Omega OM-USB-1208FS User Manual
OM-USB-1208FS User's Guide
Functional Details
18
Accuracy
The overall accuracy of any instrument is limited by the error components within the system. Quite often,
resolution is incorrectly used to quantify the performance of a measurement product. While "12-bits" or "1 part
in 4096" does indicate what can be resolved, it provides little insight into the quality of an absolute
measurement. Accuracy specifications describe the actual results that can be realized with a measurement
device.
resolution is incorrectly used to quantify the performance of a measurement product. While "12-bits" or "1 part
in 4096" does indicate what can be resolved, it provides little insight into the quality of an absolute
measurement. Accuracy specifications describe the actual results that can be realized with a measurement
device.
There are three types of errors which affect the accuracy of a measurement system:
offset
gain
nonlinearity.
gain
nonlinearity.
The primary error sources in the OM-USB-1208FS are offset and gain. Nonlinearity is small in the OM-USB-
1208FS, and is not significant as an error source with respect to offset and gain.
1208FS, and is not significant as an error source with respect to offset and gain.
Figure 9 shows an ideal, error-free, OM-USB-1208FS transfer function. The typical calibrated accuracy of the
OM-USB-1208FS is range-dependent, as explained in the "
OM-USB-1208FS is range-dependent, as explained in the "
" chapter on page 22. We use a ±10 V
range here as an example of what you can expect when performing a measurement in this range.
Figure 9. Ideal ADC transfer function
The OM-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 10 shows the OM-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.
code of 2048. Any deviation from this is an offset error. Figure 10 shows the OM-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 10 are drawn for clarity and are not drawn to scale.