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6.4.2 Calibration due
Calibration due is the date when the calibration must be done next according to the settings
of the calibration interval. The calibration intervals are set by the Yokogawa HOST system,
for details see the belonging User’s Manual.
6.4.3 Last calibrated
The last calibrated is the date on which the last sensor calibration was performed. For cell
constant the displayed value is date of this last calibration.
6.4.4 Predictive maintenance
Predictive sensor maintenance predicts the date when the sensor will need recalibrating for
maintaining measurement accuracy.
The date is the based upon the two sensor characteristics:
•
Polarization
, checked every 24 hours. The function predicts the date when the
measurement value will cross the upper limit set by the Yokogawa HOST system, and
indicates the date and its reliability status. The date is predicted based on the intersection
point of the theoretical lower limit (0%) and the upper limit, and the extrapolated line of the
values obtained by the least squares method.
•
Historical calibration data of cell constant
by analyzing the historical data of cell
constant obtained by calibration. The function predicts the date when a new calibration
will lead to a crossing of the upper limit or lower limit set for a difference (in percentage)
in between the actual cell constant and the calibrated factory cell constant. The date is
predicted based on the intersection point of the lower limit and the upper limit, and the
extrapolated line of the values obtained by the least squares method.
The date is predicted based on the best status of correlation in those two parameters. If
some parameters have the same status, the nearest date is selected. The function indicates
the date and its reliability status.
Figure 6.1: Predictive sensor maintenance date
6.4.5 Sensor wellness
The SA11 can calculate the performance status of the sensor connected. The calculated
result depends on user programmable settings done by the Yokogawa HOST system, and
the sensor diagnostics data stored in the ID-chip of the sensor.
When a sensor is replaced or exchanged, a reset of the wellness data is not necessary. If a
user wants to reset this data anyhow, this is possible by the Yokogawa HOST system. For
details see the belonging User’s Manual.
There are five (5) different wellness statuses for SC:
•
Cell constant
•
Polarization
•
Progress time
, the time in between 0 and actual operating hours of the sensor.
•
Heat cycle
counter which counts the settable temperature step changes (up or down) of
a sensor.
•
Total
indicating the worst wellness state of those activated.