Measurement Computing USB-1408FS User Manual
Page 17
USB-1408FS User's Guide
Functional Details
17
Figure 11 shows an example of an ideal, error-free, USB-1408FS transfer function. The typical calibrated
accuracy of the USB-1408FS is range-dependent, as explained in the "
" 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 offset error is measured at mid-scale. Ideally, a zero volt input should produce an output code of 8192. Any
deviation from this is an offset error.
Figure 12 shows an example of a USB-1408FS transfer function with a ±2.44 mV offset error. 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-1408FS transfer function with gain error. Gain error is easily
converted to voltage by multiplying the full-scale (
FS
) input by the error.
The accuracy plots in Figure 13 are drawn for clarity and are not drawn to scale.