There are some manufacturers who will recommend calibrating the oxygen sensors in water-saturated air. Others will suggest calibrating the sensors in air-saturated water. Then, there is the issue of inconsistency in calibration coefficient requirements.

The calibration of an oxygen monitoring sensor demands that the sensor is consistently subjected to a calibration standard that has a known value that the sensor is being adjusted and compared to. With a dissolved oxygen sensor, the calibration standard is usually an environment that is fully saturated with water and air, requiring some smart practices to be used along the way.

Knowing the Conditions Best Equipped for Calibrating Dissolved Oxygen Sensors

There are known conditions in an environment that’s fully saturated with air and water due to an accepted relationship between variable elements, including salinity, temperature, oxygen concentration, and barometric pressure. Knowing these values is paramount to establishing a strong calibration standard.

A lot of commercial dissolved oxygen sensors have a one-point calibration when at fully saturated conditions. The single calibration point allows the user to create a new low-cost calibration standard. Creating a fully saturated environment with air and water is the most basic requirement and can be done without using additional materials or equipment.

You can create the environment using 100% air-saturated water by filling a container with deionized water or clean tap water. The water temperature must reach equilibrium with the calibration environment. After shaking the container for around 30 seconds, you create 100% air-saturated water. Alternatively, you can wrap a wet towel around the oxygen monitoring sensor guard.

Meanwhile, you can calibrate dissolved oxygen sensors using a percentage saturation method, filling the calibration cup, so the temperature sensor and dissolved oxygen sensor are fully submerged in air-saturated water. When the water is stable and at equilibrium, a condition is created where the dissolved oxygen membrane and sensor match the temperature of the set calibration standard.

Creating a Checklist for Calibrating Dissolved Oxygen Sensors

So, when calibrating dissolved oxygen sensors, make sure that you:

1. Have air-saturated water with low ionic strength at your disposal
2. Use tap or deionized water
3. Ensure the calibration standard is under or oversaturated with oxygen
4. Make sure that the standard and atmosphere are equally calibrated temperature-wise
5. Have the right barometric pressure available at the time/place where the calibration occurred
6. Ensure the conductivity and temperature sensors are functioning properly while meeting accuracy specifications.

Learn more about dissolved oxygen sensors, how a dissolved oxygen probe works, and even more on our website.