Xylem LFOx1400_LFOx1400-ID - Manual (Page 17)

LFOx1400(-ID) Maintenance, cleaning, replacement
41 ba75523e04 07/2011
5.5 Checking the DO module for freedom from zero-current
The DO module is free from zero-current. Checking the module for freedom
from zero-current is only necessary in the case of malfunctions that cannot
be remedied by exchanging the electrolyte solution and membrane cap or by
cleaning the electrodes.
There are two possibilities to check the DO module for freedom from zero-
current:
 Measurement in a nitrogen atmosphere (recommended method)
 Measurement in a sodium sulfite solution according to DIN EN 25814/
ISO 5814.
Caution
If you check the sensor according to DIN EN 25814/ISO 5814, do not
leave the sensor in the sodium sulfite solution for more than 2 minutes.
Danger of sensor poisoning!
Test criterion The DO module is OK if the measuring instrument displays < 1 % DO
saturation after 2 minutes.
5.6 Aging of the conductivity measuring cell
Normally, the conductivity measuring cell does not age. Special measuring
media (e.g. strong acids and lyes, organic solvents) or too high temperatures
shorten the operational lifetime considerably or damage the measuring cell.
The warranty does not cover cases where such conditions cause failure or
mechanical damage.
Note
For measurements under high pressure the filling must be completely free of
air bubbles.
Readiness to
measure
After approx. 30 to 50 minutes, the sensor is ready for operation. Subse-
quently calibrate the sensor.
Note
If you want to measure very low DO concentrations (< 0.5 % saturation), we
recommend to let the sensor rest overnight and then calibrate it.