Calibration; Why Calibrate; When To Calibrate; Calibration Procedures - wtw Oxi 3315 Operating Manual

Dissolved oxygen
28
If the measured value is outside the validity scope, the sensor shaft and
membrane should be cleaned, and the check should then be repeated
(see section 5.4.1).
Example:
– Required accuracy: ± 2 %.
– In water vapor-saturated air or air-saturated water, the nominal
value for the relative D.O. saturation (abbreviated: saturation) is
100 %.
– Therefore, the validity scope is 98 ... 102 %
– The check resulted in a measured value of 99.3 %
The measurement error is within the specified validity scope.
No cleaning or user calibration is required.
5.3

Calibration

5.3.1 Why calibrate?

D.O. probes age. This changes the slope of the D.O. sensor. Calibration deter-
mines the current slope of the sensor and stores this value in the instrument.
The FDO ® 925 D.O. sensor ages so little it does not have to be
regularly calibrated.
To detect changes of the sensor as early as possible, the FDO ®
check procedure can be useful (see section 5.2 FDO
, page 26).
CEDURE

5.3.2 When to calibrate?

 If your evaluation of the FDO ® check procedure suggests the necessity of
a calibration
 When the calibration interval has expired
 When your accuracy requirements are especially high
 Routinely within the framework of the company quality assurance

5.3.3 Calibration procedures

The Oxi 3315 provides 2 calibration procedures:
 Calibration in water vapor-saturated air.
®
Use an OxiCal air calibration vessel for calibration.
 Calibration via a comparison measurement (e.g. Winkler titration according
to DIN EN 25813 or ISO 5813). At the same time, the relative slope is
adapted to the comparison measurement by a correction factor. When the
correction factor is active, the [Factor] indicator appears in the measuring
screen.
Oxi 3315
®
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CHECK PRO
ba75944e02 03/2012