Xylem FDO 925 - Manual (Page 12)

Maintenance, cleaning, replacement FDO
®
925
28 ba75898s01 04/2010
Note
If the sensor cap is visibly damaged it has to be replaced.
3.4 Checking the zero point of the sensor
There are two methods to check the zero point of the sensor:
z Measurement in a nitrogen atmosphere (recommended method)
z Measurement in a sodium sulfite solution according to DIN EN 25814/
ISO 5814.
Test criterion The sensor is OK if the measuring instrument displays < 0.5 % D.O.
saturation after 15 minutes.