Measurement Computing USB-1408FS User Manual page 22

USB-1408FS User's Guide
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
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 (
Input Voltage
+10V
0
-10V
Figure 11. Ideal ADC transfer function
are drawn for clarity and are not drawn to scale.
Figure 12
Input Voltage
+10V
Offset=2.44mV
8192
0
Actual
-10V
Figure 12. ADC transfer function with offset error
Output Code
8192 16383
Ideal
Output Code
2.44mV
16383
) input by the error.
FS
22
Functional Details