Analog Modules
4-34
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
4.5.3 Effect of Operational Limit and Basic Error Limit
Operational limit
The operational limit is the measuring error or output error of the analog module
over the entire temperature range authorized for the module, referred to the rated
range of the module.
Basic error limit
The basic error limit is the operational limit at 25 °C, referred to the rated range of
the module.
Note
The percentage details of operational and basic error limits in the technical
specifications of the module always refer to the highest possible input and output
value in the rated range of the module.
Example of determination of the output error of a module
An analog output module SM 332; AO 4 x 12 bits is being used for voltage output.
The output range from “0 to 10 V” is being used. The module is operating at an
ambient temperature of 30 °C. Thus the operational limit applies. The technical
specifications of the module state:
• Operational limit for voltage output: "0.5 %
An output error, therefore, of "0.05 V ("0.5% of 10 V) over the whole rated range
of the module must be expected.
This means that with an actual voltage of, say, 1 V, a value in the range from 0.95
V to 1.05 V is output by the module. The relative error is "5 % in this case.
The figure below shows for the example how the relative error becomes
increasingly less the more the output value approximates to the end of the rated
range of 10 V.
"0.05 V
1 V0 V
"0.05 V
Output Value
"0.05 V
8 V
10 V
* Operational limit
–1 V
(¢ "0.5 %*)(¢ "0.625 %)(¢ "5 %)
Figure 4-3 Example of the Relative Error of an Analog Output Module
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