Siemens SIMATIC ET 200AL, System Manual

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Analog value processing
106
Function Manual, 06/2014, A5E03461439-AC
Supported functions
7
7.1 Calibrating analog modules
7.1.1 Overview
Calibration
A calibration checks the process values measured by the analog input module and the
process values output by the analog output module, determines the deviation from the actual
values and compensates for any measurement and output errors.
Calibrating analog modules
The SIMATIC analog modules were calibrated before being shipped and have excellent
long-term stability; calibration is therefore not required during runtime.
But certain regulations and directives, for example from the Food and Drug Administration
(FDA), require regular calibration for all components in a measuring circuit. These
components include analog input and output modules.
A calibration makes sense especially for plants in which sensors detect and process
relatively small voltages or currents. The calibration compensates for influences on the
measuring result by cables and/or temperature.
The calibration collects the new values and saves them retentively on the module. But the
calibration values determined prior to delivery at the plant are not lost. You can return to
these original calibration values at any time.
Note
The calibration saves the calibration values of each channel for the specific measuring range
retentively on the module, which means the values apply to the same measuring range in
which the user calibration took place.
If you reconfigure a channel with effective user calibration values to another type of
measuring mode, the calibration values saved at the plant for this channel and for this
measuring range will become effective.
But the user calibration values are not deleted. They are not overwritten until there is a new
user calibration of the channel. If you set the original measuring range for this channel once
again without new user calibration, the previously determined user calibration values will
become effective.