Multi 3620 IDS Dissolved oxygen
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7.2.4 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.
7.3 Calibration
7.3.1 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.
7.3.2 When to calibrate?
If your evaluation of the FDO
®
Check procedure suggests a calibration
When the calibration interval has expired
When your accuracy requirements are especially high
Routinely within the framework of the company quality assurance
7.3.3 Calibration procedure
Calibration in water vapor-saturated air.
To calibrate the FDO
®
925 use the calibration and storage beaker.
The FDO
®
925 D.O. sensor ages so little it does not have to be reg-
ularly calibrated.
To detect changes of the sensor as early as possible, the FDO
®
Check procedure can be useful (see section 7.2).
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