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It is recommended to calibrate the probe frequently, especially if high accuracy is required.
The DO probe should be recalibrated:
• Whenever the DO probe is replaced.
• At least once a week.
• Before BOD, OUR, SOUR measurements.
• When calibration reminder is activated (“DO Cal Expired”).
• If the readings are far from the calibration point.
Note: BOD, OUR and SOUR readings are automatically derived from the DO readings. Calibrate
in DO mode.
The following options are available for the Dissolved Oxygen calibration:
• Two point calibration at 100 and 0% Saturation.
• Single point at 0% Saturation.
• Single point at 100% Saturation.
• Single point user calibration using a standard value set by the user in % saturation, mg/L or ppm.
When automatic calibration is performed it is assumed that the standard value is 100% water saturated
air and 0% Saturated solution.
When a user calibration is performed it is assumed that the standard value is the DO value at the
current pressure, temperature and salinity.
Initial preparation
Make sure the probe is ready for measurements, i.e. the membrane is filled with electrolyte and the
probe is connected to the meter and polarized.
For an accurate calibration, it is recommended to wait for at least 15 minutes to ensure precise
conditioning of the probe.
Remove the protective cap from the DO probe.
Make sure the salinity value has been set to the salinity of the standard if user concentration standard
is employed.
Probe conditioning
The probe is polarized with a fixed voltage of approximately 800 mV between the cathode and
anode. Probe polarization is essential for stable measurements. With the probe properly polarized,
oxygen is continually consumed as it passes through gas permeable PTFE membrane.
If polarization is interrupted, the electrolyte solution continues to be enriched with oxygen until it
reaches an equilibrium with the surrounding solution. Whenever measurements are taken with a
non-polarized probe, the measurement will be drifty and inaccurate. The measurement will jump
when the probe is moved.
DO CALIBRA
TION
