YOKOGAWA EXA DO402G, Руководство пользователя

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<6. Calibration Procesure>
6-4
IM 12J05D02-01E
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 approximately 50 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
It takes a long time to calibrate the DO30G sensor or other galvanic sensors and polarographic
sensors with sulfite-saturated water. Even after CAL.END is displayed, wait 40 to 50 minutes
and then press the YES key. If the YES key is pressed without waiting, the indicator may
show a minus reading during measurement. In an aerobic tank with high dissolved oxygen
concentrations, a zero calibration is not required if a zero check is performed, because the
indicating error is so insignificant that it does not affect the measurement results. There will be no
problem if the electrodes are immersed in a zero solution for about 10 minutes and the indication
falls below 1 mg/L. However, it is recommended to wait for about 60 minutes before performing
a zero calibration when a new sensor is installed, when the membrane is replaced, or in a place
where dissolved oxygen concentrations are low, such as in an anaerobic tank. If the solubility
does not fall below 1 mg/L even after waiting for about 10 minutes, remove the sensor and clean
it, and replace the membrane and/or replace the electrolyte solution.
Calibration may take longer than 10 minutes. Before starting the calibration procedure, check the
setting of Auto Return (*RET.) in Service Code 50. It is recommended to set the Auto Return to
“0” (No return to meas. from HOLD). After the calibration procedure has been completed, set the
Auto Return to the desired setting in Service Code 50.
9th Edition: Aug. 05, 2015-00