Measurement Computing USB-1208FS - Manual (Page 17)

USB-1208FS User's Guide Functional Details
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Figure 11 shows an ideal, error-free, USB-1208FS transfer function. The typical calibrated accuracy of the
USB-1208FS is range-dependent, as explained in the
Specifications chapter on page 20. We use a ±10 V range
here as an example of what you can expect when performing a measurement in this range.
Figure 11. Ideal ADC transfer function
The USB-1208FS offset error is measured at mid-scale. Ideally, a zero volt input should produce an output code
of 2048. Any deviation from this is an offset error. Figure 12 shows the USB-1208FS transfer function with an
offset error. The typical offset error specification on the ±10 V range is ±9.77 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 12 are drawn for clarity and are not drawn to scale.
Figure 12. 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 13 shows the USB-1208FS transfer function with gain error. Gain error is easily
converted to voltage by multiplying the full-scale (
FS ) input by the error.