Measurement Computing USB-1208LS - Page 22

USB-1208LS User's Guide Functional Details
-FS
+FS
Input Voltage
0
4095
Output Code
2048
Figure 3-10. Ideal ADC transfer function
The USB-1208LS 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. Fi shows the USB-1208LS 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.
gure 3-11
Figure 3-11. ADC transfer function with offset error
The accuracy plots in Figure 3-11 are drawn for clarity and are not drawn to scale.
-FS
+FS
Input Voltag
e
0
4095
2
Offset=9.77mV
Ideal
Actual
Output Code
9.77mV
2048
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. shows the USB-1208LS transfer function with gain error. Gain error is
easily converted to voltage by multiplying the full-scale (FS) input by the error.
Figure 3-12
3-10