Endress+Hauser Memosens COS81D, Руководство по эксплуатации, Страница: 23 / 48

Memosens COS81D Calibration and adjustment
Hauser 23
2. If necessary:
Adjust the sensor to the zero point.
The reference method (sample calibration in zero point) can also be used here if
appropriate collecting vessels or reference measurement are available.
If the oxygen sensor is calibrated too early, this can result in an incorrect zero point.
Rule of thumb: operate the sensor for at least 30 min in the COY8 zero-point gel.
Follow the instructions in the kit documentation enclosed with the COY8 zero-point
gel.
7.3 Calibration in oxygen with 100% rH
1. Activate the hold status at the transmitter.
2. Remove the sensor from the medium.
3. Clean the outside of the sensor carefully with a damp cloth.
4. Suspend the sensor just above the surface of the water.
Do not immerse the sensor.
5. Allow a temperature compensation time of approx. 20 minutes for the sensor in the
ambient air. Make sure that the sensor is not exposed to any direct ambient effects
(direct sunlight, drafts) during this time.
6. Is the measured value display on the transmitter stable:
Perform the calibration in accordance with the Operating Instructions for the
transmitter. Pay particular attention to the software settings for the stability criteria
for calibration and for the ambient pressure.
7. Where necessary:
Adjust the sensor by accepting the calibration data.
8. Then place the sensor back into the medium.
9. Deactivate the hold status at the transmitter.
‣
Follow the calibration instructions in the Operating Instructions for the transmitter
used.
The constants Ksv and Tau0 of the Stern-Volmer equation are determined at both
calibration points (point in oxygen and zero point). The calibration quality index
provides an indication of the quality of the calibration in relation to the first reference
calibration of the spot cap. Therefore it is important to run the Change sensor cap
command in the calibration menu of the transmitter before every initial calibration of
a spot cap.
7.4 Calculation example for the calibration value
As a check, you can calculate the expected calibration value (transmitter display) as shown
in the following example (salinity is 0).
1. Determine the following:
• Ambient temperature for the sensor (air temperature in the case of the Air 100% rh or
Air variable calibration methods, water temperature in the case of the H2O air-
saturated calibration method)
• The altitude above sea level
• The current air pressure (= relative air pressure based on sea level) at the time of
calibration. (If indeterminable, use 1013 hPa.)
2. Determine the following: