Problems may arise due to errors with:

  • Electrode function
  • Technique

Follow the steps below to isolate the source of the problem.

Electrode Function

Electrode function can be verified by testing the probe in an oxygen-free environment and a 100% air-saturated environment. The two methods described below may be used to prepare an oxygen-free solution.

Method 1:  Fill a clean beaker with distilled water. Bubble nitrogen gas through the water for 20 minutes. This will remove all oxygen from the water.

Method 2:  Fill a clean beaker with distilled water. Add sodium sulfite to the water while stirring until no more of the compound dissolves. This will remove the oxygen from the water.

Prepare an oxygen-free solution, and a 100% air-saturated environment (described in the Calibration section).  Then follow the procedure below.

1.      Connect the dissolved oxygen probe to the PC via the USB connector.

2.      Let the dissolved oxygen probe warm up for 15-30 minutes.

3.      During the warm-up time in step 2, place the dissolved oxygen probe in the oxygen-free solution (Method 1 or 2 above).

4.      After the probe has warmed up for 15-30 minutes in the oxygen-free solution, record the % saturation value.

5.      Place the probe in a 100% oxygen-saturated environment (described in Calibrating WQ-DO Dissolved Oxygen Smart USB Sensor).

6.      Wait for the readings to stabilize, and record the % saturation value.

If the electrode does not read near 0% or near 100% in the respective solutions, polish the electrode following the instructions in WQ-DO Dissolved Oxygen Smart USB Sensor Maintenance. Prepare new solutions, and repeat the test.

If the electrode percentages are still outside the normal range after this procedure, the probe may need to be sent to NexSens for evaluation.

Technique

  • Closely follow the methods described in WQ-DO Dissolved Oxygen Smart USB Sensor Measurement Techniques.
  • Closely inspect the membrane for any punctures, tears, or fouling.
  • Replace DO electrolyte solution in cap with new solution.
  • Check for deposits on silver anode or platinum cathode.  Polish following the instructions in WQ-DO Dissolved Oxygen Smart USB Sensor Maintenance.
  • Recalibrate.  Calibrate at a temperature within 10º C of the sample temperature.  Make sure the correct barometric pressure is entered.  Adjust salinity value as needed.
  • Make sure to stir the probe continuously to provide fresh oxygen to the probe surface.

 

REV: 13H17

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