YOKOGAWA EXA DO402G, Instruction Manual

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IM 12J6B3-E-H
6-3. Calibration procedure using water calibration method
6-3-1. Preparation
Move the sensor to a maintenance site and wash off any dirt on the membrane. Lightly wipe off any
remaining water from the membrane with a soft tissue.
Prepare the necessary equipment and reagents to be used for the span and (if required) zero calibration.
Equipment for span calibration includes:
• beaker or bucket
• magnetic stirrer or other means of agitating the water
• Demineralized water or salty process water if salinity compensation is activated
• Air supply pump (aquarium pump)
• Glass diffuser to generate small air bubbles
NOTE:
It takes 15 to 30 minutes of aeration before it can be assumed that the water is fully saturated with air.
Reagent for zero calibration:
• Sodium sulfite
• demineralized water
The zero oxygen solution contains 20- 30 grams of sodium sulfite per liter.
6-3-2. Calibration operation (water calibration method)
If both zero and span calibration are used, it is better to start with span calibration in spite of normal
calibration sequence with analog instrumentation. Otherwise the sensor must be rinsed off carefully to
prevent ingress of oxygen absorbing sulfite in the aerated water.
NOTE:
Zero calibration in the sodium sulfite solution takes a long time. Even after CAL.END prompt it is necessary
to wait 40-50 minutes before zero adjustment can be made. Otherwise calibration errors are introduced in
the measurement. It is recommended not to do a zero calibration, but a zero check only. A good clean
sensor does not have a zero current and does not require zero calibration. If the sensor has a substantial
zero current, the sensor has to be disassembled, cleaned and filled with fresh electrolyte solution and new
membrane has to be fitted.
6-4 Calibration