Optical dissolved oxygen sensors are popular because they do not consume oxygen and normally require less maintenance than electrochemical DO probes. However, correct calibration and membrane cap care are still essential for reliable data.

Short Answer

For zero-point calibration, use a 2 percent sodium sulfite solution and wait for the reading to stabilize. For slope calibration, use air-saturated water or a properly prepared moist membrane condition when the accuracy requirement is not extremely high. Keep the fluorescent membrane clean, moist when stored, and protected from scratches and sunlight.

Zero-Point Calibration in Practical Terms

Prepare a 2 percent sodium sulfite solution by dissolving sodium sulfite in water. Place the probe into the solution and wait about 3 minutes until the reading stabilizes before sending the calibration command.

The key is stability. If the reading is still changing, wait longer. A rushed zero calibration can cause poor low-oxygen performance.

Slope Calibration With Air-Saturated Water

Air-saturated water can be prepared by aerating fresh distilled water for more than 1 hour, then letting it stand for about 20 minutes. Place the sensor into the water and wait for the reading to stabilize before calibration.

For less demanding applications, users may also keep the membrane cap moist without water droplets and calibrate after the value becomes stable.

Membrane Cap Protection

The fluorescent membrane is the heart of the optical DO sensor. Do not touch it by hand, do not scratch it, and do not expose the inner surface of the fluorescent cap to sunlight. Avoid friction during testing, especially when the probe is used in tanks with suspended solids or near hard surfaces.

If scratches appear on the membrane cap, contact YexSensor for service instead of trying to polish the membrane.

Maintenance Advice for Field Users

A two-month maintenance interval is a good starting point for many sites. Rinse the sensor surface with clean water. If dirt remains, wipe gently with a damp soft cloth. For stubborn dirt on the outer body, a small amount of household washing liquid can be used in water.

When the sensor is not used, reinstall the protective cap and keep the sponge inside moist. Newly purchased sensors should be activated in tap water for 24 hours before use.

Related YexSensor PDF Guides

For calibration commands and model-specific handling notes, see the Water Quality Sensor Calibration and Usage Precautions PDF and the Water Quality Sensor Usage and Maintenance Instructions PDF.

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