Delta OHM HD3409.2, Manual

Page: 13 / 40

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13
Measurement of the concentration of dissolved Oxygen
The probe must be calibrated periodically using the DO9709/20 (for polarographic probe) or
DO9709/21 (for galvanic probe) calibrator.
The instrument checks the dissolved Oxygen probe efficiency; the "CHNG MEMBRANE AND
ELECTROLYTE" message indicates that the probe is exhausted.
The same message is displayed during calibration: either when calibration is not possible or the
reading is unstable. It is thus necessary to replace the probe or clean the measurement cell with re-
placement of the electrolyte and/or the membrane covering the measurement electrodes.
Proceed as follows:
1. Connect the probe to the instrument.
2. Turn the instrument on with the ON/OFF key.
3. Wet the sponge contained in the calibrator using 2ml of distilled water.
4. Insert the probe into the calibrator.
5. Wait a few minutes until the system stabilizes thermally and 100%RH is reached inside the
calibrator.
6. Using "mg/l-%", select the measurement of dissolved Oxygen concentration (SAT%).
7. Press CAL to start the calibration: press ENTER to confirm and exit the procedure, or ESC
to quit the calibration without making changes.
8. On pressing ENTER, the display shows the new gain value (SLOP) for a few seconds and then
will progressively reach 101.7%.
The instrument is calibrated and ready for use.
On pressing ENTER during calibration, the instrument checks that the correction to be made does
not exceed the expected limits for correct functioning. Slope between 0.500 and 1.500. If the cali-
bration is rejected because it is outside the admitted corrections, the
CAL ERR message will ap-
pear, followed by the "CHNG MEMBRANE AND ELECTROLYTE" message. The instrument
maintains the previous calibration values until the probe's efficiency is restored.
Electrolyte solution and/or membrane replacement
The electrolyte contained in the dissolved Oxygen probe will be exhausted because of the chemical
reaction generated by the current in proportion to the partial pressure of the Oxygen present in the
water. Subsequently, the current generated by the probe is so low that the calibration operation is
impossible. It is necessary to replace the electrolyte contained in the probe to restore its functionality.
Incorrect use of the probe can cause the rupture or obstruction of the Oxygen-permeable membrane con-
taining the electrolyte solution. In this case it is necessary to replace the membrane and the electrolyte
solution.