a OM-USB-1608FS-Plus 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 8 are drawn for clarity and are not drawn to scale.
Figure 8. ADC transfer function with offset error
Gain error is a change in the slope of the transfer function from the ideal, and is typically expressed as a
percentage of full-scale. Figure 9 shows the OM-USB-1608FS-Plustransfer function with gain error. Gain error
is easily converted to voltage by multiplying the full-scale input (±10 V) by the error.