Evaluation; Calibration; Why Calibrate; When To Calibrate - wtw Oxi 3310 IDS Operating Manual

Dissolved oxygen
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5.2.4 Evaluation

The evaluation is based on the accuracy required by the used. Together with
the nominal value (100 %) this results in a validity scope for the check.
If the measured value is within the validity scope, no cleaning or user
calibration is required.
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. sensors 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 3310 IDS (Oxi 3315) provides 2 calibration procedures:
 Calibration in water vapor-saturated air.
®
Use an OxiCal air calibration vessel for the calibration.
Oxi 3310 IDS (Oxi 3315)
® CHECK PRO
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