Siemens SIMATIC ET 200AL, System Manual

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What you should know about analog technology
2.6 Repeat accuracy
Analog value processing
22
Function Manual, 06/2014, A5E03461439-AC
2.6 Repeat accuracy
Definition
The repeat accuracy is the maximum deviation in measured/output value for the same input
signal or output value after another value has been created or output. Other parameters, e.g.
the Temperature parameter, remain unchanged. The repeat accuracy refers to the rated
range of the module and applies in a steady temperature state.
Measured value variance
The repeat accuracy provides information on the variance of individual measurements. The
smaller the variance, the greater the repeat accuracy. The repeat accuracy is therefore one
of the most important properties of measuring devices. In the technical data, the repeat
accuracy is given as a percentage of the input or output range at 25°C in the steady state.
Example
The specified repeat accuracy for an analog input module as a percentage of the measuring
range end value is ±0.02 %. This corresponds to a repeat accuracy of 2 mV for any value
within the measuring range of ±10 V. If you change the measured value from 10 V to -10 V,
for example, and then measure with 10 V again, the measured value deviation may not
exceed ±2 mV.
①
Good repeat accuracy
②
Poor repeat accuracy
Figure 2-12 Repeat accuracy of measured values output