Chapter 6
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Using the DO/RDO Channel
Dissolved Oxygen Calibration Procedure
Note: A polarographic dissolved oxygen sensor must be polarized prior to use. The
polarographic dissolved oxygen sensor is continuously polarized when connected to the meter.
If the polarographic dissolved oxygen sensor is new, has been serviced or has not been
connected to the meter – connect the sensor to the meter, power on the meter and wait 30
minutes for the sensor to polarize.
Orion Star A223 RDO/DO meters can perform the following calibrations:
•
Air (water-saturated air) – This is the simplest and most accurate method and uses the
calibration sleeve included with most dissolved oxygen sensors. For best accuracy, the
calibration temperature should match the expected sample temperature. Moisten the
sponge in the calibration sleeve with distilled water and insert the sensor into the sleeve.
Alternatively, a BOD bottle can be used with just enough distilled water to cover the bottom
without touching the sensor.
•
Water (air-saturated water) – This method uses water that is 100% saturated with air.
Bubble air into a water sample for an extended period, preferably overnight.
•
Manual (Winkler) – This method uses a water sample with a known concentration of
dissolved oxygen and is typically used to calibrate the DO sensor to the value achieved by
a Winkler titration. Due to possible titration errors, this method is inherently less accurate.
•
Set Zero – This method uses an oxygen free solution to add a zero point to an existing
Water Saturated Air or Air Saturated Water calibration. This calibration is generally
recommended when measurements are below 10% saturation or 1 mg/L.
Prepare the dissolved oxygen sensor according to the instructions in the sensor manual.
Connect all sensors to be used to the appropriate meter inputs.
Make sure the meter measurement mode is set to dissolved oxygen (DO or RDO).
Thermo Scientific
Orion Star A220 Series Portable Meter User Manual
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Summary of Contents for Orion Star A220 Series
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