Xylem MPP 350 - Manual (Page 20)

Maintenance, cleaning, replacement MPP 350
20 ba75434e02 07/2005
5.5 Checking the D.O. module for freedom from zero-current
The D.O. 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 D.O. 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 D.O. module is OK if the measuring instrument displays < 1 % D.O.
saturation after 2 minutes.
5.6 Aging of the probe
Except for the pH electrode, the probe does not naturally age when used
according to instructions. Special measuring media (e.g. strong acids and
lyes, organic solvents) or too high temperatures shorten the operational
lifetime considerably or damage the probe. 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 mea-
sure
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 D.O. concentrations (< 0.5 % saturation), we
recommend to let the sensor rest overnight and then calibrate it.