5.6.4
Effect of operational limit and basic error limit
Operational limit
The operational limit represents the measuring error, or output error, of an analog module
across the entire permissible temperature range of the module, based on the module's nominal
range.
Basic error limit
The basic error limit represents the operational limit at 25° C, based on the module's nominal
range.
Note
The percentage details of operational and basic error limits in the specifications of the modules
always refer to the highest possible input and output value in the nominal range of the module.
In the ± 10 V measurement range this would be the 10 V.
Example of determination of the output error of a module
An analog output module SM 432; AO 8 x 13 Bit is being used for voltage output. An output
range of "±10 V" is set. The module is operating at an ambient temperature of 30° C, i.e. the
operational limit applies. The specifications of the module state:
● Operational limit for voltage output: ±0,5 %
Hence, an output error of ±0.05 V (±0.5 % of 10 V) across the nominal 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.
For the example, the figure below shows how the relative error decreases as the output value
approaches the end of the 10V range.
1
( ±0,5
%
*)
1 V
0 V
( ±0,625
%
)
( ±5
%
)
8 V
10 V
-1 V
±0,05 V
±0,05 V
±0,05 V
=
^
=
^
=
^
Figure 5-1
Example of the relative error of an analog output module
*
Operational limit
(1)
Output value
Analog modules
5.6 Behavior of the analog modules
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
195
