Tech Note 1266 Detail

Optical Dissolved Oxygen (ODO) Troubleshooting

Affected Products:

PS-2196 PASPORT Optical Dissolved Oxygen Sensor
PS-2230 Advanced Water Quality Sensor

Problem/Symptom:
Optical Dissolved Oxygen (ODO) Troubleshooting

PASCO Solution:

How do I measure?

  1. Check that the cap at the end of the probe is screwed on tight, has most of the black paint intact, and is clean, hydrated, and calibrated.
  2. If using the probe in field conditions, screw on the Optical Dissolved Oxygen Sensor Metal Guard - PS-2588.
  3. Connect the probe to a powered PASPort interface.
  4. Immerse the probe in the solution to be measured.
  5. Monitor or record the value in the data acquisition software.
  6. Wait for the probe to give a response that is stable within 0.5% under controlled conditions or a minimum of 100 seconds under uncontrolled (field) conditions.
  7. Stop data recording/monitoring.
  8. Start recording again to collect valid data.

The value has not stabilized after more than five minutes?

The sensor cap may have dehydrated. Follow the directions to rehydrate. If you still experience problems, remove the cap, and clean and dry both the sensor lens and the inside of the cap. Check that the o-ring is intact and replace the cap so that it is finger tight. If that does not work, replace the cap.

How do I store the probe?

Clean and disinfect the sensor cap and insert the probe completely in the black vinyl sleeve with a moistened sponge in the bottom.

What type of calibration is recommended?

The dissolved oxygen sensor may be used without calibration, but a one-point slope calibration at 100% dissolved O2 saturation is recommended for best results:

  1. Remove the black sleeve from the dissolved oxygen probe and check that the sponge is still moist. (One can do this by inverting the cap and squeezing the sponge with a capped pen to see if any water comes out or by pressing the sponge with a cotton swap and then checking whether the swap is wet.)
  2. If the sponge is completely dry, resaturate the sponge, invert the black sleeve (to retain the water vapor), and rehydrate the membrane sensor cap.
  3. Without touching the probe with your fingers, check that the probe cap is clean and moist.
  4. If the probe cap has an odor or is visibly contaminated, follow the instructions to clean and disinfect the probe.
  5. Gently blot off any water droplets with a lens cloth.
  6. Slide the protective black sleeve to the ridges of the probe. (Do not slide the probe cap any further in order to prevent hyperbaric conditions, which can result in a 3% error.)
  7. Begin monitoring or recording.
  8. When the value stabilizes to within 0.1% of a value (2-5 minutes), calibrate the sensor at 100% saturation, as shown in the PS-2196 manual.

What if I calibrated the probe incorrectly?

If you performed a one point calibration incorrectly, simply repeat it; however, if you performed a 2-point calibration incorrectly, it will typically be easier to restore the factory calibration and perform the recommended 1-point slope calibration.

How do I restore the Factory Calibration?

Restore Calibration with Cap Coefficients (PASCO Capstone)

  1. Go to Tools palette.
  2. Select Hardware Setup.
  3. Click on the sensor icon of the optical dissolved oxygen sensor.
  4. Click the blue properties sprocket.
  5. Re-enter the Cap Coefficients from the information included with the cap.
  6. Click OK.

Restore Calibration to Factory Default Without Cap Coefficients (PASCO Capstone)

  1. Go to Tools palette.
  2. Click on Calibration.
  3. Select Saturation.
  4. Select Next.
  5. Select Restore Factory Calibraion.
  6. Click Next.
  7. Click Finish.
  8. Select Saturation

What is the expected life of the sensor membrane cap?

We expect the sensor cap to last 1-3 years in an educational environment. Replacement caps can be purchased as Optical Dissolved Oxygen Sensor Cap - PS-2587.

How do I clean and disinfect the probe?

  1. Fill a 100 mL beaker with 30-40 mL of 3% hydrogen peroxide.
  2. Add a drop of dish detergent.
  3. Agitate the probe in the solution until the probe is clean.
  4. If necessary to remove visible fouling, gently wipe the probe with a lint-free tissue wetted with the cleaning solution.
  5. Soak the probe for 20-30 minutes in the solution.
  6. Rinse with clean tap water.
  7. Use or store the probe. (Do not let the probe dry out.)

How do I rehydrate the membrane cap?

  1. Wet the sponge in the cap and invert the cap to retain the water vapor. (Obtaining water-saturated air requires at least 15 minutes at room temperature.)
  2. Soak the sensor cap for 24 hours in warm (25 - 40 C) tap water.
  3. Recalibrate and use immediately, or store properly.

How do I replace the sensor cap?

Refer to the PS-2587 manual.

Creation Date: 01/26/2015
Last Modified:
Mod Summary: