YSI IQ SensorNet 2020 XT Terminal - Manual (Page 169)

System 2020 XT USB What to do if ...
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When this number is reached, no further IQ sensor can be installed. If
necessary, an inactive dataset has to be erased to make an extension
possible.
Note
The current calibration data of the IQ sensor is always stored in the
sensor. If an IQ sensor is connected that is ready for operation and
calibrated, it can be used immediately without the need for
recalibration.
Note
To erase inactive datasets, see section 5.5.3.
If an IQ sensor is connected to the system when an inactive dataset is
present, the following cases are possible:
Case 1:
The serial number of the
IQ sensor is identical with the
serial number of an inactive
dataset. The connected IQ sensor is
automatically assigned to the
inactive dataset and starts to
operate again.
Example: Maintenance or repair.
This mechanism ensures that all
IQ sensors retain their settings
and links if an IQ sensor was
removed for maintenance, or if
the system was temporarily
switched off.