triOS Dissolved Oxygen, Руководство по эксплуатации

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D01-903en201912 Manual Dissolved Oxygen
Calibration
// Dissolved Oxygen
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5 Calibration
The sensor is calibrated to specification at the factory. The manufacturer does not recommend calibration unless due to specific
local regulations. If calibration is required, let the sensor come to equilibrium with the measurement process before calibration.
Do not calibrate the sensor at setup.
After the membrane cap is replaced, calibration should always be carried out.
It is also advisable to regularly clean the sensor in a water-sulphite solution with a sulphite concentration of < 2 %, and to
subsequently check the zero point (0 % saturation).
If the zero point is moved, a complete two-point calibration must be carried out.
5.1 Two-Point Calibration
With two-point calibration, the zero point (0% - offset) and slope (100 %)of the sensor are calibrated. This calibration method
offers the greatest possible level of accuracy and is particularly recommended for measurements of small oxygen concentra-
tions.
It is carried out as follows:
5.1.1 Offset calibration
The sensor must be cleaned before calibration (see chapter 6). Immerse the sensor in a water-sulphite solution (sulphite con-
centration < 2 %) in order to determine the zero point (0 % saturation). Mix the solution with the sensor so that the saturation
in oxygen decreases more quickly (The oxygen fixed to the Membrane Cap must be consumed).
After calibration, clean the sensor with clear water and carefully dry it.
5.1.2 Slope calibration
Sensor slope is determined by positioning in oxygen-saturated environment (100 % saturation). The slope of the sensor is
calibrated beyond the defined state of 100 % oxygen saturation. This state can in principle be achieved in two ways:
1. By positioning the sensor in water vapor-saturated air (for example, directly over a water surface, see picture on
following page).
2. By positioning the sensor in air-saturated water (air is directed through water until the water is saturated with it).
The sensor can be damaged by chemicals. A damaged membrane can lead to incorrect measurement
results. The sensor membrane must not be in contact with the sulphite solution for longer than 15
minutes.
NOTICE
The sensor must be kept dry during the calibration process. Drops of water adhering to the sensor mem-
brane could distort the measurement.
The air pressure and temperature must remain constant during the calibration.