Memosens COS81D is a digital oxygen sensor used for dissolved oxygen measurement. When paired with the Liquiline CM44x transmitter, it enables plug-and-play functionality and high-precision calibration. Proper calibration is a key step to ensure accurate measurement data and extend sensor lifespan. This article is intended for engineering technicians and procurement personnel and systematically introduces its calibration process and precautions.
I. Pre-Calibration Preparation
Before calibration, confirm that the sensor and transmitter are properly connected, and prepare the standard media and environmental conditions required for calibration.
- Check sensor status: Confirm that the fluorescence cap is not damaged or contaminated, and the membrane surface is clean.
- Confirm transmitter version: The Liquiline CM44x firmware must support the Memosens protocol.
- Environmental requirements: The calibration temperature should be stable, avoiding strong airflow and direct sunlight.
- Standard media: Use saturated humid air for air calibration; use oxygen-free water or a nitrogen environment for zero point calibration.
II. Air Calibration (Full-Scale Calibration)
Air calibration is the most commonly used calibration method for the Memosens COS81D, using the known oxygen partial pressure in air for full-scale calibration.
Operating Steps
- Remove the sensor from the process medium, rinse with deionized water, and gently wipe dry.
- Place the sensor in saturated humid air, avoiding direct sunlight and airflow disturbance.
- In the Liquiline CM44x menu, go to Calibration → Oxygen → Air.
- Wait for the measured value to stabilize, usually 3–5 minutes.
- After confirming the calibration value, press the confirm key, and the transmitter automatically calculates and saves the calibration coefficients.
After calibration is complete, the transmitter will display the new slope and zero point values. It is recommended to record and archive them.
III. Zero Point Calibration
Zero point calibration is used to eliminate the sensor residual current, usually performed when replacing the fluorescence cap or measuring low oxygen concentrations.
- Preparation of oxygen-free water: Bubble nitrogen into deionized water or add sodium sulfite.
- Calibration conditions: Immerse the sensor in oxygen-free water and wait for the reading to stabilize.
- Menu path: Calibration → Oxygen → Zero.
- Precautions: Zero point calibration should not be performed frequently, generally once every 6 months.
IV. Calibration Parameters and Comparison
The following table lists the key differences between air calibration and zero point calibration for users to choose as needed.
| Item | Air Calibration | Zero Point Calibration |
|---|---|---|
| Calibration medium | Saturated humid air | Oxygen-free water/nitrogen |
| Calibration frequency | Every 1–3 months | Every 6 months |
| Main function | Correct full-scale slope | Correct zero point residual current |
| Applicable scenario | Routine measurement | Low-concentration oxygen measurement |
V. Common Issues and Troubleshooting
If abnormalities occur during calibration, refer to the following troubleshooting points.
- Calibration failure: Check whether the fluorescence cap is aged and replace if necessary.
- Reading drift: Confirm that the sensor and transmitter are securely connected and the cable is not damaged.
- Slope out of range: May be caused by membrane contamination; clean or replace the fluorescence cap.
- Temperature effects: Ensure the calibration environment temperature is stable, and enable temperature compensation if necessary.
VI. Maintenance and Recommendations
Regular maintenance can significantly improve calibration success rate and measurement stability.
- Clean the fluorescence cap surface every 1–2 weeks to avoid biological attachment.
- Replace the fluorescence cap every 12 months, or shorten the cycle according to operating conditions.
- Calibration records should be saved in the transmitter or in paper archives for traceability.
- Use original calibration accessories to ensure compatibility with the Memosens COS81D.
Through standardized calibration and maintenance, the combination of Memosens COS81D and Liquiline CM44x can provide reliable dissolved oxygen measurement data over the long term.