Siemens SIMATIC ET 200AL System Manual page 2055

What you should know about analog technology
2.7 Operational and basic error limits
Basic error limit
The basic error limit is the entire measurement or output error rate in the rated range at an
ambient temperature of 25 °C and temperature-settled state.
The basic error limit of the module is more or less a theoretical value, because a constant
ambient temperature of 25 °C is rarely maintained in plants. For this reason, the operational
limit always takes priority in terms of the practical selection and assessment of a module.
Note
The operational limit and basic error limit percentages listed in the technical specifications
always relate to the maximum possible I/O value (the measuring range end value) in the
rated range of the module.
The following image shows an example of operational and basic error limits in comparison
with the ideal curve.
Figure 2-13
24
Operational and basic error limits
Analog value processing
Function Manual, 06/2014, A5E03461439-AC