User`s guide

DO700 V1.0 8/09
20
Zero Dissolved Oxygen Calibration
The meter receives a zero oxygen calibration before leaving the factory and only
requires a zero oxygen calibration when the electrode (or the electrode cap) is replaced
or has been in use for a relatively extended period of time (6 months or longer). To
perform a zero oxygen calibration:
1. Prepare 100mL of anaerobic water: In a 100 mL beaker add 5g anhydrous sodium
sulfite (Na2SO3) to 100 mL distilled water. Stir to dissolve. The anaerobic water will
be usable in 24 hours.
2. Polarize the DO electrode by connecting it into meter for 15 minutes and then
perform a standard calibration as described in the calibration section earlier in this
manual.
3. Place the electrode in the anaerobic water and press the CAL key to enter the
calibration mode. When the displayed value is ≤ 0.15mg/L (≤5min) press the
ENTER key.
4. If the displayed value is ≤0.02mg/L (within 5 minutes), this indicates that the
response time and the residual current are normal and there is no need to perform
the zero oxygen calibration, press the ENTER key to the normal operating mode.
5. If the displayed value is >0.15 mg/L after 5 minutes, this indicates that the
response time of the meter is too slow and there is too much residual current. In
this case, replace the membrane cap or remove the membrane cap and use the
supplied polishing paper to lightly wipe the gold plane’s cathode (the surface along
the gold-polished arc) and clean the surface of the cathode with a soft cloth or
tissue. Clean the electrode with distilled water and shake off the excess water. Add
some electrolyte to the membrane cap, re-assemble, and then perform a full scale
and a zero oxygen calibration.
Salinity Calibration
Under normal circumstances, a salinity calibration is not required. The meter is equipped
with an automatic salinity compensation; In addition, a salinity calibration has been
performed at the factory prior to shipment; however a salinity calibration is required
when the electrode is replaced or has been in service for a relatively extended period of
time. Refer to parameter P2 in previous section for calibration procedure.
Barometric Pressure Setting
The meter is equipped with a manual barometric pressure adjustment. It is
recommended that the value be set according to the standard barometric pressure table
when there is an excessive change in barometric pressure while using meter. This
ensures the accuracy of the barometric pressure compensation. To change the
barometric value refer to parameter P3 in the previous section. Use the Table in
Appendix C for barometric pressure values.