Measurement-computing USB-1608FS-Plus Manuel d'utilisateur télécharger pdf (Page 14)

USB-1608FS-Plus User's Guide Functional Details

There are three types of errors which affect the accuracy of a measurement system:

 offset

 gain

 nonlinearity

The primary error sources in a 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 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 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 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.

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Measurement-computing USB-1608FS-Plus Manuel d'utilisateur Page 14