A Brief Guide to Cleaning Dissolved Oxygen Auto-Analyzer Sensors

Regular cleaning of the sensor (probe) is essential for maintaining the accuracy and reliability of your dissolved oxygen (DO) auto-monitoring system. Biofouling (accumulation of algae, bacteria, slime) and sediment can quickly degrade sensor performance. Always consult your specific instrument's manual first, as procedures can vary.

Important Safety Precautions:

• Power Down: Before cleaning, safely power down the instrument or isolate the sensor according to the manufacturer's instructions to prevent electrical hazards or damage.

• Handle with Care: The sensor membrane is delicate. Avoid scratching, poking, or applying excessive pressure to it.

Cleaning Materials:

• Soft cloth or sponge

• Mild detergent or soap solution

• Lukewarm water

• Soft-bristled brush (e.g., old toothbrush)

• For stubborn deposits, a dilute bleach solution (e.g., 1-part household bleach to 10-parts water) is sometimes recommended – check your manual first as some materials may be incompatible.

Step-by-Step Cleaning Procedure:

1. Remove the Sensor: Carefully remove the sensor from its mounting in the water body or flow chamber.

2. Initial Rinse: Gently rinse the sensor tip with lukewarm water to remove loose debris and sediment.

3. Gentle Wiping: Using a soft cloth or sponge dampened with clean water, gently wipe the entire body of the sensor to remove any buildup. Avoid harsh scrubbing on the sensor tip.

4. Cleaning the Membrane Cap: Pay special attention to the semi-permeable membrane cap at the tip.

• Use a soft cloth very gently to wipe the membrane surface.

• For crevices or threads, a soft-bristled brush can be used carefully to dislodge debris.

• If biological fouling is evident (slime, algae), carefully clean the membrane cap using the mild soap solution or the dilute bleach solution if approved for your sensor. Ensure no liquid enters the vents or holes around the sensor body.

5. Final Rinse: Thoroughly rinse the entire sensor, especially the membrane cap, with clean, lukewarm water to remove any traces of detergent or cleaning solution. Residual cleaner can damage the membrane or affect readings.

6. Reinstall and Check: Reinstall the sensor securely. Power the instrument back on.

Post-Cleaning Consideration: Calibration
Cleaning can slightly alter the sensor's characteristics. It is highly recommended to perform a calibration after cleaning the sensor to ensure subsequent readings are accurate. Follow your manufacturer's calibration procedure.

Frequency:
The cleaning frequency depends entirely on the fouling potential of the water body. Fast-fouling environments might require weekly cleaning, while cleaner waters might only need monthly attention. Let your observed data quality and manufacturer recommendations guide your schedule.

If the membrane is damaged, scratched, or deeply stained, or if the sensor continues to give unstable readings even after proper cleaning and calibration, the membrane cap (and possibly the electrolyte inside) likely needs replacement according to the manufacturer's instructions.