How To Measure Dissolved Oxygen In Water

We manufacture Dissolved Oxygen (DO) parameter electrodes for measuring and monitoring Dissolved Oxygen in all water types including fresh, brackish and salt water locations. For more information on our Aquaprobes, head over to our product page for the full range.

This page will give you an insight into how to measure Dissolved Oxygen in water with Aquaread’s dedicated equipment.

Our Dissolved Oxygen Electrodes are very sensitive, they can detect small changes with incredible precision. It can measure between 0 – 500.0% Saturation / 0 – 50.00 mg/L.

Dissolved Oxygen Range 0 – 500.0% / 0 – 50.00 mg/L
Resolution 0.1% / 0.01mg/L
Accuracy 0 – 200%: ± 1% of reading. 200% – 500%: ± 10%

We provide two different types of dissolved oxygen sensor Dissolved Oxygen sensor; Galvanic DO and Optical DO. Galvanic sensors are found on the AP-700 and AP-800 Aquaprobes, whereas the more advance optical sensors are found on the AquaPlus, AP-2000, AP-5000 and AP-7000 Aquaprobes.

Galvanic

Rugged Galvanic DO

This is the classic way to measure dissolved oxygen. The sensor uses a permeable membrane that allows oxygen to pass through. Once the oxygen is inside the sensor it reacts wit the electrolyte solution that is inside the cap. This creates a current that can be measured. Whilst this sensor is available at a lower cost it does require a little more maintenance. Regular cap and electrolyte changes are required to keep the sensor running well along with frequent calibration.

Optical

optical DO sensor

The optical sensor works on the principle of luminescence quenching. It is a more modern method of dissolved oxygen measurement. This kind of sensor has a number of benefits, including less calibration frequency, 2+ years cap life and no flow of water required as oxygen is not consumed across the membrane, making it better for long deployments.

The DO sensor comes combined with our Electrical Conductivity sensor which features four stainless-steel rings.

Preparation For Taking DO Measurements

All probes from Aquaread are supplied with the DO cap (galvanic or optical) fitted and fully calibrated at the factory, so this sensor is ready to use straight out of the box. We recommend that galvanic sensors are subsequently, fully calibrated ever month. Optical sensors should have their 0% calibration point calibrated every 6 months.

Calibrate the probe

  1. Before each day’s use, the 100% saturation point should be checked in moist air and re-calibrated if necessary. For optimum accuracy, calibrate the DO 100% point as near to your sample temperature as possible (within the calibration temperature limits of 5°C – 40°C). If you are going to calibrate both the Zero and 100% points at the same time, always calibrate the Zero point first, then the 100% point.

  2. Pour 200mL of DO Zero calibration solution into a calibration cup, wash the Probe in distilled water, then gently lower the sleeved Probe into the cup all the way. Tap the probe against the bottom of the cup several times to dislodge any air bubbles.

  3. Turn the Aquameter on and wait until the temperature and DO measurements are completely stable. Press Menu and select ‘Calibration’. Press OK on the ‘Full Cal’ option. Press OK and select ‘DOZero?’ to set the Zero point.

  4. The top line will display a value which represents the health of the luminophore. This value should be between 3.5 and 4.5 (at 25°C). If the value returned is less than 3.5, the Optical DO Cap should be replaced.

  5. To calculate the 100% point, the probe needs to be washed thoroughly in fresh water, then shaken off to ensure no droplets remain on the DO membrane. Moisten a clean cloth or piece of tissue paper with fresh water and wrap it around the open end of the probe ensuring all the holes are covered. Place the probe on a flat surface. Do not hold the probe as the heat from your hands will warm the probe up and interfere with calibration.
  6. Switch the Aquameter on and wait until the temperature measurement is completely stable – this is very important. Select ‘DO100%’ as your calibration option and wait for it to complete.

  7. The top line on the results screen represents the same as when calibrating the Zero point, except the value should be between 0.8 and 1.5 (at 25°C). If the value returned is less than 0.8, again the Optical DO Cap should be replaced. Be sure to note down the value in the probe’s calibration record book.

 Logging options

All Aquaread packages are supplied with our GPS Aquameter for portable data collection. We also manufacture different data logging devices to ensure you have the best choices when it comes collecting your data for analysis. You can find these over on our Logging Options page, where we also have video introductions to them.

Get in touch with Aquaread today

Find out more about how to measure Dissolved Oxygen in water or get further support by getting in touch with us via our contact form on this page or giving us a call on +44 8442 221 206. Full details are available on our contact page.

Download one of our comprehensive product manuals for more instructions and information on our DO measuring equipment.

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